Neutral particle Mass Spectrometry with Nanomechanical Systems

Current approaches to Mass Spectrometry (MS) require ionization of the analytes of interest. For high-mass species, the resulting charge state distribution can be complex and difficult to interpret correctly. In this article, using a setup comprising both conventional time-of-flight MS (TOF-MS) and Nano-Electro-Mechanical-Systems-based MS (NEMS-MS) in situ, we show directly that NEMS-MS analysis is insensitive to charge state: the spectrum consists of a single peak whatever the species charge state, making it significantly clearer than existing MS analysis. In subsequent tests, all charged particles are electrostatically removed from the beam, and unlike TOF-MS, NEMS-MS can still measure masses. This demonstrates the possibility to measure mass spectra for neutral particles. Thus, it is possible to envisage MS-based studies of analytes that are incompatible with current ionization techniques and the way is now open for the development of cutting edge system architectures with unique analytical capability

Hippo pathway effectors YAP1/TAZ induce an EWS–FLI1‐opposing gene signature and associate with disease progression in Ewing sarcoma

YAP1 and TAZ (WWTR1) oncoproteins are the final transducers of the Hippo tumor suppressor pathway. Deregulation of the pathway leads to YAP1/TAZ activation fostering tumorigenesis in multiple malignant tumor types, including sarcoma. However, oncogenic mutations within the core components of the Hippo pathway are uncommon. Ewing sarcoma (EwS), a pediatric cancer with low mutation rate, is characterized by a canonical fusion involving the gene EWSR1 and FLI1 as the most common partner. The fusion protein is a potent driver of oncogenesis, but secondary alterations are scarce, and little is known about other biological factors that determine the risk of relapse or progression. We have observed YAP1/TAZ expression and transcriptional activity in EwS cell lines. Analyses of 55 primary human EwS samples revealed that high YAP1/TAZ expression was associated with progression of the disease and predicted poorer outcome. We did not observe recurrent SNV or copy number gains/losses in Hippo pathway‐related loci. However, differential CpG methylation of the RASSF1 locus (a regulator of the Hippo pathway) was observed in EwS cell lines compared with mesenchymal stem cells, the putative cell of origin of EwS. Hypermethylation of RASSF1 correlated with the transcriptional silencing of the tumor suppressor isoform RASFF1A, and transcriptional activation of the pro‐tumorigenic isoform RASSF1C, which promotes YAP1/TAZ activation. Knockdown of YAP1/TAZ decreased proliferation and invasion abilities of EwS cells and revealed that YAP1/TAZ transcription activity is inversely correlated with the EWS–FLI1 transcriptional signature. This transcriptional antagonism could be explained partly by EWS–FLI1‐mediated transcriptional repression of TAZ. Thus, YAP1/TAZ may override the transcriptional program induced by the fusion protein, contributing to the phenotypic plasticity determined by dynamic fluctuation of the fusion protein, a recently proposed model for disease dissemination in EwS

Frequency fluctuations in silicon nanoresonators

Frequency stability is key to performance of nanoresonators. This stability is thought to reach a limit with the resonator's ability to resolve thermally-induced vibrations. Although measurements and predictions of resonator stability usually disregard fluctuations in the mechanical frequency response, these fluctuations have recently attracted considerable theoretical interest. However, their existence is very difficult to demonstrate experimentally. Here, through a literature review, we show that all studies of frequency stability report values several orders of magnitude larger than the limit imposed by thermomechanical noise. We studied a monocrystalline silicon nanoresonator at room temperature, and found a similar discrepancy. We propose a new method to show this was due to the presence of frequency fluctuations, of unexpected level. The fluctuations were not due to the instrumentation system, or to any other of the known sources investigated. These results challenge our current understanding of frequency fluctuations and call for a change in practices

Conception, fabrication, caractérisation de micromembranes résonantes en silicium, à actionnement piézoélectrique et détection piézorésistive intégrés appliquées à la détection d'agents biologiques simulant la menace.

