Real time size-dependent particle segregation and quantitative detection in a surface acoustic wave-photoacoustic integrated microfluidic system

Abstract

We present an integrated microfluidic system capable of size-dependent separation, concentration, and quantitative detection of microparticles on a single piezoelectric (128° YX LiNbO3) substrate using surface acoustic wave (SAW) and photoacoustic (PA) technique. First, using a tilted-angle standing SAW highly efficient segregation of polystyrene beads of two different sizes was achieved in a continuous particle flow inside the channel. Flow-assisted migration of separated particles would then undergo particle aggregation using a SAW device, to preconcentrate the sample before detection The optical absorption of the pulsed laser by the polystyrene microparticles generates the PA wave. The detection scheme involves sensing the SAW generated by the optically induced mechanical resonance of the PA-wave inside the microfluidic channel. The SAW-PA signal was further correlated to the particle count. The developed integrated microfluidic system performs effectively, with separation efficiency above 95% for the 3- and 10-μm diameter polystyrene beads. The separated 10-μm particles were directed into the sensing chamber, where a SAW device concentrate the particles before real-time quantitative detection. The configuration and theoretical aspects of each integrated segments were studied and explained. The sensor presented a reliable (R2=0.98) detection of the 10-μm particles down to 7 particles in 10μL of the sample volume in 15min. This technique paves the way to the design and development of future lab-on-a-chip (LOC) devices for clinical analyte detection and quantification.