Gustavo Ochoa-Vazquez

Boris Kharisov

Ana Arizmendi-Morquecho

Anaïs Cario

Cyril Aymonier

Samuel Marre
email: samuel.marre@icmcb.cnrs.fr

Israel López
email: israel.lopezhr@uanl.edu.mx

Microfluidics and surface-enhanced Raman spectroscopy : a perfect match for new analytical tools

Keywords: Terms -Microfluidics, Surface-Enhanced Raman Spectroscopy, Lab on a Chip, in situ characterization

I. INTRODUCTION

In the last decades, Raman spectroscopy has gained increasing attention as an analytical tool, being conventionally used to provide researchers with precious data for solving problematics in various topics such as environment, safety, biology and healthcare. This technique collects the inelastic dispersion with respect to an incident wavelength, allowing monitoring the vibrational modes of the molecules or material investigated. Due to the coupling to microscope, Raman spectroscopy can be used to perform (bio)chemical imaging at higher spatial resolution (less than 200 nm) that what can be typically obtained with Infrared spectroscopy [START_REF] Perro | Combining microfluidics and FT-IR spectroscopy: Towards spatially resolved information on chemical processes[END_REF]. However, this characterization tool is known to have a low sensitivity due to weak Raman scattering, which is one of the major problems associated with this technique. Therefore, for some specific applications, this has pushed researchers to consider one technique now widely used in Raman spectroscopy: The Surface-Enhanced Raman Scattering (SERS). This is a surface approach that enhances Raman scattering (the gain can reach a factor up to 10 10 , thus allowing the detection of trace molecules) due to the interactions between the investigated molecules and different nanostructured substrates constituted of noble metals generating localized surface plasmons and hot spots in between metals nanoparticles [START_REF] Otto | Surface enhanced Raman scattering[END_REF]. The fabrication of carefully-designed SERS substrates has been widely investigated; however, various challenges still exist in SERS, limiting its adoption by a wider scientific community, namely: the substrates fabrication reproducibility [START_REF] Geng | Gold nanochestnut arrays as ultra-sensitive SERS substrate for detecting trace pesticide residue[END_REF], the difficulty of realizing field measures and the high cost of analysis represent the most current problems [START_REF] Chen | Portable and Reliable Surface-Enhanced Raman Scattering Silicon Chip for Signal-On Detection of Trace Trinitrotoluene Explosive in Real Systems[END_REF]. With the purpose of addressing these limitations, the scientific community has look towards microscale processes through the use of microfluidics fundamentals.

Microfluidics is the scientific field that studies the behavior of the fluids and their control at microscale using microchannels displaying dimensions in the order of tens to hundreds of µm [START_REF] Fernandes | Connecting worlds -a view on microfluidics for a wider application[END_REF]. The design, fabrication and use of microfluidic devices have permitted to solve some problems related to the SERS technique, thanks to high precision and reproducibility in the synthetic and/or analytical parameters [START_REF] Ren | Facile fabrication of microfluidic surface-enhanced Raman scattering devices via lift-up lithography[END_REF], leading to the so-called MF-SERS approaches.

Over the past 10 years, an increasing number of studies have reported and reviewed the use of MF-SERS to miniaturize the analytical systems and to enhance their reproducibility [START_REF] Zhou | Sensors and Actuators B : Chemical Review of microfluidic approaches for surface-enhanced Raman scattering[END_REF]- [START_REF] Shen | A novel SERS-based lateral flow assay for differential diagnosis of wild-type pseudorabies virus and gE-deleted vaccine[END_REF] (Figure 1). The applications of such systems are wide, from chemistry to biology, including several medical (point-of-care -POC analysis) and analytical applications (trace molecules and drugs detection, etc.). All these researches have grown up over time, developing methods for general and specific applications based on MF-SERS devices.

In this perspective paper, we first introduce the general strategies for designing and fabricating MF-SERS devices and further introduce some of the current reported applications of MF-SERS. Eventually, a general perspective of this new analytical tool possibilities to other scientific fields will be presented.

II. COUPLING SERS WITH MICROFLUIDICS

One of the most important parts to consider when designing a MF-SERS experiment is the correct selection and fabrication/use of SERS substrates. These substrates are generally fabricated from the assemblies of nanoparticles or nanostructures of noble metals allowing generating the desired Plasmon effects, leading to the enhancement of the Raman scattering (nanoM with M = gold or silver). Several types of arrangements have been reported so far including metal NPs selfassemblies or core-shell (nanoM@ Al2O3 or nanoM@SiO2) [START_REF] Guo | Metal nanomaterial-based self-assembly: Development, electrochemical sensing and SERS applications[END_REF], [START_REF] Li | Shell-isolated nanoparticle-enhanced Raman spectroscopy[END_REF] pickering emulsions [START_REF] Ouyang | A new plasmonic Pickering emulsion based SERS sensor for in situ reaction monitoring and kinetic study[END_REF] or metals NPs-decorated oxides solids substrates [START_REF] Oh | Glass nanopillar arrays with nanogaprich silver nanoislands for highly intense surface enhanced raman scattering[END_REF]. Nevertheless, the complex fabrication procedures mostly exhibit low reproducibility, leading to a dispersion in the results.

When considering the integration of SERS substrates into microfluidics devices, additional difficulties arise, as several other considerations need to be taken into account. First, complicated microfabrication techniques generally have to be considered to integrate the substrates into a microfluidic chip. At the nanometer scale -required for such applications -it is not easy to control either the arrangement of NPs for a bottom-up SERS substrate approach [START_REF] Wu | Facile fabrication of microfluidic surface-enhanced raman scattering devices via lift-up lithography[END_REF] or the top-down manufacturing of substrates [START_REF] Deng | Rapid Fabrication and Characterization of SERS Substrates[END_REF]. Second, the physicochemical stability of the substrates exposed to additional stresses (fluid flow, chemicals, temperature, etc.) has to be carefully investigated, as it can result in a modification or even a failure of the substrate during experimentation, leading to poor reproducibility.

Nevertheless, there are several strategies that can be employed to generate SERS effect within microfluidic systems depending on whether the SERS substrate is in solution (colloids, nanoparticles aggregates) or fixed on a surface (solid substrates fabricated from top down microfabrication or bottom up in situ synthesis), see Figure 2, which corresponds respectively to: (i) SERS substrates dispersed in flow, (ii) integrated SERS substrates (top-down approaches) and (iii) immobilized SERS substrates (bottom-up approaches), which are discussed hereafter. Fig. 2. Strategies for the integration of SERS substrates within microfluidic reactors. (a) examples of SERS colloids: Gold nanostructures (nanotriangles, nanospheres and nanostars) used in flow (adapted from [START_REF] Tian | Surface enhanced Raman scattering with gold nanoparticles: Effect of particle shape[END_REF] with permission from The Royal Society of Chemistry), (b) microfabricated substrates based on plasmonic nanopillar geometry inside microchannel (adapted from [START_REF] Zhao | Plasmonic nanopillar array embedded microfluidic chips: An in situ SERS monitoring platform[END_REF] with permission from The Royal Society of Chemistry), (c) Silver NPs deposited inside of a microchannel as a fixed MF-SERS substrate (adapted from [START_REF] Chen | A highly sensitive microfluidics system for multiplexed surface-enhanced Raman scattering (SERS) detection based on Ag nanodot arrays[END_REF] with permission from The Royal Society of Chemistry).

Dispersed SERS substrates. The first strategy consists in using nanoM assemblies dispersed within the solution to analyze. This simple procedure requires the pre-synthesis of the nanoM assemblies (which size generally ranges from 20 to 200 nm) and their dispersion in the media. Several types of morphologies for the nanoM arrangements have been reported such as metal nanoflowers or nanostars [START_REF] Mulvihill | Anisotropic etching of silver nanoparticles for plasmonic structures capable of single-particle SERS[END_REF]. Indeed, the SERS effect is affected not only by the particle size, but also by their shape, and the distances between the metallic nanoparticles, generating controllable hot spots, driven by the localized electric field (Figure 2-a). The main interest concerns the easy manipulation and preparation of the samples, while the substrates can be recovered between analyses and cleaned to minimize cross contaminations. Nevertheless, solid handling inside microfluidics channels still remains challenging and some deposition of the nanostructured SERS substrates on the microchannel walls can occur over time, leading potentially to clogging of the device. Additionally, random aggregation of such nanoM colloids inside the solution may induce uncontrollable variation in the Raman signals. It is therefore highly desirable to pay attention to the fluidic design of the chips. The design and fabrication of microfluidic devices are not limited to their fabrication with only one microchannel to transport the fluid. Indeed, there are many possibilities to design microfluidic devices with different number of microchannels that expand their applications. For instance, Cui Y. et al show the use of a microfluidic system with different microchannels for the in situ synthesis and generation of gold SERS substrates and their performance evaluation [START_REF] Zhang | Combining Multiplex SERS Nanovectors and Multivariate Analysis for In Situ Profiling of Circulating Tumor Cell Phenotype Using a Microfluidic Chip[END_REF], [START_REF] Wang | Microfluidic chip based micro RNA detection through the combination of fluorescence and surface enhanced Raman scattering techniques[END_REF].

The advantage of this strategy is its easy operation and the use of nanoM previously synthesized as well as commercial nanoM. Also, in this strategy, is possible to recover and to clean the nanoM for reuse. This way, the chip can be used several times. However, undesirable clogging into the microchannels and nanoM agglomerations are hard to avoid, causing variation in Raman signals.

Integrated microfabricated SERS substrates on chip.

The second strategy concerns the generation of SERS substrate directly inside the channels, which is now been made possible thanks to the recent development of microfabrication techniques at nanoscale (Figure 2-b). Such approaches allow to design 3D SERS substrates for example through the fabrication of nanopillar arrays from silicon or glass [START_REF] Mao | Microfluidic surface-enhanced raman scattering sensors based on nanopillar forests realized by an oxygen-plasma-stripping-of-photoresist technique[END_REF], on the top of which thin metals layers can be sputtered or nanoM assemblies can be deposited for generating the desired SERS effect. Similarly, oxide nanoporous layers, nanotubes or nanowires (Al2O3, ZnO or TiO2) can be first grown on a planar surface and later decorated with nanoM assemblies [START_REF] Pisarek | TiO 2 and Al2O3 nanoporous oxide layers decorated with silver nanoparticles-active substrates for SERS measurements[END_REF]- [START_REF] Xie | SERS performance of graphene oxide decorated silver nanoparticle/titania nanotube array[END_REF]. These substrates are slightly more complicated to realize but lead so far to the best stability and reproducibility of the results thanks to a more homogeneous adsorption of molecules on the SERS substrates.

