Optical knife-edge detection for micropillar-based microfluidic viscometer

Abstract

We demonstrate the use of an optical knife-edge technique in micropillar-based microfluidic chips, which are intended for viscosity measurements. Our demonstrations rely on the use of a single photodiode, offering a significant cost, form factor and computational efficiency advantage over CMOS camera detection. Our readout methodology involves the utilization of pillars as waveguides, such that a laser is coupled from the backside of the fluidic chip, while the output light is monitored with a photodiode using knife-edge detection. The bending of the pillars due to applied flow alters the observed light intensity, from which the bending angle could be deduced. We present ray-tracing simulations and conduct proof-of-concept experiments on a micropillar-based microfluidic chip. The bending of the pillar observed with the knife-edge technique matches well with that observed with a camera. With further development, the proposed methodology can be employed as a compact and low-cost point-of-care instrument for real-time viscosity measurements.