micro-RNA 21 detection with a limit of 2 pM in 1 min using a size-accordable concentration module operated by electrohydrodynamic actuation

International audienceWe present a fluorimetry-based technology for micro-RNA-21 (miR-21) sensing based on the concentration of miR-molecular beacon (MB) complexes and flushing of unbound MB. This concentration module consists of a microfluidic channel with the shape of a funnel operated with electrohydrodynamic actuation. We report a limit of detection of 2 pM in less than one minute for miR-21 alone, and then demonstrate that miR-21 levels measured in fine needle biopsy samples from patients with pancreatic cancer correlate with the reference technique of reverse-transcription polymerase chain reaction (RT-PCR). Altogether, this technology has promising clinical performances for the follow-up of patients with cancer

Lateral porous silicon interferometric transducer for on-chip flow-through sensing applications

International audienceMost porous silicon-based interferometric sensors targeting biosensing applications consist of vertical porous silicon layers created into a silicon wafer by electrochemical anodization and operate in a flow-over configuration. In this work, we present an alternative porous silicon interferometer based on porous silicon with horizontally oriented pores. This architecture permits the integration of flow-through porous silicon membranes within planar microfluidics. Fourier-transform infrared spectroscopy was used to obtain interference spectra from fabricated lateral porous silicon membranes and red shifts were observed upon filling microfluidic chips integrating the porous membranes with solvents of higher optical indices. This work proves that lateral porous silicon membranes are typical Fabry-Pérot interferometers with a sensitivity of more than 150 nm/RIU and a limit of detection less than 10−3 RIU, that is comparable to vertical porous silicon layers. Moreover, we have conducted simulation studies showing that the addition of Bragg mirrors on the membranes results in spectra with narrower fringes and lateral porous silicon interferometers with improved performances. After appropriate biofunctionalization of the porous silicon surface, lateral porous silicon membrane interferometers should offer alternative solutions for the development of porous silicon flow-through biosensors monolithically integrated on-chip

Transfer of III-nitride epitaxial layers onto pre-patterned silicon substrates for the simple fabrication of free-standing MEMS

International audienceIn recent years, the remarkable properties and potential applications of III-nitride (III-N) semiconductors have sparked a significant interest in the field of microelectromechanical systems (MEMS). Traditionally, III-N MEMS are fabricated through a process involving the epitaxial growth of III-N epilayers on a silicon substrate followed by etching the handle wafer to generate free-standing structures. In this study, we explore the potential of a relatively simple approach based on the two-dimensional (2D) material-based liftoff and transfer to fabricate III-N mechanical resonators. The methodology involves van der Waals epitaxy of III-N layers on 2D hexagonal-boron nitride (h-BN), which leverages the weak van der Waals adhesion between h-BN layers to lift off and transfer these layers from their original growth substrate to an alternative host substrate. The employed method is demonstrated by fabricating 600 nm thick GaN/AlGaN and 2.5 μm thick h-BN micro-resonators onto pre-patterned cavities etched in silicon substrates. These devices are characterized using laser Doppler vibrometry, enabling the observation of well-defined modes of vibration and resonant frequencies. Furthermore, finite element method simulations are performed to gain insights into the experimental observations and the mechanical properties of the transferred layers. This approach could be extended to transfer high-quality III-N MEMS devices onto various host substrates, including flexible substrates, and could be used to assess the mechanical properties of emerging III-N semiconductor materials

Crystallinity and piezoelectric properties of spray-coated films of P(VDF70-TrFE30): effect of film thickness and spin-crossover nanofillers

International audienceSpray coating the ferroelectric polymer P(VDF-TrFE) appears as an attractive approach for the fabrication of electromechanical transducers. However, it is important to elucidate how the crystallinity and associated piezoelectric properties depend on the coating thickness and additives. To this aim, we have spray-coated various substrates both with pure and nanocomposite films of the 70-30 % copolymer in a broad thickness range (200 nm – 30 µm). Using X-ray diffraction, differential scanning calorimetry, Raman spectroscopy and atomic force microscopy, we show that the obtained films are dense and homogeneous with ca. 50-60 % crystallinity, which consists of a majority polar β-phase, with slight alterations in the sub-micrometer thickness regime. Robust piezoelectricity and ferroelectricity are revealed at room temperature through both local hysteresis loops and lithography experiments using the piezoresponse force microscopy technique. After poling, the piezoelectric d33 coefficient displays values up to -19 and -11 pC/N for the pure copolymer and the composite, respectively. For a 33 vol% load of inorganic spin-crossover nanofiller, the switching properties are substantially improved and a coercive voltage <10 V is demonstrated for micrometric films. Overall, this approach appears as a promising way for the in-situ integration of high quality piezopolymer films into complex transducer geometries for sensing, actuating and energy harvesting purposes