Among the various available fabrication techniques, it is worth mentioning the laser irradiation techniques [START_REF] Liu | Rapid Synthesis of Monodisperse Au Nanospheres through a Laser Irradiation-Induced Shape Conversion, Self-Assembly and Their Electromagnetic Coupling SERS Enhancement[END_REF], which allows accessing complex multi-materials nanostructures directly on chip. The principle consists in irradiating a metallic film with a laser, which will heat a precursor solution in contact with the film, leading to their decomposition and the heterogeneous growth of nanostructures. This approach was use in particular to grow 3D Ag@ZnO nanostructures for MF-SERS applications [START_REF] Xie | In situ fabrication of 3D Ag@ZnO nanostructures for microfluidic surface-enhanced Raman scattering systems[END_REF]. The laser direct writing approaches [START_REF] Zhang | Dual-3D Femtosecond Laser Nanofabrication Enables Dynamic Actuation[END_REF], is yet another interesting methodology, which allows accessing nanoscale structuration of MF-SERS substrates thanks to the recent development of femtosecond laser writing for the precise design of nanoscale structures.

Eventually, nanoprinting methodologies [START_REF] Chou | Imprint lithography with 25-nanometer resolution[END_REF], aiming at transferring through a mold sub-micrometer designs to a process able active layer, have quickly evolved over the last decades and can now easily be implemented to design metal SERS substrates at the nanoscale [START_REF] Liu | One-step fabrication of crystalline metal nanostructures by direct nanoimprinting below melting temperatures[END_REF].

Despite this strategy is expensive for the distinct microfabrication techniques at nanoscale and their hard training for operations, it presents great advantages. With integrated microfabricated SERS substrates on chip, it is indeed possible to design highly ordered and controlled nanoM SERS substrates for increasing the number of hotspots and the homogeneous adsorption of molecules, and thus to realize reproducible SERS analysis.

Immobilized SERS substrates within microchannels. This last strategy refers to the ordered spatial deposition of single metals nanoparticles or nanostructured materials inside of a microchannel (Figure 2-c). These immobilized SERS substrates constituted of nanoM arrays allow a fine control of the interparticle distance for improving the electrical field and the subsequent SERS effect. Thanks to advances in surface chemistry on glass or polymers, coupled to either nanoimprint lithography [START_REF] Suresh | Fabrication of Large-Area Flexible SERS Substrates by Nanoimprint Lithography[END_REF], electron beam lithography [START_REF] Abu Hatab | Surface-Enhanced Raman Spectroscopy Substrates Created via Electron Beam Lithography and Nanotransfer Printing[END_REF], focused ion beam [START_REF] Sivashanmugan | Nanovoids embedded in FIB-fabricated Au/Ag nanorod arrays for ultrasensitive[END_REF], or nanosphere lithography [START_REF] Willets | Localized Surface Plasmon Resonance Spectroscopy and Sensing[END_REF] approaches, these types of substrates can be easily modified for generating either homogeneous or heterogeneous patterns. Compared to the first strategy of flowing SERS substrates, these immobilized substrates reduce the Raman signal fluctuations and no specific microfluidic design are needed to handle solids assemblies. However, the main limitation remains: (i) the non-homogeneous molecules adsorption on the surface of the SERS substrate, (ii) the relatively high cost of fabrication, especially for the patterning part and (iii) the possible contamination of the MF-SERS devices over time as the cleaning of such substrates is not straightforward and might lead to particles desorption from the surface. Despite these limitations, such strategy is probably the most promising one to increase reliability of the MF-SERS devices as it provides ways towards the synthesis and the assembly of colloids directly on chip in a control manner. Since nanomaterials synthesis in microfluidics devices have been largely reported [START_REF] Marre | Synthesis of micro and nanostructures in microfluidic systems[END_REF], their further in situ assemblies (self-or orientated) could constitute a real advantage compared to the other reported strategies as the SERS substrate could be synthesized and shaped directly in a single step within microchannels. For example, Sepaniak et al. have worked with the microfluidic synthesis of nanostructures since 2004, creating different microfluidic SERS systems and testing their applications in various domains [START_REF] Riddle | Metal-polymer nanocomposites for integrated microfluidic separations and surface enhanced Raman spectroscopic detection Short Communication[END_REF]- [START_REF] Taylor | Surface enhanced Raman spectroscopy for microfluidic pillar arrayed separation chips[END_REF]. Summarizing their work, it was observed that for the correct synthesis and coupling of these materials, is necessary to provide an accurate design and fabrication of the microfluidic devices. Similarly, Xu and Giorgis have reported different techniques and materials of fabrication for the microfluidic devices, (PDMS, PDMS/silicon, PDMS/glass, glass-glass, paper using 3D printing, molding and soft lithography) [START_REF] Descrovi | Metal-elastomer nanostructures for tunable SERS and easy microfluidic integration[END_REF], [START_REF] Novara | Surface-enhanced Raman spectroscopy on porous silicon membranes decorated with Ag nanoparticles integrated in elastomeric microfluidic chips[END_REF]. They have demonstrated for all these materials the integration of synthesized nanostructures as SERS substrates for the generation of MF-SERS systems capable of performing in situ analysis [START_REF] Zhang | Combining Multiplex SERS Nanovectors and Multivariate Analysis for In Situ Profiling of Circulating Tumor Cell Phenotype Using a Microfluidic Chip[END_REF].

In spite of their disadvantages as high cost of fabrication, facile contamination and hard cleaning procedures, the principal advantage of this approach is the possibility for synthesizing and assembling the nanoM in situ into the microchannel and, with some microfabrication techniques create nanoM arrays with a specific interparticle distance.

We summarize hereafter (Table 1) the major advantages / limitations of each strategy. As described in the previous sessions, the main difference between these strategies lies in the investment / production costs and the enhancement factors (EF) and limits of detection (LOD) achieved. We will detail in the next section some applications of MF-SERS devices for several domains of research.

III. MF-SERS: A FULL RANGE OF APPLICATIONS

The first mention about flow-injection analysis coupled to SERS (FIA) at small scale was reported in the late 1980s by Laserna, Berthod, and Winefordner. They were able to detect 4-aminobenzoic acid using SERS in submillimetric channels [START_REF] Laserna | Evaluation and Optimization of Experimental Conditions for Surface-Enhanced Raman Detection of Analytes in Flow Injection Analysis[END_REF]- [START_REF] Winefordner | Surface Enhanced Raman Spectrometry on Silver Hydrosols Studied by Flow Injection Analysis[END_REF]. In the next decade, Caballin, Ruperez, and Laserna developed a windowless flow cell for the SERS detection of amiloride, amiphenazole, 2mercaptopyridine, pemoline and triamterene [START_REF] Cabalin | Flow-injection analysis and liquid chromatography : surface-enhanced Raman spectrometry detection by using a windowless flow cell[END_REF], [START_REF] Cabalin | Surface-Enhanced Raman Spectrometry for Detection in Liquid Chromatography Using[END_REF]. Since then, several other applications have been reported, among which are the research domains of environment, food monitoring for analytes detection and cells management and analysis on a chip, which are discussed below.

Analytes detection. The combination between microfluidic devices and SERS technique has allowed the better handling of analytes and the improvement of their assays. Thanks to the high sensitivity of SERS, miniaturized devices have been developed for portable detection of various molecules including pollutants [START_REF] Yea | Ultra-sensitive trace analysis of cyanide water pollutant in a PDMS microfluidic channel using surface-enhanced Raman spectroscopy[END_REF], drugs or narcotics [START_REF] Guo | Metal nanomaterial-based self-assembly: Development, electrochemical sensing and SERS applications[END_REF], as well as biomolecules such as DNA or pathogens [START_REF] Cangelosi | Duplex Microfluidic SERS Detection of Pathogen Antigens with Nanoyeast Single-Chain Variable Fragments[END_REF]. In particular, the most studied analytes are dyes including rhodamine 6G, crystal violet, and other Raman tags such as 4-MBA, due to their signal intensity, photostability, and their functional groups that permit specific bonding between these molecules and the SERS substrates [START_REF] Jacobs | Ultrasensitive Surface-Enhanced Raman Scattering Flow Detector Using Hydrodynamic Focusing[END_REF]- [START_REF] Wilson | Signal Enhancement of Surface Enhanced Raman Scattering and Surface Enhanced Resonance Raman Scattering Using in Situ Colloidal Synthesis in Microfluidics[END_REF]. Furthermore, this combination also has permitted the analysis of diverse inorganic samples highlighting the detection of metallic ions for applications in food safety and environmental monitoring [START_REF] Tang | Review-Surface-Enhanced Raman Scattering Sensors for Food Safety and Environmental Monitoring[END_REF], such as Hg(II) [START_REF] Chung | Trace analysis of mercury(ii) ions using aptamermodified Au/Ag core-shell nanoparticles and SERS spectroscopy in a microdroplet channel[END_REF], As(III) [START_REF] Qi | Surface-enhanced Raman scattering on a zigzag microfluidic chip: Towards high-sensitivity detection of As(III) ions[END_REF], Cr(III) [START_REF] Liang | Silver nanoparticle enhanced Raman scattering-based lateral flow immunoassays for ultrasensitive detection of the heavy metal chromium[END_REF] or Fe(II) [START_REF] Gouveia | A new spectroelectrochemical cell for flow injection analysis and its application to the determination of Fe (II) down to the femtomol level by surface-enhanced resonance Raman scattering ( SERRS )[END_REF]. The efficiency of MF-SERS platforms to be very sensitive, rapid, low-cost, non-invasive, highly selective and specific, has found various applications in clinical studies and drugs detection such as morphine and cocaine traces [START_REF] Kline | Optimization of Surface Enhanced Raman Spectroscopy Conditions for Implementation into a Microfluidic Device for Drug Detection Optimization of Surface Enhanced Raman Spectroscopy Conditions for Implementation Department of Biomolecular Science and Engine[END_REF]. Additionally, other interesting applications include the detection of explosives molecules as traces, mostly for security checking and military on site applications. Indeed, MF-SERS allow the fabrication of small, portable devices, which can be utilized in real environments. Besides, the MF-SERS analysis of explosive samples provide safer operating conditions with a small amount of sample, as reported for 4-ABT [START_REF] Zhao | Plasmonic nanopillar array embedded microfluidic chips: an in situ SERS monitoring platform[END_REF], DTN [START_REF] Piorek | Free-surface microfluidic control of surfaceenhanced Raman spectroscopy for the optimized detection of airborne molecules[END_REF], TNT [START_REF] Piorek | Free-Surface Microfluidics/Surface-Enhanced Raman Spectroscopy for Real-Time Trace Vapor Detection of Explosives[END_REF]. Other research areas that have been favored for MF-SERS use are biology and medicine for the detection of biomolecules, biomarkers and pathogens. Adenine, DNA, RNA, and different proteins are some biologic probes that are analyzed using MF-SERS combination due to facilitate the handling of samples using microfluidics parameters [START_REF] Chen | A highly sensitive microfluidics system for multiplexed surface-enhanced Raman scattering (SERS) detection based on Ag nanodot arrays[END_REF]- [START_REF] Calzavara | Single File Flow of Biomimetic Beads for Continuous SERS Recording in a Microfluidic Device[END_REF]. Similarly, diverse pathogens can also be detected with this approach, as reported for such as Escherichia coli, Staphylococcus aureus, and different mycotoxins in real samples using MF-SERS [START_REF] Lu | Detecting and Tracking Nosocomial Methicillin-Resistant Staphylococcus aureus Using a Microfluidic SERS Biosensor[END_REF], [START_REF] Walter | Featuring research from the group of As featured in : Lab on a Chip Towards a fast , high specific and reliable discrimination of bacteria on strain level by means of SERS in a microfluidic device[END_REF]. Eventually, the detection of different viruses as human immunodeficiency virus, HIV, type 1 [START_REF] Fu | A SERSbased lateral flow assay biosensor for highly sensitive detection of HIV-1 DNA[END_REF] and avian influenza virus, AIV, H7N9 [START_REF] Xiao | Ultrasensitive detection of avian influenza A (H7N9) virus using surface-enhanced Raman scatteringbased lateral flow immunoassay strips[END_REF] has been possible with the development of microfluidic devices and their link-up with SERS due to their ability to discriminate selectively the infected cells. All these proves of concept of SERS in medical applications and the miniaturization of the instrumentation permitted by the microfluidic devices have led to the fabrication of point-of-care (POC) devices. The POC systems present advantages as low-cost, field analysis as well as time saving in the training of personnel [START_REF] Quesada-Gonza | Nanomaterial-based devices for point-of-care diagnostic applications[END_REF]. Nowadays, it is possible to realize different analysis in patients without high personal training and in a faster way. There are several reports about POC tests using blood, saliva and urine as samples for the opportune detection of disease [START_REF] März | Detection of thiopurine methyltransferase activity in lysed red blood cells by means of lab-on-a-chip surface enhanced Raman spectroscopy (LOC-SERS)[END_REF], [START_REF] Hidi | LOC-SERS: towards point-of-care diagnostic of Methotrexate[END_REF]. This is currently the main trend for the development of MF-SERS devices.

