Ofer Manor, PhD, Chemical Engineering, Technion – Israel Institute of Technology, Haifa

There is a growing interest in deploying rapid diagnostic platforms at point of care (POC) facilities, such as decentralized clinics, and at domestic environments. However, conventional capillary-driven dynamic-wetting assays remain constrained by slow reaction kinetics, limited sensitivity for low-concentration analytes, and viscous drag when processing viscous physiological matrices such as saliva. To overcome these limitations, we present an experimental and theoretical study utilizing active surface acoustic wave (SAW) microfluidic actuation of mass transport within standard porous nitrocellulose membranes to enable rapid and high-sensitivity detection of salivary biomarkers associated with physiological conditions.

We employ a 20 MHz SAW transducer that leaks ultrasonic energy into a porous nitrocellulose membrane to drive pore-scale mass transport. To realize the physics, we developed an analytical framework that models the porous medium as an ensemble of small, identical cylindrical pores with varied orientations. By evaluating ultrasound induced mass transport through individual pores using the Navier-Stokes equations and spatially averaging the local flow across random pore orientation and membrane thickness, our model establishes that macroscopic transport scales with the ultrasonic power, closely matching experimental observations.

Experimentally, SAW-induced streaming achieves up to a 9-fold increase in advective velocity over passive capillary wicking for pure water and effectively overcomes the viscous resistance of saliva to flow. This enhanced mass transport promotes intra-membrane micro-mixing and intensifies colorimetric reaction kinetics, thereby enabling rapid color-change based detection even at low biomarker-molecule concentrations. Ultimately, this active acoustic platform provides a tunable, robust framework for enhanced POC diagnostic devices and establishes a generalizable protocol for accelerating arbitrary biomarker detection assays.