Complete Set of Elastic Moduli of a Spin-Crossover Solid: Spin-State Dependence and Mechanical Actuation

Molecular spin crossover complexes are promising candidates for mechanical actuation purposes. The relationships between their crystal structure and mechanical properties remain, however, not well understood. In this study, combining high pressure synchrotron Xray diffraction and nuclear inelastic scattering measurements, we assessed the effective macroscopic bulk modulus (11.5 ± 2.0 GPa), Young’s modulus (10.9 ± 1.0 GPa) and Poisson’s ratio (0.34 ± 0.04) of the spin crossover complex [FeII(HB(tz)3)2] (tz = 1,2,4-triazol-1-yl) in its low spin state. Crystal structure analysis revealed a pronounced anisotropy of the lattice compressibility, which was correlated with the difference in spacing between the molecules in different crystallographic directions. Switching the molecules from the low spin to the high spin state leads to a remarkable drop of the Young’s modulus to 7.1 ± 0.5 GPa, which was also assessed in thin film samples by means of micromechanical measurements. These results are in agreement with the high cooperativity of the spin crossover in this compound and highlight its application potential in terms of recoverable stress (21 ± 1 MPa) and work density (15 ± 6 mJ/cm3)

BioMEMS pour l'Analyse Biomoléculaire : de l'intérêt du confinement et de la réduction d'échelle pour la quantification directe de biomarqueurs

National audiencePersonalized medicine holds the promise to greatly improve patient well-being and to lower the overall cost of medical care. To make this happen, there is an urge to develop new biosensing platforms for the absolute quantification of biomarkers in liquid biopsies with high sensitivity, specificity, portability and at a low cost. This thesis presents the technological toolbox that I have been developing during the last 10 years at LAAS-CNRS to try and provide new molecular analysis devices. More specifically, I propose solutions that take advantage of the size reduction inherent to bioMEMS: nanofluidics-embedded biosensors for kinetic study of molecular interactions, resonant MEMS biosensors for label free detection, and porous silicon membranes for on-chip sample preparation based on filtering and ion concentration polarization.Afin de permettre l’avènement de la médecine personnalisée et les promesses qui l’accompagnent en terme notamment d’amélioration de la prise en charge des patients et de baisse des coûts des soins médicaux, il est nécessaire de développer de nouveaux dispositifs de dosage moléculaire permettant de démocratiser les analyses à partir de prélèvements non-invasifs (biopsies liquides).Les technologies issues de la microélectronique ont fait naitre une grande variété de biocapteurs, sous la forme de dispositifs à haut degré d’intégration offrant des avantages indéniables par rapport aux techniques d’analyses moléculaires classiques : détection sans marquage, quantification directe des biomolécules, préparation d’échantillon minimale et rendu des résultats accéléré. Ce sont précisément ces avantages, liés à une technologies potentiellement bas coût, multiplexe, et portable qui entretiennent la promesse d’avoir accès à des analyses routinières au chevet du patient, calquée sur le modèle de réussite des appareils de mesure du glucose pour les personnes diabétiques.Mes activités de recherche conduites au LAAS ces 10 dernières années sont axées sur l’utilisation des microtechnologies pour l’analyse moléculaire en traitant les différentes composantes d’un biocapteur : développement de moyens de transduction, de stratégies de biofonctionnalisation et outils pour la préparation d’échantillon. Plus spécifiquement, mes travaux visent à tirer parti de la réduction de taille et du confinement spatial inhérents aux bioMEMS : plateforme nanofluidique pour l'étude cinétique d’interactions moléculaires, intégration de membranes de silicium poreux dans des systèmes fluidiques planaires pour la réalisation d’étapes pré-analytiques sur puce, et recours aux MEMS résonants pour la détection sans marquage

Bioplume : a MEMS-based picoliter droplet dispenser with electrospotting means for patterning surfaces at the micro- and the nanometer scales