MF-SERS for cell analysis.

The combination of microfluidic systems and SERS allows a high sample control of fluids flow and the generation of reproducible substrates for in situ analysis. Cooper et al., confirmed that the use of microfluidic systems allows a better sample control for cell characterization. Cells or bacteria can be manipulated one by one using microfluidic chips, due to the dimension of the Fig. 3. Examples of MF-SERS applications in the biological field. (a) droplets-based single cell microfluidics strategy coupled to SERS to investigated glycan expression in cancer cells at cellular resolution (adapted from [START_REF] Willner | Surface-Enhanced Raman Scattering Based Microfluidics for Single-Cell Analysis[END_REF] with permission from American Chemical Society), (b) scheme of a MF-SERS set-up and comparison results of both live and dead cell and isolated and grouped yeasts cells (adapted from [START_REF] Collins | In situ SERS probing of nano-silver coated individual yeast cells[END_REF] with permission from Elsevier B.V.). (c) MF-SERS set-up and results for the identification of six different mycobacteria from blood samples (adapted with permission from [START_REF] Popp | LOC-SERS: A Promising Closed System for the Identification of Mycobacteria[END_REF] with permission from American Chemical Society). microchannels and the low volume to control, allowing to analyze cells in an individually way. MF-SERS systems have been used for diverse biological analysis [START_REF] Monaghan | Bead-Based DNA Diagnostic Assay for Chlamydia Resonance Raman Scattering Detection within a Lab-on-a-Chip Format[END_REF]- [START_REF] Syme | SERS mapping of nanoparticle labels in single cells using a microfluidic chip w[END_REF] including single-cell analysis for improving the understanding of cellular systems. Indeed, cells can be encapsulated within droplets, which can be later stored in a microfluidic device and analyzed by SERS at cellular resolution [START_REF] Willner | Surface-Enhanced Raman Scattering Based Microfluidics for Single-Cell Analysis[END_REF] (Figure 3-a). Originally limited to medical / clinical studies, the use of MF-SERS could be extended to environmental biology for the on-field investigation of microbes [START_REF] Chisanga | Surface-Enhanced Raman Scattering (SERS) in Microbiology: Illumination and Enhancement of the Microbial World[END_REF]. In this research field, MF-SERS can be adapted to target the study of different microorganisms (fungi, viruses, yeasts and bacteria) based on their specific variations in spectral features. As an example, isolated and grouped yeasts cells were monitored in situ using MF-SERS coupled to integrated electrophoresis [START_REF] Collins | In situ SERS probing of nano-silver coated individual yeast cells[END_REF]. This approach was also used for the rapid identification of live and dead cells within aqueous environments, demonstrating the capability of MF-SERS to analyze biochemical molecules secreted during the cell growth, metabolism, proliferation and apoptosis (Figure 3-b). Another example concerns the used of MF-SERS for the differentiation of various mycobacteria in blood samples in short time demonstrating the high potential of these approaches for personalized medicine [START_REF] Popp | LOC-SERS: A Promising Closed System for the Identification of Mycobacteria[END_REF] (Figure 3-c). All these types of in situ analyses and monitoring approaches are of primary importance for several biological applications using microfluidics tool at lab scale.

MF-SERS in cells cytometry and liquid chromatography.

The SERS effect can be used as an efficient in situ detection tool coupled to flow processes at microscale. In particular, separation methods have largely benefited from microfluidic principles such as liquid chromatography, by introducing variants of the sheath-flow (hydrodynamic flow focusing) method [START_REF] Nguyen | Online Liquid Chromatography-Sheath-Flow Surface Enhanced Raman Detection of Phosphorylated Carbohydrates[END_REF], which are also widely used in cytometry. The sheath-flow is based on the splitting of a liquid sample within droplets or slugs thanks to the squeezing of the sample by another fluid (liquid or gas) within a microfluidic channel. In this context, Schultz et al. have been developing and using this method by controlling microfluidic parameters for sample separation and their analysis using SERS, generating different continuous processes [START_REF] Jacobs | Ultrasensitive Surface-Enhanced Raman Scattering Flow Detector Using Hydrodynamic Focusing[END_REF], [START_REF] Bailey | Sheath-Flow Microfluidic Approach for Combined Surface Enhanced Raman Scattering and Electrochemical Detection[END_REF]. Similarly, SERS technologies have designed for flow cytometry (SERS-activated cells sorting) [START_REF] Sebba | High throughput single nanoparticle spectroscopy[END_REF] and cell counting at microscale allowing detecting Raman signals in ultra-short time, as reviewed by Zhang et al [START_REF] Zhang | Towards high-throughput microfluidic Ramanactivated cell sorting[END_REF]. In situ SERS effect was also demonstrated for the detection and separation of molecules in liquid chromatography. For instance, Wang et al. have coupled HPLC with SERS for continuous separation and further detection of several analytes, providing an online characterization mean for the acquisition of molecular structural information of solutions [START_REF] Yuan | Rapid separation and on-line detection by coupling high performance liquid chromatography with surface-enhanced Raman spectroscopy[END_REF].

MF-SERS integrated platforms for micro-assays.

Some of the latest developments of MF-SERS concern the fabrication and use of all-in-one devices for fast screening at microscale. In particular, Popp et al. have worked on such microfluidics platforms for the synthesis, the separation, the mixing and the analysis of various types of samples. These platforms have been integrated with SERS for biological probe detection of cells in liquid media or biomolecules in urine samples [START_REF] Strelau | SERS as tool for the analysis of DNA-chips in a microfluidic platform[END_REF]- [START_REF] Patze | SERS as an analytical tool in environmental science : The detection of sulfamethoxazole in the nanomolar range by applying a micro fl uidic cartridge setup[END_REF]. Another application that uses the microfluidic concept is the lateral-flow assay (LFA). These assays are realized in paper strips in which capillary forces actions can carry an analyte in different stages onto the strip from their processing to the analysis stage [START_REF] Wang | Highly sensitive detection of high-risk bacterial pathogens using SERS-based lateral flow assay strips[END_REF]. Choo et al. employed this technique for realizing immunoassays [START_REF] Choi | Quantitative analysis of thyroid-stimulating hormone (TSH) using SERS-based lateral flow immunoassay[END_REF], virus [START_REF] Fu | A SERSbased lateral flow assay biosensor for highly sensitive detection of HIV-1 DNA[END_REF] and pollutant detection [START_REF] Lee | Quantitative Analysis of Methyl Parathion Pesticides in a Polydimethylsiloxane Microfluidic Channel Using Confocal Surface-Enhanced Raman Spectroscopy[END_REF], [START_REF] Quang | A portable surface-enhanced Raman scattering sensor integrated with a lab-on-a-chip for field analysis[END_REF]. The concept of microfluidic platforms for fast screening of the operating parameters has led to the realization of immunoassays using SERS as an analytical tool. These on chip devices have been used in particular for Immunotherapeutic molecules screening. [START_REF] Wu | In situ probing of cell-cell communications with surface-enhanced Raman scattering (SERS) nanoprobes and microfluidic networks for screening of immunotherapeutic[END_REF] Besides, the possibility to have different stages to realize different processes as LFA technique, plus all the possible applications that already exist in the state of the art, have incited researchers to study, design and fabricate devices as the Lab on a Chip (LOC) equipped with SERS probes [START_REF] Jahn | Surface-enhanced Raman spectroscopy and microfluidic platforms: challenges, solutions and potential applications[END_REF].

