Photoacoustic induced surface acoustic wave sensor for concurrent opto-mechanical microfluidic sensing of dyes and plasmonic nanoparticles

While there are a large number of reports on acoustic wave based sensors for evaluating mechanical parameters of fluid samples such as density, viscosity etc., devices for the simultaneous optical and mechanical characterization of fluids remain unexplored. In this context, effective utilization of surface acoustic wave (SAW) sensors comprising elliptically polarized evanescent waves for optical characterization of an analyte is intriguing. A combination of SAW and photoacoustic (PA) techniques presents promising capabilities for optical and mechanical characterization of fluids in micro volumes. We present a SAW-PA integrated device combining PA and SAW where the samples are introduced into a microfluidic channel. The PA signal generated from a sample in the microchannel of the SAW-PA device is mode-converted into SAW signals upon reaching the piezoelectric substrate, which is detected using the inter-digital transducer (IDT) deposited on the substrate. We further demonstrate the use of this SAW-PA compact platform for investigating the opto-acoustical properties of standard dye solutions and gold nanoparticles whose absorption is due to plasmonic resonance.