An ultrasonic micromachined integrated capacitive sensor for biological sample preparation on a microfluidic platform

In this paper, we report on a capacitive sensor for particle detection and characterization integrated with an ultrasonic microfluidic actuator. We have previously reported on an acoustic vortex generator for particle trapping. Particles get trapped inside fluid vortices near the edges of surface micro-machined polysilicon disk structures inside the channel. By integrating coaxial cable interconnects underneath the polysilicon disk, a capacitor is formed between the electrode and the vibrating poly-disk. When two such capacitors are connected in a bridge circuit, we can measure the differential output to detect very small changes in capacitance. Such a change could be because of (a) unequal bending of the disk over two electrodes - this helps us capacitively measure the mode of vibration or (b) change of dielectric constant because of presence of beads/biological species - this helps us detect presence of particles precisely.