IV. CHALLENGES AND OPPORTUNITIES

The use of microfluidic fundaments for the manufacturing of systems capable to control, synthesize, separate and analyze very small volumes are promoting the growth of a wide panorama of possibilities and applications. Now that the coupling of microfluidics with SERS has been validated and used for several applications, the main challenges associated with MF-SERS could be the development of microsystems able to withstand harsher conditions to opens ways for analyzing more complex samples for applications in industrial processes (including high pressure, high temperature or aggressive chemical conditions). All the current publications on MF-SERS have mostly investigated aqueous media at room conditions, therefore leading to the use of polymers (PDMS mostly) as the microdevices fabrication materials. Being able to couple SERS with microreactors made of glass or silicon-Pyrex would provide more robust microsystems for enlarging the range of applications. This challenge would then also be associated to the need of developing stable SERS substrates integrated in such devices.

Besides enlarging the range of conditions, which could be used by MF-SERS devices, new nano-micro-fabrication processes are also highly desirable. In this view, the recent development of 3D nanoprinting approaches opens avenues towards the precise spatial design of MF-SERS devices down to few hundreds of nanometers [START_REF] Majumdar | Lithography-Free Self-Reconfigurable Post-Release Stress Engineering of Surface Micro-Machined MEMS Structures[END_REF]. This approach based on two photon polymerization technique and shadow masking for micropatterning was originally developed for tissues engineering [START_REF] Aleksandr | Three-dimensional microfabrication by two-photon polymerization technique[END_REF] before moving to micro electromechanical systems development (MEMS) [START_REF] Ward | Towards microscale flight: Fabrication, stability analysis, and initial flight experiments for 300 μm × 300 μm × 1[END_REF] and could possibly be easily adapted to designed MF-SERS devices.

Among the potential future applications of MF-SERS, POC devices are probably the most promising ones, given the growing demand for personal healthcare solutions. To reduce the fabrication cost of MF-SERS devices for such applications, paper-based SERS microfluidics substrates [START_REF] Torul | Paper membrane-based SERS platform for the determination of glucose in blood samples[END_REF]- [START_REF] Lee | Fabrication of a SERS-encoded microfluidic paper-based analytical chip for the point-of-assay of wastewater[END_REF] should be a great alternative to conventional microfabrication techniques. The low cost and easy fabrication principle consist in impregnating noble metal nanoparticles within a conventional paper microreactor. Besides their cheapness, these MF-SERS substrates also allow overcoming the signal fluctuations sometimes encountered in liquid-based MF-SERS.

Environmental biology is yet another example of future applications for MF-SERS thanks to the portability and miniaturization of the devices, which can be used directly on field. In this context, such tools could be used to investigate the biosphere. Indeed, the vast majority of microbes from natural environments is still mostly unknown, but largely contribute to the Earth global carbon cycle. MF-SERS platforms operating in harsh conditions could therefore offer a unique opportunity to better understand endemic microbes in their environments.

It is also worth mentioning the recent use of 3D living cells mapping with confocal Raman spectroscopy, which could also largely benefits form the combination of microfluidics systems with SERS effect. The major advantage of Raman in such studies relies on the ability to work with label-free sample, preventing from bias, which can be induced by the use of tag molecules, generally needed in fluorescent laser confocal microscopy [START_REF] Majzner | 3D confocal Raman imaging of endothelial cells and vascular wall: Perspectives in analytical spectroscopy of biomedical research[END_REF]. Nevertheless, the major limitations mostly reside in the low signal to noise ratio of some particular vibration bands characteristics from specific proteins or biomolecules. In that view, SERS could easily be used to overcome this limitation [START_REF] Huang | 3D SERS (surface enhanced Raman scattering) imaging of intracellular pathways[END_REF], [START_REF] Mcaughtrie | 3D optical imaging of multiple SERS nanotags in cells[END_REF] and combined to microfluidics, this should provide advanced working environments for the culture, detection and analysis of living cells (Figure 4-a) and the microbiology research field in general (Figure 4b). Fig. 4. Examples of living cells SERS mapping. (a) 3D volumes of intensity distributions of human induced pluripotent stem cells, and adult rat ventricular cardiomyocytes for selected bands: 1,008 cm -1 for cell cytoplasm (blue), 789 cm -1 for cell nucleus (red), 2,857 cm -1 for lipids (green), 485 cm -1 for glycogen (white) and a merge of all components; scale bar 10 µm. (adapted from [START_REF] Kallepitis | Quantitative volumetric Raman imaging of three dimensional cell cultures[END_REF] with permission from Springer Nature), (b) molecular composition of Leishmaniainfected macrophage cells in vitro by SERS (adapted from [START_REF] Živanović | Chemical Mapping of Leishmania Infection in Live Cells by SERS Microscopy[END_REF] with permission from American Chemical Society).

Eventually, Stable Isotope probing strategies could also be implemented in MF-SERS for identifying microbial cells at different levels of substrate incorporation in a complex microbial community, as recently exemplified using conventional SERS [START_REF] Wang | Single cell stable isotope probing in microbiology using Raman microspectroscopy[END_REF], [START_REF] Cui | Surface-Enhanced Raman Spectroscopy Combined with Stable Isotope Probing to Monitor Nitrogen Assimilation at Both Bulk and Single-Cell Level[END_REF]. Overall, from the current research general tendency, it is foreseen that MF-SERS will move within the next 10 years from conventional laboratory uses to the palm of our hands.

V. CONCLUSION

Microfluidic has allowed to improve the separation process and analysis of inorganic, biological and environmental samples. Furthermore, the nature of design and fabrication for microfluidic devices has permitted the coupling of the SERS analytical technique, generating new technologies capable of carrying out more than one process in one place as shown by the multiple applications and potential of the MF-SERS devices.

Recent strategies have been employed to generate reproducible SERS substrates depending on if the substrate is in solution or fixed on the surface. Dispersed SERS substrates in flow, integrated microfabricated SERS substrates on chip and immobilized SERS substrates within microchannels are the most recent strategies for SERS substrates microfabrication. However, some limitations as random aggregation of nanoM colloids, uncontrollable synthesis inside of a microchannel, non-homogeneous molecules adsorption and the relative high cost of fabrication are present in these strategies it is important try to solve them. Even so, with all these limitations, the coupling between microfluidics and SERS technique has permitted a wide range of applications.

Nowadays, MF-SERS had allowed different applications as analytes detections, cells analysis, cytometry and liquid chromatography. Different analytes have been detected as pollutants, drugs, explosives, biomolecules, DNA or pathogens because of the facility of portable microfluidic devices fabrication. Due to the wide use of these devices on medicine and biology, it has been extended the use of POC as a field analysis tool for the opportune detection of disease.

Besides, MF-SERS devices have allowed in situ analysis. Different microorganisms as fungi, viruses, yeasts and bacteria, can be handled one by one using these devices, analyzing them in an individually way.

The separation methods have benefited with the control of flow processes using microfluidic devices. The cytometry and the liquid chromatography are techniques that have been improved with the coupling of MF-SERS devices, developing SERS-activated cell sorting and cell counting. Also, HPLC with SERS provides an online characterization.

Another use of MF-SERS is in the design of platforms for microassays. Lateral-flow assays and all-in-one devices have been developed to realize different processes at the same time, becoming them to LOC devices.

Therefore, MF-SERS devices have permitted an improvement in the way to analyze and to control different samples, opening a wide range of possibilities that will allow to enlarge the knowledge on the fields of chemistry, biology and medicine.

Fig. 1 .

 1 Fig. 1. Advances of MF-SERS over time.

Table 1 :

 1 Comparison of the advantages and limitations of each abovementioned methodology.

		Dispersed	Integrated	Immobilized
	Feature	MF-SERS	MF-SERS	MF-SERS
		substrates	substrates	substrates
	Fabrication cost	$	$$$	$$
	Viability of reuse	easy	hard	medium
	Maximum EF reported	10 9	10 12	10 10
	Minimum LOD reported	10 -8 M	10 -6 M	10 -12 M
	Chip platform	PDMS-glass	PDMS-glass, PDMS-Si	PDMS-glass, all-PDMS
	Analysis time	60-80 min	5 min	5 min
	Manufacturing infrastructure	basic	sophisticated	intermediate
	Example applications	biomolecules, cancer diagnosis	biomolecules, cells	biomolecules, drugs, dyes

The authors acknowledge the Consejo Nacional de Ciencia y Tecnología of Mexico (CONACYT) for the Ph.D. research scholarship of G. Ochoa (610186). This work has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant Agreement No. 725100, project Big Mac). 1 I.


1

The "Confucianization" seen with the eyes of its initiators.

The words of Yulgok Yi I

SANCHO Isabelle (Dr., INALCO) In the panel entitled the "Confucianization of Korean society", I have chosen to take a restrictive approach to this complex and multi-faced problem. I first proposed to examine what we could call the "confucianization of the elite", or the confucianization of the scholarofficials. There were many reasons for this preliminary choice. First, a difference has to be made between the Confucianization of the whole society, which is a long-lasting process extending over the entire Chosŏn period, and what pr. Kim Haboush used to call the "Confucianization of the court", that is to say the Confucianization of the elite or of the scholar-officials. This Confucianization of the scholar-officials is in some extant the first stage of the Confucianization of Korean society, because this particular social class is considered as the main dynamic force that introduce, develop and maintain Confucian institutions, values and practices at court first, and then in local areas. A second difference has to be made between the Confucianization taken as an impersonal process which features could be factually, objectively described, and the Confucianization taken as a deliberate project led by the supposedly "confucianized" elite. But, many questions could then arise: was there really a conscious project of confucianization, and if it was so, what was the motivation of these men who try to "confucianize" Korea? Besides, generally speaking, the 16 th century can be seen as a turning-point in the process of Confucianization. While the Confucianization of the court is generally considered as achieved, the growing power of the Censorate -and especially the samsa -endangers royal effective power. Factional strives are emerging, and they create a sort of breakdown in the balance of power at court. In a very short period of time, these strives spread to local areas and they divide the whole world of literati. And, finally, the scholars start to lead by themselves the Confucianization of the country. They are creating sŏwŏn and hyangyak and they develop their educational and social activities independently of the State. To sum up and to have a very general picture, the 16 th century is the scene of a crisis in the history of Chosŏn political functioning, and also the scene of the beginning of an active Confucianization of the society not only led by the State but primarily by the scholars-officials who also tend to create a new identity for themselves.

