Surface-acoustic-wave biosensors and microfluidics
Surface acoustic waves (SAWs) are acoustic waves that travel along the surface of an elastic material, with an amplitude that typically decays exponentially with depth into the substrate. Given their very superficial nature, SAWs are highly sensitive to surface perturbations of the substrate along which they propagate. For example, they can interact with liquid droplets or streams inducing macroscopic fluid manipulations or, in a different configuration, be exploited for sensing applications. The interest of the NeuroSens group in this field is to explore and study novel SAW-driven microfluidic phenomena, and apply this new knowledge to the fields of biosensing and cell biology.
Ultra-high-frequency Love surface acoustic wave device for real-time sensing applications
Love surface acoustic wave (L-SAW) devices are ideal for real-time sensing applications. High miniaturization and sensitivity are desirable in particular for point of care diagnostics or on-site measurements. It is possible to enhance both these parameters by increasing the working frequency of these devices, but this is still a challenge. Indeed, the ultra-high frequency (UHF) range has not been explored yet for L-SAW sensing devices because it requires non-trivial fabrication and measurement setup. Here, we present a multiplexable, highly miniaturized UHF L-SAW device for real-time sensing applications. The sensor performance was first tested with mixtures of different volume percentages of isopropyl alcohol (IPA) in water. Measurements of phase and amplitude (related to change of density and viscosity, respectively) show higher sensitivity and dynamic range than a representative 100 MHz L-SAW sensor. Then, we measured the adsorption kinetics of three different concentrations of bovine serum albumin (BSA) in water on the sensor surface, demonstrating biomolecule detection. The all-electrical readout system as long as the small dimensions make the presented device particularly promising for portable UHF sensing platforms. Nonetheless, the higher sensitivity and dynamic range obtained with respect to a representative 100 MHz L-SAW sensor as long as the real-time measurements of the BSA adsorption (with an estimated limit of detection of 90 ng/mm2) show that UHF Love SAW sensors have the potential to be used for bio-sensing applications, such as point of care diagnostics.
Full-SAW Microfluidics-Based Lab-on-a-Chip for Biosensing
Many approaches to diagnostic testing remain decades old. Well-established biosensing technologies (e.g., enzyme linked immunosorbent assays, radio-immunoassays) typically cannot fulfill the requirements of portability and ease of use necessary for point-of-care purposes. Several alternatives have been proposed (e.g., quartz-crystal-microbalances, electrochemical sensors, cantilevers, surface-plasmon-resonance sensors) but often lack high performance or still necessitate bulk ancillary instruments to operate. Here we present a highly sensitive, versatile and easily integrable microfluidic lab-on-a-chip (LoC) for biosensing, fully based on surface acoustic waves (SAWs). By using ultra-high-frequency resonator-biosensors, we show that it is possible to perform highly sensitive assays in complex media. This all-electrical readout platform is benchmarked with the biotin-streptavidin binding in presence of non-specific binding proteins (serum albumin) at physiological concentration. The benchmark experiments were performed with the idea of mimicking a biological fluid, in which other molecular species at high concentration are present together with the analytes. We demonstrate that this LoC can detect sub-nanomolar concentrations of analytes in complex media. As a comparison with similar acoustic-wave based systems, this full-SAW platform outperforms the standard commercial gravimetric sensors (i.e., quartz-crystal-microbalances) and the more common Love-SAW biosensors. This full-SAW LoC could be further developed for the detection of biomarkers in biological fluids.