Novel microfluidic lab-on-circuit for QCM-P oscillators

The Quartz Crystal Microbalance (QCM) has long been used for detecting chemical and biological materials in environmental samples. However, recent advancements to increase its sensitivity by adding micropillars (QCM-P) cause difficulty with existing circuit designs due to high dissipation and spurious secondary resonances. We address these issues in this work by designing a new circuit with a tuned tank circuit to stabilize oscillation frequency, automated gain control (AGC) to compensate for high dissipation, and a digital amplifier and counter circuit to automate computer interfacing. We verify the contributions by testing the circuit with both QCMs and QCM-Ps in air, water, and viscous test samples, as well as a side by side comparison of the circuit with and without the tank circuit. We achieve stable oscillation under widely varying dissipation levels and demonstrate that the circuit successfully drives and measures the resonant frequency of a QCM-P in a proof of concept biomolecular adsorption test to determine mass loading sensitivity. We achieve 5x increase in frequency shift from the same mass loading compared to QCM with minimal noise increase. We conclude that our circuit enables future work towards extremely high sensitivity environmental sensors that are able to measure samples with widely varying viscosities.