That is why I have entitled my presentation the "Confucianization seen through the eyes of its initiators". And for this purpose, I have chosen a case study much more suitable for a short speech: the case of Yulgok Yi I, taken as an example. The main reasons for this choice are that Yulgok was undoubtedly a Confucian. He was a high official and he faced the beginning of the factional strives and experienced the problems caused by this phenomenon at the very heart of the court. He also participated in the creation or the redefinition of the rules of the sŏwŏn and the hyangyak. And he left many writings which give us the opportunity to confront and compare different kinds of sources.

The aim of my study is then to draw a general picture of the mental representations of that period through a study of the terminology used by Yulgok in his various writings: mainly his dissertations, his personal and official correspondence. Such a picture of the mental representations could be interesting in order to better know what it means to be a Confucian scholar-official at the end of the 16 th century, and to what problems the Confucianization is connected with when we try to think about this phenomenon from the "inside", or from the scholars' viewpoint.

For a start, we can notice that there are very few explicit mentions made to what we call nowadays "confucianization" in Yulgok's writing. The "confucianization", or in other words the Confucian mission of the scholars-officials to civilize their country could correspond to the well-known idea of p'ung (the wind), which comes in the following variety of compounds: munp'ung (related to yusŭp), yup'ung (related to the civilization, mun), sap'ung. These three terms are used equally by Yulgok, just as if they were synonymous.

However, in the case of sap'ung, we can notice that this term is linked in the texts with three main ideas. First, it is the idea of officialdom that mainly expresses the fundamental unity between the sap'ung and the activity of the central government at court. The second idea is the educative and civilizer mission of the elite. And, the last idea is the spread of Confucian education. Besides, when Yulgok is speaking about this "mission", this p'ung, he is stressing the deficiency of contemporary yusŭp, the habits and attitudes of the Confucians. For him, to improve the sap'ung needs to "cultivate the scholars, the sa" (yangsa). And, yangsa needs in turn to transform radically the yusŭp or sasŭp through a beforehand reformed educational process. This preliminary remark shows that for Yulgok, the Confucianization is led by the scholarly trained Confucian officials (yu or sa), and his major concern is the education of this specific social group that shares the power with the king. So, the Confucianization of the society starts with the confucianization of the scholar-officials, and these men are the main focus of interest for Confucians like Yulgok.

Deceived by this first research on the "Confucianization seen from the inside", I have made another research on the terms used by Yulgok which leads to much more interesting conclusions. Indeed, I have studied the terms designating what we call in Western languages the "scholars-officials", in order to know much about the self-awareness of this social group. Indeed, if the "mission of confucianization", considered as an educational project based on Confucian values, is commonly and explicitly shared by all the scholar-officials of the same aristocratic class, how does this elite actually picture herself?

When Yulgok is talking about the scholars-officials as a social class, in contrast to common people or the rest of the country, he uses the following terms: yu (identified with munban), sega chi ye (the men who have an "aristocratic" ascendancy, that is to say a high officials' lineage), nongmin (in the sense of gentleman farmer or land owner), sasŏ chi ka and hakcha. As regards the case of hakcha, Yulgok contrasts it with the sok'in (common people), and the ya'ina term referring to the idea of the decay of a scholar-official. Sok'in and ya'in imply moral and social connotations. So, the main terms designing the scholarsofficials (yu, ka, min, sa, hak), when compared to what Yulgok is explicitly saying, tend to show that this social class is anxious to be thought honourable and defines itself as a ka (or kamun) identified as a high-officials' lineage. The specificity, and also the legitimacy of this class lie in an expertise (the scholarly expertise, hak and yu) and the corresponding attitudes and habits (ritual practices for example). So, the group seems to be homogenous and unitary, compared to the "lower classes" which are not at all discussed in detail.

When Yulgok talks about the people, or the nation, in contrast to the king, he does not care either about lower classes called by a generic term: min. But he does make a difference between the sin (ministers/officials) and the sa, or between sa and cho (the "court", an equivalent of sin/officials). Moreover, he makes a difference between the sa and the cho on the one hand, and the chija (the "capable men", the true Confucians) on the other hand. He is contrasting the scholars-officials taken as a group, to the true Confucians who are regarded as outstanding individuals. So we can notice that, depending on the viewpoint, differences are made among the unitary social group of scholar-officials.

Let us continue the investigation by a deeper analysis of the terminology used for the scholar-officials in Yulgok's writings. We will examine successively the following four major groups of terms: 1) sa (designating a social group in relation to specific skills and practices), 2) sin (taken in the sin/kun relationship, or related to officialdom), 3) yu (related to Confucianism and scholarly expertise) and 4) several terms formed from the notion of hak/Learning, also related to Confucianism.

The terminology based on the term sa is certainly the most complex and difficult to define. These numerous terms designates a general and homogenous social group (sa, saja, wuisaja, sasŏ, saryu), but also a group that can be divided in different categories (hakmun chi sa, sarim, sallim or sallim chi sa, ch'usa). Besides, the moral value of the distinctive sa is often underlined by qualifying adjectives: chisa, chiksa, hyŏnsa, ŭisa just as if being a sa does not necessarily match moral qualities. But, on the contrary, sa is also used to designate specific features, or specific skills inherent to the sa's status or identity: sasŭp, sagi, sasim, sap'ung, sap'ip, saron.

The terminology based on the term sin (taken in contrast to the king, kun/wang) is at first sight easier to characterize. First, there are generic terms designating some specific officials at court: taesin (high officials of the samsa), myŏngsin (high officials of the Ming court), nansin (the bad officials who are responsible for the sahwa). But, the most important term is certainly sega chi sin and its abbreviation, sesin. These terms designate a sa who became an official because of, or thanks to his high officials' ascendancy. So, the expression is linked to the problem of the legitimacy of the high social status. The antonym of sega chi sin is sallim chi sa, or even pulsu sallim chi sa (the scholars who refuse to be sold as common goods, who refuse to prostitute their ethical and scholarly life to the administration). We can notice that the expression ch'oya chŏksin refers to the retired scholars who have been officials and have deliberately chosen to retire for moral and/or vital safety.

The terminology based on the term yu, usually translated "Confucian", reveals an interesting polysemic use. Yu designates a social class, that of the munban in contrast to the muban. It designates also the school of the Confucians (yuja, sŏnyu, kuyuja). But, some terms refer to specific contemporary Korean scholars: yusaeng (official students in state schools or in Sŏnggyungwan), and noyu sŏnsaeng (local scholars who teach basic knowledge for the kwagŏ examinations but are ignorant of the real Confucian learning). Just like in the case of the term sa, a yu is not necessarily synonymous with inborn moral skills and true abilities for officialdom. The examples of t'ongyu, uyu, puyu or paekmyŏn puyu reveals that qualifying adjectives are often used. But, just like sa, yu can on the contrary express specific and remarkable qualities: i yu myŏng se (to gain fame thanks to one's yu skills, or yu qualities) and yuhaeng (acting as a true yu). Lastly, yup'ung, related to yusŭp, refers to the Confucianization, or the educative mission of the Confucians, and their ability to improve civilization.

The last group of terms designating the scholar-officials is based on the term hak which refers clearly to Neo-Confucianism, and especially Cheng/Zhu Neo-Confucianism as interpreted during the Yuan dynasty. Indeed, hakcha, wuihakja, and tongbang hakja designate the followers of the sirhak, or sŏngnihak, or yihak or sŏnghyŏn chi hak. The latter term, sŏnghyŏn chi hak (the "Learning of the Sages and Worthies"), and the first one, sirhak ("practice-oriented Learning") are particularly meaningful, because they indicate the political horizon of the Neo-Confucianism adopted in Korea, which was intended primarily for the governing elites. Compared to other teachings, Confucianism or hak is opposed to yidan and yiryu and it is named odo or sado (two terms that stress the unity of the "Confucian hak" or the only one To). There are also some expressions that clearly link the hakja or the Confucians with the figure of Confucius: kongja chi to, pŏp kongja chi to. But, we can notice here too that acting superficially as a follower of Confucius does not necessarily mean being in the right way, as shown in the expressions pok kongja chi pok (wearing the clothes of Confucius) and song kongja chi ŏn (reciting the speeches of Confucius). These examples are of high interest because, when using these terms, Yulgok exposes the superficial ritual attitude and the superficial knowledge of Confucian classics of the supposed or "false" Confucians who are just using Confucian practices and references as a means to gain social recognition.

Before concluding, let us see now one last terminology used by Yulgok: the typology of the retired scholars of his time, the sa chi pulsa (literally the "scholars who do not want to serve"). Indeed, after the beginning of the factional strives at court, Yulgok exposes in two letters to the king his own terminology to designate this particular category. The yuhyŏn are the ideal Confucians who must serve for the sake of the government and the whole country.

The ŭndun chi sa are a sort of hermits who are not unconcerned about state affairs, and it is up to the king to persuade these capable men to serve in his government. The yŏmt'ui chi sa (the category where Yulgok classifies himself) are described as having some outstanding abilities.

But, because they are also aware of their shortcomings, the king must leave them retire for self-cultivation, and summon them when they will be ready to serve with efficiency. The last category, that of the tomyŏng (chi sa), refers to the unscrupulous scholars who wrongfully assume the title of sa.

Many conclusions could be drawn from this analysis of the terminology used by Yulgok in various types of texts, but I will just underline a few ones. Firstly, there is no particular term to designate the scholar-officials as a social class. Indeed, there is a vagueness in the use of the terms sa, yu, sin and hakja, even if there are also many evident signs that Yulgok has a clear "class awareness". Secondly, the terms yu, sa, kongja chi to, hakja do not refer necessarily to any moral qualities that would be inherent to the status they are designating. So, the supposed moral superiority and the scholarly expertise of the scholarofficials are the crucial problems for defining the identity and the self-awareness of this class, in search for recognition.

Generally speaking, what is striking is that, whatever the nature of the texts, Yulgok shows a great concern for the definition and the categorisation of the different types of scholar-officials. His typology of the contemporary "retired scholars" is especially interesting because it mainly reflects his attempt to make clear distinctions among the indistinct group of scholar-officials. So, the vagueness of the vocabulary, the contradictions in the terminology in his texts display on the one hand the lack of a clear representation of his class and of its specificities, duties and legitimacy, and on the other hand a great concern for a self-definition as a scholar, an official or an aristocrat. This leads us to consider the question of Confucianization. Indeed, we could maybe interpret this vagueness and this concern for a definition as signs of the feelings of insecurity and disarray.