The threat of a massive and lethal biological attack aiming at armies or civilians has compelled military research institutions to invest massively in planning the response to such an attack. The response to a biological attack is contingent to abilities of perception and identification of this attack. Therefore, the need of low-cost, reliable, easily transportable, biological detection solutions is crucial. In this manuscript, we study the cases of biosensors based on silicon resonant micro-membranes, fabricated by standards micro-fabrication techniques. We first emphasize the advantages of these types of sensors to fill the requirements of the studied problematic. Then, according to initial objectives expressed in term of mass resolution and sensitivity, we report the theoretical study enabling the sizing and design of micro-membranes in order to satisfy these requirements. The global detection principle is dynamic micro-gravimetry. The vibration of membranes is provided through the action of a piezoelectric patch deposited on top of the membranes, the vibration detection is operated by piezoresistances located at micro-membranes' clamping. We report the micro-systems fabrication, their packaging and the fabrication of associated detection electronics. Finally, the electrical, electro-mechanical and biological characterization enables the focus on main results obtained during this work with respect to state of the art. First point lies in the demonstration of a physical co-integration of piezoelectric and piezoresistive phenomena inside a same resonating microstructure for biosensing applications. On a second hand the ability to track in real time the resonant frequency of several multiplexed micro-membranes vibrating in a liquid media provided to piezoresistive detection of vibration is reported. At last, results obtained for detection of biological warfare agents' surrogates are presented.La menace d'une attaque bactériologique massive et létale visant les armées ou les populations civiles ont obligé les institutions de recherche militaire à investir massivement dans la préparation à une telle éventualité. La réponse à donner à une attaque bactériologique est conditionnée par les capacités de perception et d'indentification de cette attaque. Ainsi, le besoin en solution de détection et de reconnaissance biologique fiables, peu chères, facilement manipulables est crucial. Nous abordons dans ces travaux de thèse le cas de biocapteurs basés sur des micromembranes résonantes en silicium, assemblées par des technologies de microfabrication classiques. Nous montrons tout d'abord les avantages comparés de ce type de capteur pour répondre à la problématique donnée. Puis, nous rapportons l'étude théorique permettant le dimensionnement des micromembranes en fonction d'objectifs initialement formulés en termes de sensibilité et de limite de détection. La mise en vibration des membranes est assurée par l'action d'une pastille piézoélectrique déposée sur sa surface, la détection du mouvement est effectuée par une jauge piézorésistive positionnée à l'encastrement de la membrane. Nous abordons par la suite, la fabrication du microsystème, son conditionnement ainsi que la fabrication de l'électronique de détection associée. Enfin la caractérisation électrique, mécano-électrique puis biologique des membranes nous permet de mettre en relief les principaux résultats obtenus par rapport à l'état de l'art. Le premier point réside dans la démonstration de la co-intégration physique des phénomènes piézoélectrique et piézorésistif au sein d'une même structure résonante. Est démontrée ensuite la capacité à suivre en temps réel la fréquence de résonance des membranes par détection piézorésistive, lorsque celles-ci sont immergées dans un milieu biologique aqueux. Pour terminer, les résultats biologiques quant à la détection d'agents simulant la menace biologique sont présenté

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

Electrical equivalent circuit for air and liquid characterization of a multilayer micromembrane with piezoelectric actuation and read-out capabilities

International audienceDuring the last decade, piezoelectric-based microresonators have shown a great interest in the micro electromechanical systems (MEMS) field, especially for biosensing applications. Micromembranes have revealed a particular potential for biological experiments [1]. In order to optimize their design, the analytical modeling of their dynamic behavior is of critical importance. We report the elaboration of an analytical model for the case of a micromembrane with piezoelectric actuation and detection vibrating either in air or in a viscous fluid. The model, based on an equivalent electrical circuit, enables the computation of specific characteristics like mass sensitivity, resonance frequency and minimum detectable mass. The model was established for a five-layer stack membrane with a circular lead zirconate titanate 46/54 PbZrxTi1-xO3 (PZT) active cell (Fig 1). The method was based on the separation of the membrane's electromechanical behaviour into three parts. First, a purely mechanical transfer function, linking the force exerted on the membrane by the piezoelectric layer to the relative displacement of the membrane, was determined[2]. Then, the actuation coupling coefficient was determined by relating the applied voltage and moment applied to the membrane [3]. Finally, the sense electromechanical coupling coefficient is found linking the deflection of the membrane and the resulting charge creation at output electrode. The global admittance, resulting from the merging of the three previous parameters corresponds to an equivalent electrical circuit modeling the vibrations of the piezoelectric membrane in air. We also realised the implementation of the model for the case of vibration in a viscous fluid by adding two extra equivalent electrical components modelling the effects of the surrounding fluid (a.k.a fluidic resistance and inductance) respectively corresponding to the damping and added mass induced by the fluid. The final equivalent electrical circuit allows the determination of theoretical values for the membranes' characteristics as biosensors. The fabrication process has been described in details elsewhere [4] and a top view of a membrane's chip is shown on fig 2. The dynamic behaviours of fabricated membranes, with a 100 µm global radius and piezoelectric cell radius of 30, 50 and 70 µm, have been extracted experimentally. The curves for real and imaginative part of the complex admittance were obtained with a HP4294A impedance analyzer. The comparison between experimental and theoretical behaviour is reported for the three types of membranes and good agreement between the theoretical experimental curves is observed for the case of vibrations in air (Fig 3). In the case of operation in fluid, good accordance in amplitude is observed even though a constant shift in frequency (8%) between theoretical and experimental values still remains as shown on fig 4. Work is now under progress to compare the theoretical and the experimental mass sensitivity and minimum detectable mass of the membranes in real biological assays

Investigation of molecularly imprinted polymers to detect proteins by an integrated, autonomous piezoelectric micro membranes platform

International audienc

Investigation of molecularly imprinted polymers to detect proteins by an integrated, autonomous piezoelectric micro membranes platform

International audienc