Development of a microfluidic device with integrated high frequency ultrasound probe for particle characterization

A microfluidic flow device incorporating a 200 MHz ultrasound probe has been developed to rapidly characterize micron-sized particles. The device hydrodynamically focuses a particle stream under the ultrasound transducer, where pulse-echo ultrasound is used to probe the passing particles one by one. When the ultrasound wavelength is similar to the particle size, the scattered wave depends strongly on the particle size, and the sound speed and density of the particle and surrounding fluid. Each particle type and size has a unique acoustic signature from which it can be identified. To demonstrate this, polystyrene microbeads with two different sizes were used, 6 or 10 μm. Each particle produced an ultrasound signal, and it was identified as either 6 or 10 μm according to unique features in the ultrasound power spectrum. The ultrasound spectral features agreed with those measured from stationary beads using an acoustic microscope, and also to theoretical predictions. These results show for the first time, a new high-speed method of characterizing micron-sized particles using sound waves with applications towards classifying biological cells.