The theoretical discourse and the philosophical exegesis of the scholar-officials, from the foundation of Chosŏn, have mainly stressed the necessity of a collegial power, a sharing of the power between the king and the "scholar-officials" taken as a group. These scholarofficials have been used to picture themselves as a unitary body, in contrast to the figure of the king. And, whatever the name we give to them (gongsin, sarim, hungup'a, etc), there is no doubt that they have all experienced sahwa and various hardships for many centuries. But, if they share a common history, they have been deeply divided since the very foundation of the new dynasty. Yulgok's example suggests that, at the 16 th century, they seem to put words on this division. Besides, we could also wonder if they are not beginning to proclaim the difference between the figure of the official (or bureaucrat) and that of the scholar, sŏnbi.

More precisely, they could have been in search of a new identity that could relieve them from the duty of serving -a duty which has legitimated their existence as an aristocratic social class.

So, the Confucianization of the whole society, led by the scholars in local areas from the end of the 16 th century on -a process that I would call a "mass confucianization", mirrors perhaps the progressive construction of new mental representations, of a new self-awareness for Chosŏn Confucians.


come

So this lack has led to study the history of Korean kyŏnghak 經學 mainly through a few great figures as well as a few well-known texts. Moreover, in spite of a few recent studies in the history of texts and printings, kukŏhak 국어학 or general socio-political history, the Confucian scholars have mainly been studied for their philosophical systems. They have been classified according to the general trends or schools -often rival schools or political factions -that they are supposed to embody. So kyŏnghak has mainly been regarded as a sub-genre of Neo-Confucian thought taken as a philosophy.

Research that would only focus on the very history of Korean commentaries, by themselves and not as erudite illustrations -or even symptoms -of larger philosophical systems, is still to be done.

The second problem is the well spread idea that the history of Chosŏn Neo-Confucianism can be analysed through the opposition "Zhujahak chŏk scholars" versus "t'al Zhujahak chŏk scholars", that is to say according to the different attitudes adopted by scholars toward the so-called Zhu Xist orthodoxy. Such a vision tends however to draw the following general picture of the history of Chosŏn Neo-Confucianism, which is not really satisfying: from the 14 th to the 16 th century, reception of Neo-Confucianism and faithful -even blind -reverence for Zhu Xi's orthodox school from the 17 th century, reactions to this orthodoxy (with a special interest given to the so-called sirhak scholars, whose autonomy of thought is highly praised) and finally, the 18 th and 19 th centuries as the golden age of Korean scholarship on the Classics, embodied by prominent figures like Tasan Chŏng Yagyong. This later period has therefore massively attracted contemporary scholars, and Korean kyŏnghak is then generally thought as synonymous with sirhak, kojŭnghak 考證學, 18 th century philological "rediscovery" of the Classics, and finally with the criticisms against orthodoxy, Zhu Xi, official learning and kwanhak 官學.

These two problems have led to neglect, or even simply forget some interesting connate problems in political and socio-cultural history when dealing with the use and After this first, close distance vis-à-vis the text, a second attitude can be noticed, which consists in commenting texts, in a both philological and philosophical thought process. This attitude is better illustrated at the 15th and 16th centuries by Confucian scholars, rather than kings. Indeed, even if most of the kings were taking good care of participating in the reading discussions on the Classics during the Royal Lectures The formalisation of correct Korean versions of basic texts in the form of ŏnhae is indeed pointing at the royal desire to promote, control and edit an official corpus. This corpus is meant to be spread in the whole country, but also to be given as royal gifts to a few scholars-officials. This shows the royal will to edict an official doxa but also -and maybe above all -to head any individual exegesis, which would only credit one single scholar. This is certainly one of the reason why king Sŏnjo did not use the already existing Yulgok's ŏnhae of the Four Books, and gathered instead a group of scholarsofficials to write a collective work to be used as official reference book.

Yet, scholars themselves were showing the same will of unification, of course for different reasons. As for example, T'oegye and Yulgok are explaining that they are writing the Samgyŏng sasŏ sŏkŭi and the Sŏnghak chipyo to put an end to the

AKSE Conference

-6 -exponential growth of Classics and commentaries, and thus to make a synthesis that could be a parapet against extrapolations. Extrapolations -they say -are evil, for they are misleading young scholars. They are useless and time-consuming, whereas scholars must only concentrate on Learning -that is to say the Confucian learning -which is so demanding that it needs a life-long commitment. There is no room for trifles and banalities when a higher mission is at stakes. Indeed, the goal of learning is to live according to it. In other words, Confucian Learning has always been stressing ethic and praxis, rather than solely textual knowledge.

This point is really worth reminding, for even the so-called orthodox, Zhu Xist Neo-Confucian tradition has been calling for sirhak 實學 (practice-oriented learning)

since its very beginnings. So beyond their enabling the social reproduction of the elites, the Classics and the Neo-Confucian textual knowledge have been seen as the means to put theory into pratice, or to "perform" texts and ideas (Confucianism might indeed be defined as the philosophy of the "just do it"). As Yulgok said in the Kyŏkmong yogyŏl:

  and scholars in the first half of Chosŏn. Isabelle Sancho (Collège de France) Confucius said « 溫故而知新,可以為師矣 », « Reviving the old to know the new may be taken as a model » (Lunyu, II.11). Confucianism might indeed be defined as an exegetical tradition, "reheating" (literally) and constantly reviving old texts and old ideas in order to find new flavours and new arrangements for the present. Studying today this exegetical tradition in Korea leads however to face two major problems: the lack of comprehensive compilations of Korean sources on the one hand; and some wellestablished historiographical presuppositions about the history of Korean Confucianism on the other hand. Firstly, contrary to Ming and Qing China that published several comprehensive compilations of Chinese commentaries on the Classics, both official and private (as for example: Sishu wujing daquan 四書五經大全; Xingli daquan 性理大全; Sishu quanshu 四庫全書, « 經部 »; Huangqing jingjie 皇清經解 ; Tongzhitang jingjie 通志堂經解), the rarity of Chosŏn Korea's compilation of specifically Korean commentaries is striking. The first one can be traced back to the 17 th century. It is the 海東文獻總錄, 經 書 類 (1637) of Kim Hyu 金 恷 (1597-1640), which compiles some Korean commentaries from the end of Koryŏ to Yulgok, Yi I 李 珥 (1536-1584). In the Yŏngnam school, the Tongyu sasŏ haejipp'yŏng 東儒四書解集評 of Yu Kŏnhyu 柳健 休 (1768-1834) could also be cited, in spite of his slight bias in favour of T'oegye's school. The first official compilation, which consists only in a bibliographical listing of titles, is the Tongguk munhŏn pigo 東國文獻備考 from the reign of Yŏngjo 英祖 (1694-1776), written on the model of the Wenxian tongkao 文獻通考 of the Song scholar Ma Duanlin 馬端臨. It has been successively revised and extended under Chŏngjo's reign and, after that, in 1903, and was finally renamed chŭngbo munhŏn pigo 增補文獻備考 in the final 1908's edition. To compensate this lack of a comprehensive compilation of Korean commentaries, the Tong'asia haksulwŏn of the University of Sŏnggyungwan has been compiling for ten years and finally published in 2009 AKSE Conference -2 -1998 the Hanguk kyŏnghak charyo 韓國經學資料, available online at the 한국경학자료시스템 since 2006. However, this "Collection of the Korean Study of Confucian Classics" is not comprehensive either, as Korean scholars pointed out recently. For example, most of the texts or passages commenting the Classics in personal correspondence, poems or biographies are not taken into account and not listed.

  Confucian canon in the course of Korean history. I would like to present here some very general reflections about the first Korean Neo-Confucianism, the orthodox one, going from the 14 th century to the late 16 th century. Yet, in order to narrow my presentation, I have chosen to focus on two possible aspects of the features, role and use of this orthodox corpus by both Chosŏn kings and scholars: 1) what I would tentatively call the distance taken vis-à-vis the texts, 2) the purposes of reading and commenting these texts.So let us first have a look at the distance -short or long -that kings and scholars have taken from the canonical texts and Neo-Confucian literature at large, when reading or using them. The scale is pretty wide, but three general standpoints can be distinguished.Firstly, there is a very close distance, a close attitude, which consists in fixing a unified version of texts. This attitude has mainly been illustrated by kings, who wanted to perform their duty of kyohwa 教化, that is to say the duty of being Sage rulers in a Confucian worldview. An official policy has been carried out by three different kings in the 15th and 16th centuries to achieve a unified version of the Four Books, the Three Classics but also a few other texts that were not, namely, canonical -like the Xiaoxue 小學 of Zhu Xi's school. This policy has started with several royal editions of ŏnhae 諺 解 and kukyŏl 口訣, the annotations in either Classical Chinese or Korean to help basic understanding as well as recitation in Korean pronounciation.Sejong 世宗 (1418Sejong 世宗 ( -1450) ) is the first king to have started this process. He is recorded in the Annals as having ordered the Korean translation of the Four Books. Besides it is noteworthy that Sejong also created the Chiphyŏnjŏn 集賢殿 and promoted the system of saga toksŏ 賜暇讀書 (a kind of paid sabbatical leave for studying) that allowed many scholars to study, comment and write texts under royal patronage. The second king, Sejo 世祖 (r. 1455-1468), not only ordered a systematic annotation and explanation in Korean of Confucian texts -as well as Buddhist canonical texts; this is worth reminding, since the practice of kukyŏl started in Korea with Buddhist texts -, but he also made himself the kukyŏl of the Xiaoxue 小學 and the Yijing 周易. The third and maybe the most important king is Sŏnjo 宣祖 (r. 1568-1608), who created the Kyojŏng ch'ŏng 教正廳 in 1585 for a new annotation of the Classics (kyŏngsŏ ŏnhae). The result of this long-lasting work, which 2009 AKSE Conference -4 -has been interrupted by the imjin Japanese invasion, was finally completed and published in 1628, producing the orthodox, official version of the Korean ŏnhae of the Four Books, the Three Classics (周易, 書經, 詩經), the Sohak 小學 and the Book of Filial Piety 孝經 : the kwanbon ŏnhae 官本諺解. Other examples of royal patronage over the canonical texts can also be later found in the printing of official editions reproducing royal family's handwritings (example of the Mengja ŏnhae 孟子諺解 printed in 1693 and based on the calligraphy of Injo's father, Wŏnjong), or in the addition of royal autograph or preface to outstanding works related to Classics (example of Chŏngjo's preface to Yulgok's Kyŏkmong yogyŏl 擊蒙要訣).

