Surface acoustic wave concentration of microparticle and nanoparticle suspensions

A rapid particle concentration method in a sessile droplet has been developed using asymmetric surface acoustic wave (SAW) propagation on a substrate upon which the droplet is placed. The SAW device consisted of a 0.75-mm thick, 127.68 YXaxis-rotated cut LiNbO3 as a substrate. An interdigital transducer electrode (IDT) with 25 straight finger pairs in a simple repeating pattern, 12 mm aperture, and a wavelength of λ = 44 μm was patterned on the substrate. The IDT was then driven with a sinusoidal signal at the resonance frequency 8.611 MHz. To investigate the effect of particle type and size on the concentration process, several types of particles were used in this study, including fluorescent particles (1 μm), polystyrene microspheres (3, 6, 20, and 45 μm), and living yeast cells (1020 μm). Different RF powers were applied ranging from 120 to 510 mW. The concentration processes occurs within two to twenty seconds, depending on the particle size, type and input radio frequency (RF) power, much faster than currently available particle concentration mechanisms due to the large convective velocities achieved using the SAW device.