Acoustical Streaming in Microfluidic CMUT Integrated Chip Controls the Biochemical Interaction Rate

Acoustical fluid mixing and streaming in microfluidic chips enhance the detection and fluid routeing capabilities in the lab-on-chip devices. Capacitive micromachined ultrasound transducers (CMUT) are easy to integrate into a closely packed environment, and they can be simultaneously used as integrated sensors and micropumps/mixers. In this paper, particular focus is given to examininge the impact of the acoustical fluid mixing to the kinetics of biochemical interaction. CMUT interdigital transducers for 10-MHz operation in water were designed and fabricated using the surface micromachining technique. Devices use Scholte type waves for biochemical detection and acoustical streaming. They also have the ability to control the directionality of acoustical streaming by +/-90° phase shift. The impact of acoustical streaming to the liquid diffusion kinetics in the microchannel and to the kinetics of adsorption of the bovine serum albumin (BSA) to the gold surface was investigated experimentally. For microfluidic experiments, CMUTs were assembled with 100 μm deep microchannels. It was determined that acoustical streaming can improve the diffusion rate through the microchannel. Also, it was shown that BSA adsorption rate can be controlled by changing the phase shift during excitation of the Sholte type waves.