(

  kyŏngyŏn 經筵), they were not as involved as the elites in the deep study of texts, since the elites of the beginning of Chosŏn were socialy and morally bound to be literati, scholars, exegetes. They were legitimising their social status precisely by the mastery of Confucian texts. These commentaries of canonical and neo-confucian texts by successive scholars are revealing a huge diversity in the reading practices of that time, ranging from compiling canonical quotations and their Neo-Confucian commentaries, achieving an overall synthesis of various texts, writing erudite linear commentaries, or providing systematic and personnal understandings of the Neo-Confucian thought. Four outstanding examples of such erudite commentaries and/or compilations from the 14th to the 16th centuries are the ogyŏng ch'ŏngyŏllok 五經淺見錄 of Kwŏn Kŭn 權近 (1352-1409), the Chungyong kukyŏng yŏnŭi 中庸九經衍義 of Yi Ŏnjŏk 李彥 迪 (1491-1553), T'oegye Yi Hwang's Samgyŏng sŏkŭi 三經釋義, Sasŏ chil ŭi 四書質疑 and Sasŏ sŏkŭi 四書釋義, and finally Yulgok Yi I's Sŏnghak chipyo 聖學輯要. All these examples are telling two important things that are noteworthy here, even if they might sound like truisms. Firstly, commenting texts mainly means commenting commentaries, rather than commenting the Classics by themselves in order to find a supposed philological or textual thruth. Reading is reinventing; texts are "open". Secondly, to the building of a unified understanding of the canonical texts that could be coherent with the Neo-Confucian educative and didactic project. Reading is finding new ways of behaviour; texts are pretexts. This point leads us to bring up the third and last attitude toward the canonical texts, which corresponds with the longest distance taken from the texts: the massive and seminal use of diagramms. Diagramms have often been used by scholars since the very reception of Neo-Confucianism in Korea to present an overall and systemic view of Neo-Confucian thought. The most famous examples are Kwŏn Kŭn's Iphak tosŏl 入學 圖說 and T'oegye's Sŏnghak sipto 聖學十圖. As for the Sŏnghak chipyo 聖學輯要 of Yulgok, which consists in a compilation of quotations from the Classics and Neo-Confucian commentaries with some personnal comments of the author about the socalled Learning of the Sovereign (chehak 帝學), it can be said that the very construction of the whole work is a meaningful architecture, illustrated by Yulgok himself in a diagramm. Resorting to schematical and synoptical presentation is revealing once again the didactic concern of the first Korean Neo-Confucian scholars, in quest for coherence and unity. I would like to allude now to the topic of the goal of reading and commenting canonical texts at the beginning of Chosŏn. As has been shown just before, the different standpoints or distances taken from the texts by kings and scholars are all denoting the same concern for unity and education.

"

  If the heart does not exercize and the body does not act according to what the mouth is reciting, what would be the benefit of a book remaining a book, and me remaining myself ?" (若口讀而心不體身不行, 則書自書我自我. 何益之有。KMYG 4).The major expression of this concern for education, unification and more broadly for the confucian project taken as a civilizing process can be found in the spread of textbooks dealing with the samgang 三綱 (父子有孝, 君臣有忠, 夫婦有烈) and the oryun 五倫 (長幼有序 and 朋友有信 added to the samgang). In the 15th and 16th centuries, many compilations on this topic have been produced under royal commands or by scholars' personnal initiatives -like Kim Anguk 金安國 (1478-1543) writing the yiryŏn haengsildo 二倫行實圖 (1518). Let's also mention here the Samgang haengsildo 三綱行實圖 (1481), the Sok samgang haengsildo 續三綱行實圖 (1514 and 1581), the Yiryun haengsildo 二倫行實圖 (1579) and the Oryun nok 五倫錄 written under Sejo's reign (1455-1468). These texts -that are not exactly commentaries of Classics and Neo-Confucian literature though -are aiming at incalculating basic moral values in order to implement good morals and law and order. The same is true of the handbooks and others concise guides summarizing Neo-Confucian principles and rules that the Korean Confucian scholars have been writing from the 16th century on, as educatives tools 2009 AKSE Conference -7 -reinforcing the creation and developement of academies, sŏwŏn 書 院 , as well as community compacts, hyangyak 鄉 約.By way of conclusion, I would like to underline the impact of the historical context of the 14th to the 16th century, which has been the stage of a permanent tension between the two poles of political power: the kings and the elites. One aspect of this tension is the control over enacting a coherent educational policy and building a unified body of knowledge. Besides, I would also like to stress the interest of considering philosophical exegeses as reflects, products or, conversely, as the driving force behind the changes in, for example, 1) the perception of the Canon taken as texts -texts that are open to commentaries but tending inevitably to get enclosed in an orthodox version -, 2) the strenghtening of Master-disciples relationships that enriched exegetical practices by providing a common life only dedicated to Learning in structures like Confucian academies, 3) the creation of the figure and the identity of the Confucian litteratus -the emblematic Korean sŏnbi -understood as an "intellectual" rather than an administrator.


Théophile Baudry

Mickael Causse

Cédric T Albinet

Performing a cognitive task with different levels of: -Difficulty (working memory load) -Executive involvement

published or not. The documents may come

Introduction Method

The Switching paradigm:

Letter/Digit tasks

Results

Discussion

Participants' behavioral performance was affected by both task difficulty and the involvement of executive control (flexibility). Moreover, the increasing of task difficulty tended to reduce the switch cost on RT, a result sometimes reported in the literature.

Both sympathetic (PEP) and parasympathetic (HF power, RMSSD) activities increased during the executive task (flexibility) but were not affected by task difficulty. To the best of our knowledge, it is the first report of such a pattern of results using a within-subject design. This design may help to better understand the discrepant results in the literature. These results may suggest that cardiac reactivity might reflect more executive control than higher effort per se. Future studies must replicate these findings and control baseline resting cardiac activity as well as time on task effects to ascertain this conclusion. Monsell (1995)

  Richter, M., Friedrich, A., & Gendola, G.H.E. (2008). Psychophysiology, 45, 869-875. Rogers, R.D., & Monsell, S. (1996). Journal of Experimental Psychology: General, 124(2), 207-231. Sherwood, A., Allen, M.T.,…,& Van Doornen, L.J.P. (1990). Psychophysiology, 27(1), 1-23. Thayer, J.F., & Lane, R.D. (2009). Neuroscience and Biobehavioral Reviews, 33, 81-88. Wright, R.A., & Gendolla, G.H.E. (2012, Eds.). How motivation affects cardiovascular response. Mechanisms and applications. Washington DC: APA. Participants Significant effect of Difficulty (p < .0001): Easy < Medium = Difficult. Significant effect of Block (p < .0001): Simple block < Mixed block. Significant Difficulty X Block interaction (p < .0001) Significant effect of Block (p < .005): Simple block < Mixed block. No effect of Difficulty. No interaction. Results virtually identical for RMSSD. The percentage of correct responses was high (> 90%) and overall higher for the Easy condition than the two other conditions. Significant effect of Block (p < .005at rest and during cognitive activity -HRV: parasympathetic activity = HF power and RMSSD of R-R intervals -PEP: sympathetic activity 35 healthy students (26 females); 18-26 years. Body Mass Index: 16.5-27.4 (m = 21.5) Syst. Blood Pressure: 84.5-134 (m = 107) Diast. Blood Pressure: 50-75.5 (m =60) PEP Objective: To examine whether cardiac reactivity is related to task difficulty or to executive control using a within-subject experimental design. adapted from Rogers &

Wright & Gendolla (2012); Richter et al. (2008) Sherwood et al. (1990); Thayer & Lane (2009)


Isabelle Sancho

"Yulgok and the Neo-Confucian Civilizing Process: Old Wine in a New Bottle?"

The active participation of Yulgok, Yi I (1536-1584) in the implementation of Neo-Confucianism in the second half of the 16 th century is a commonly agreed historical assumption, notably because of his well-known involvement in 1) Confucian academies, 2) community compacts, 3) collective granary, 4) private school, not to mention his administrative writings and private initiatives within his own family. Detailing his practical involvement in social programs will not be the topic of my talk. Continuing a reflection started at the 2007 AKSE Conference in a panel also focused on the Confucianization of Korea, my aim is rather to try to understand this civilizing project and process from the inside, that is to say, by trying to understand Yulgok's mental and intellectual framework. I will limit my talk today to a few theoretical questions that are deeply linked to the very notion of 'civilizing process' (kyohwa 教化 or hwa 化) in Neo-Confucianism and in Yulgok's texts as well, in order to shed a new light on this problem in the context of 16 th century Korea.

Historical context

For most of the 16 th century scholars-officials, their times were that of crisis and degeneration, synonymous with the end of a cycle started with the new dynasty. Especially, the successive and bloody literati purges of the 15 th and 16 th centuries have been a traumatic experience that left the elites puzzled about their own identity and social role.

They have revealed that something went wrong in the exercise of power and the conduct of state affairs. So most of the Confucian scholars, holding a position or not, were calling for reforms. As for Yulgok, he made a straightforward and simple statement of fact on several occasions (civil service examinations' dissertations, Tongho mundap 東湖問答, Sŏnghak chipyo 聖學輯要, memoranda): that the State is ailing (pyŏng 病) and need to be 'cured' properly (ch'i 治; which also mean 'to govern'). The treatment to the illness is Confucianism. More precisely, Confucian civilizing influence (yup'ung 儒風) and Confucian behaviors and practices (yusŭp 儒習 or sasŭp 士習) must be restored among scholars as well as at court. So, although the civilizing process ideally concerns the whole society, it must be beforehand prepared by the proper cultivation of the two poles of political power: the king and the elites. Civilizing common people is of course on the agenda, as the normative measures taken in various fields in the 16 th century clearly show, but this is not the top priority for Yulgok and his peers.

A specific conception of time and history in Neo-Confucianism

To better understand this, let us remind the conception of time and history in Neo-Confucianism. As it is well-known, one core notion in Neo-Confucianism is the Tot'ong 道通, the 'Transmission of the Way'. The ideal government and society are believed to have existed in old antiquity, although this antiquity is so remote that it seems almost ahistorical. This model of sagely kingship (called sŏnwang chi to 先王之道, chewang chi ch'i 帝王之治, wangdo chi hak 王道之學, ingun chi hak 人君之學) sets a precedent in human history, which reasserts confidence in the potentiality of mankind.