The interest in patterning surfaces with micro- and nanometer resolutions has been growing fast in recent years, illustrating the tremendous potential of patterning techniques for both fundamental investigations and technological applications in photonics, molecular electronics, and biosensors. Among the various patterning methods, liquid dispensing techniques relying on the use of microcantilevers are very promising for several reasons. The first one is that they permit a direct patterning of the surface with different kinds of materials without any need for prefabricated patterns. Secondly, alignment of the cantilevers with respect to specific regions on the surface is straightforward since the cantilevers themselves can be used as displacement sensors. Moreover, parallel approaches can be developed to meet specific requirements in terms of throughput and fabrication costs. In this thesis we present a liquid spotter (so-called Bioplume) based on the use of silicon microcantilevers. Droplets are formed on the surface by a direct contact method. The fabricated cantilever array is integrated to a closed-loop automated system allowing the control of the droplet homogeneity and the spatial positioning of the microarray. The system relies on the use of force sensors, i.e. piezoresistors, integrated into the cantilevers to adjust the trim and to control the deposition parameters, i.e. contact force and time. By using a specific external loading chip, different liquids can be loaded onto the cantilevers, enabling the parallel deposition of several entities in a single deposition run. Besides, an electrode is incorporated in the channel to allow using electrowetting and electrochemistry. The former is used to actively load the cantilever and to control the drop size during delivery, while the latter is used to drive electrochemical reactions in the deposited picoliter droplets. This tool has been used to print biological solutions, to electrodeposit copper, to electropolym erize functionalized pyrrole and to directly create crystalline microspots of nanobeads. The control of the printed features (resolution, thickness, and composition), the versatility of the printed materials and the added electro-assisted features demonstrate the tremendous potential of the Bioplume tool for research work and industrial applications.Les techniques de structuration et de fonctionnalisation de surfaces aux échelles micro- et nanométriques connaissent un intérêt croissant lié aux possibilités qu'elles offrent pour l'étude des phénomènes fondamentaux à faible échelles et aux avancées technologiques qu'elles permettent dans les domaines de l'électronique, de la photonique et de la bio-ingénierie. Parmi les nombreuses techniques qui ont été développées durant les dernières décennies, les méthodes reposant sur l'utilisation de microleviers pour le dépôt de faibles volumes de liquide offrent, entre autre, l'avantage d'être directes et parallélisées, et sont particulièrement adaptées aux applications biologiques. Les travaux présentés dans cette thèse portent sur la conception et la réalisation d'un système de dépôt de gouttes micrométriques à l'aide de matrices de leviers en silicium. L'originalité de ce système, nommé Bioplume, repose sur l'intégration de capteurs de forces et sur l'utilisation de méthodes de dépôt assistées par champ ou par auto-assemblage pour contrôler in-situ la taille, l'uniformité et la composition des motifs réalisés. Le système fonctionne en boucle fermée afin d'automatiser la fabrication de micromatrices de spots tout en garantissant la correction des erreurs d'alignement et le contrôle de la force exercée et du temps de dépôt. Après avoir validé le chargement assisté par électromouillage et le dépôt de solutions biologiques, nous utilisons les phénomènes d'auto-organisation afin de créer directement, à partir de solutions de nanoparticules, des microspots cristallins. Enfin, à l'aide d'électrodes incorporées aux leviers, des réactions électrochimiques sont induites dans les volumes de liquides déposés (de l'ordre du picolitre), permettant l'électrodéposition de cuivre et l'éléctropolymérisation de pyrroles. Les nombreuses fonctionnalités apportées à ce système pendant cette thèse permettent d'étendre ses capacités, faisant de Bioplume une solution fiable et complémentaire au x techniques de jet d'encre et de dip-pen en terme de taille de motifs

Fabrication of lateral porous silicon membranes for planar microfluidics by means of ion implantation

International audienceWe introduce a new fabrication method based on ion implantation to create lateral porous silicon membranes and integrate them into planar microfluidic devices. Our proposed method relies on the fact that the formation of porous silicon by anodization highly depends on the dopant type and concentration, which can be manipulated by ion implantation. In order to confine the porosification at desired locations within silicon steps bridging microchannels, we use boron and phosphorus implantation to respectively create a p++ layer buried in an n-type silicon substrate, and a protective n-type surficial layer. The use of a metal electrode patterned onto the silicon step for current injection during anodization enables pores to propagate laterally during the membrane formation. The optimal implantation doses and energies leading to the required boron and phosphorus profiles are determined by means of process simulation and further confirmed by SIMS analysis. We demonstrate that the proposed fabrication process leads to the creation of lateral porous silicon membranes with open-ended pores adequately bridging microchannels and that we are able to manipulate the pore size (∼3–30 nm) and membrane porosity (∼15–65%) by adjusting the current density during anodization. The adequate dead-end filtration capability of the fabricated membranes was tested and demonstrates the interest of the presented fabrication process for microfluidic applications

A micromachined resonant magnetic field sensor

M.S.Mark G Alle

Integration of lateral porous silicon membranes into planar microfluidics

International audienceIn this work, we present a novel fabrication process that enables the monolithic integration of lateral porous silicon membranes into single-layer planar microchannels. This fabrication technique relies on the patterning of local electrodes to guide pore formation horizontally within the membrane and on the use of silicon-on-insulator substrates to spatially localize porous silicon within the channel depth. The feasibility of our approach is studied by current flow analysis using the finite element method and supported by creating 10 μm long mesoporous membranes within 20 μm deep microchannels. The fabricated mem-branes are demonstrated to be potentially useful for dead-end microfiltration by adequately retaining 300 nm diameter beads while macromolecules such as single-stranded DNA and immunoglobulin G permeate the membrane. The experimentally determined fluidic resistance is in accordance with the theo-retical value expected from the estimated pore size and porosity. The work presented here is expected to greatly simplify the integration of membranes capable of size exclusion based separation into fluidic devices and opens doors to the use of porous silicon in planar lab on a chip devices

Des aimants miniatures fabriqués à partir de nanoparticules

National audienc

Towards circulating microRNA detection using fluorescence-based nanofluidic platform for the early diagnosis of pancreatic cancer

International audienc

Des aimants miniatures fabriqués à partir de nanoparticules

National audienc

MEMS Biosensors and COVID-19: Missed Opportunity

International audienceThe acceleration of climatic, digital, and health challenges is testing scientific communities. Scientists must provide concrete answers in terms of technological solutions to a society which expects immediate returns on the public investment. We are living such a scenario on a global scale with the pandemic crisis of COVID-19 where expectations for virological and serological diagnosis tests have been and are still gigantic. In this Perspective, we focus on a class of biosensors (mechanical biosensors) which are ubiquitous in the literature in the form of high performance, sensitive, selective, low-cost biological analysis systems. The spectacular development announced in their performance in the last 20 years suggested the possibility of finding these mechanical sensors on the front line of COVID-19, but the reality was quite different. We analyze the cause of this rendez-vous manqué, the operational criteria that kept these biosensors away from the field, and we indicate the pitfalls to avoid in the future in the development of all types of biosensors of which the ultimate goal is to be immediately operational for the intended application