Besides, it is worth noticing that this precedent has been set by men, such as the sagacious emperors Yao and Shun. In Neo-Confucian theory, the course of history should be driven by outstanding men, called 'Sages' (sŏngin 聖人), whose hallmark is their having fully achieved their human potentiality in perfect accordance with the cosmic order. The most important element in the Transmission of the Way is less the Way itself than those providential men who are able to embody, transmit and bring up to date the ideal of civilization. However, according to the Neo-Confucian cosmology, an unavoidable degeneration is also part of the natural cosmic order as time goes by, mainly because of the evolution and deterioration of the Material force (Ki 氣). This means that the civilizing process can hardly be achieved definitely. The kyohwa could then be defined as a permanent work in progress, and it turns out to be a recurring project that calls for constant and repeated efforts. To put it in a nutshell, the ethical practice that is at the heart of the Neo-Confucian notion of civilization is basically inscribed in a complex temporality, related to both the cosmic and human orders. There is indeed the temporality of one single individual's ethical practice, which is in turn intimately linked to the temporality of the historical trajectory of the whole society.

Yulgok's viewpoint on the history of civilization in Korea and China

As for Korea, Yulgok provides an interesting viewpoint on the beginnings of civilization, focusing on one single man: Kija/Qizi 箕子, revered in both Chinese Henan and Korean P'yŏng'ando. According to Yulgok, Kija was the common ancestor of Chinese and Korean historical civilized states (wŏnsŏng 元聖), for he had given the forgotten secret of the mythical emperor Yu the Great, the Hongfan/Hongbŏm 洪範, to Wu of Zhou before leaving for the Korean peninsula. Kija is said to have deliberately fled China, for he was opposed to the new dynasty founded by brutal force. His descendants then created in Korea an independent state (kuk 國), shaped with affection and benevolence, and civilization started to flourish in Korea. The main feature of Kija's civilizing influence stressed by Yulgok is his governing by rites and ethics, in a time far before Confucius. In

Yulgok's diagnosis of late 16 th century Korea

Besides, in his famous Tongho mundap, a royal command written during his sabbatical leave at the Toksŏdang, Yulgok presented some ideas that are emblematic of his diagnosis of the contemporary situation. As I said, Yulgok considered that the country was sick because of the general lack of concern for a correct practice of Confucianism. But his most important argument is related to his deep belief in one locus classicus characterizing the Korean reception of Neo-Confucianism in the first half of Chosŏn: chŏngsim 正心, the rectification of mind. In its Korean understanding, this notion underlines the necessary interaction between kings and ministers. In his Tongho mundap, Yulgok notably explains that Kija's family founded for the first time a civilized state in Tangun's ancient territory.

As for Koryŏ, the state failed to rule the country, for it was misled by Buddhism. After that, the new Yi dynasty was founded by men claiming to be the heirs of Kija Chosŏn and who thus wanted to use the right ideology: Confucianism. But in spite of their good will, Chosŏn kings and administrative elites have always failed, because of their misunderstanding and lack of sincere interaction. Rectifying the king's mind, which enables to rectify the court's mind and civilize the country is basically the task of the Confucian scholars-officials. Even though the civilizing process is theoretically in the hands of the king, the real driving forces and leaders are believed to be the Confucian elites, who must care for the implementation of the correct kingship as well as for the happiness of the whole society. By arguing that Confucian kingship is the cornerstone of an ideal state and society, Korean scholars-officials have paradoxically developed a very specific rhetoric about the balance of power where they are portrayed as equal to kings.

For instance, Yulgok explains that king Sejong didn't succeed in practicing the Way in spite of his outstanding abilities, for he had lacked good ministers to help him. So the civilizing process can't be launched without this human encounter between a good prince and good minister. But this encounter is basically a matter of chance and can't be controlled. Thus, the civilizing process is tributary to the complexity of human interplays and it is a dynamics based on changing human relationships but also emotions.

The cosmology of the Book of Changes

One might wonder how it could be possible to perpetuate and deal with something that is subject to constant shifts. This question precisely points to the very heart of the Neo-Confucian Weltanschauung: the problematic of the Changes. When tackling with the problem of the civilizing process, one cannot escape thinking about the meaning and impact of the cosmology of the Book of Changes. As aforementioned, the civilizing process follows a dual sense of temporality, which raises also the question of the dialectics of duration (ku 久) and moment (si 時). The Neo-Confucian questioning is mainly preoccupied with how to bring and maintain constancy in a world regarded as ceaseless changes. This idea is conveyed for instance in a constellation of key concepts such as sang 常, yung 庸, t'ong 通, but also chŏng 定 and chi 止 that appear especially in the Doctrine of the mean or the Great Learning, the foundational texts for the Neo-Confucian "civilizing process". Although civilization was realized in old antiquity, such a harmonious state couldn't last long, and although civilization might be about to be realized again, it will be difficult to make it last forever. The task seems almost impossible, for it depends on human interactions and what we would call 'hazard' or 'chance'. But the cosmology of the Book of Changes precisely provides a solution to the problem. This philosophy is indeed grounded on the trust that the world is fundamentally understandable by the human mind, and that there is some kind of rationality going on under the surface of changes (the idea of Principle, Yi 理). Moreover, in a world regarded as a sort of huge magnetic field, human beings can resonate with and be part of the cosmic process. Rather than talking about 'chance' or 'hazard', the exegesis of the Book of Changes and Neo-Confucian texts use the term myŏng 命, 'destiny' or 'fate', which basically designates the right match (ŭi 義) with the cosmic order. In other words, the cosmology of the Changes provides the intellectual tools guaranteeing that human order can actually be achieved through the perfect and correct conformity with the natural order. Hence the problem only lies in the correct understanding (knowledge, chi 知) and the proper ethical practice (praxis, haeng 行) that are both needed in order to ensure this conformity with the natural order. So the civilizing process is believed as feasible through proper ethical practice.

The civilizing process: hwa 化, pyŏn 變 and Ki 氣

Let us now examine briefly a few notions taken from the Book of Changes and his exegesis. Changes, yi 易, is the generic term designating the transformation or change. But the most important notions are certainly hwa 化 and pyŏn 變. Pyŏn means a change in the nature of one line of a hexagram: the transformation from a yin line to a yang line, or conversely from yang to yin. Hwa means on the contrary the continuous and progressive transformation without any change of nature. Hwa is indeed related to the notion of continuity, t'ong 通. When talking about Kija, Yulgok says that he transformed the barbaric Koreans into civilized people: pyŏnyi 變夷, which means that he had changed their nature. After that, the sage kingship perpetuated by his descendants over many centuries is described as a "sage transformation", sŏnghwa 聖化. Moreover, this transformation, hwa, is characterized by a few signs that remain and are still perceptible, although they are very thin. What is worth underlining here is this idea of something remaining and still perceptible (yuhun 遺訓,yup'ung 遺風). So the civilizing process, started with Kija, may be reactivated thanks to those remaining signs. More precisely, because those signs are perceptible, the "mind" (sim 心) of the civilizing sovereigns of antiquity may be activated again through the mind of their followers, that is to say the Confucians. That is why the Transmission of the Way is understood in orthodox Neo-Confucianism as the transmission of the mind of the Sages. Besides, according to Yulgok, what enables the reactivation of this mind is the Material force, the Ki 氣 that pervades the world past and present, and that rules the mind of every man. Yulgok's philosophical reflection on the Ki is very well-known in intellectual history, and this interest certainly illustrates his reflection on how the Confucian Way could be put into practice. Indeed, cultivating the Ki is part of the ethical training of Confucian scholars. Moreover, the scholars-officials are the "fundamental energy", wŏnki 元氣, of the country. So it can be said that the sake of the whole society mainly depends on them as well as their correct ethical training.

Conclusion

By way of conclusion, I would like to raise a few related questions. Firstly, although it is commonly argued that Yulgok's political thought is focused on the people's well-being (minbon chŏngch'i 民本政治), most certainly in order to set him up as an icon of Korean 'national spirit', I can't help but wonder whether his thought is, above all, shaped by his self-interests. Of course his activism (as a high official and also as a Confucian master) in implementing Confucian values, practices and norms cannot be denied. But what is striking in his life and thought is that his perspective basically remains moral. The Confucian civilizing process is an ethical project primarily meant for himself (it is a Learning, hak 學) and, by extension, for his own social group. So the civilizing mission might be seen as a means mainly intended to legitimate both the social and existential raison d'être of the Chosŏn scholars-officials at the end of the 16 th century. Secondly, I wonder whether his use of Kija could not be seen as a good illustration of this selfcentered viewpoint. Indeed, Kija was not a sovereign in China and he did not establish himself a kingdom in Korea. He is rather the paragon of the loyal and exemplary 'minister' who, after many ups and downs in China, ended up creating a civilized society in Korea, remaining faithful to his quest for benevolence and virtue. So the model and precedent of civilization described by Yulgok for Korean history is set by a minister, not an emperor or a king. I am thus wondering whether this is not an implicit praise of self-made Confucians, that is scholars-officials, rather than monarchs by birth. Last but not least, one cannot deny that Yulgok suffered from deep disarray-traumatic soul searching-because of his high sense of moral and social commitment to the Confucian Way. I do believe that this aspect could be fruitfully studied further in future scholarship when considering Confucian scholars' attitude towards the civilizing process.

  his long description of the history of the Ki family's rule in Korea, Yulgok contrasts the peacefulness and the ethical practices and mindsets of Korean people with the instability, violence and guile of contemporary Chinese people of the period beginning with the Warring States. The hazards and the final collapse of the Ki family's successive kingdoms of Kija Chosŏn and Mahan, after more than a thousand years of sagely rule, are mainly due to the chaos generated by the troubled Chinese history. To sum up, from 1568 when he first wrote a text on Kija (Kijachŏn 箕子殿), Yulgok developed little by little a specific discourse on civilization and the Confucian Way in various texts (Sŏnghak chipyo, Kija silgi, Ch'a Wangch'ŏnsa Kija myo buun). He notably used the figure of Kija to demonstrate the coincident beginnings of the Confucian Way in China and Korea, and he even suggests that Kija's Korea was far better than China.