Waveguide micro-opto-electro-mechanical resonant chemical sensors.

We demonstrate a silicon micro-opto-electro-mechanical sensor based on mass-loading of a chemo-selective polymer coated onto a microbridge. The sensor is probed optically using an on-chip waveguide Fabry-Pérot interferometer for high resolution displacement and resonant frequency measurement. The mechanical resonator is designed with paddles to simplify chemo-selective polymer deposition and to minimize any strain effects from the polymer during analyte sorption. Water vapor sensing experiments indicate mass-loading with minimum humidity detection of DeltaRH = 0.25% corresponding to a measured limit-of-detection of 68 parts-per-million. The sensor response time constant is 30 s with minimum frequency noise of 58 Hz at 149.4 kHz resonance. The measured mass-loading resolution is 4.6 picograms. We extract the chemo-selective polymer's partition coefficient and confirm that strong sorption and mass-loading occurs. Various device improvements are discussed, including scaling up to large single-chip sensor arrays, increasing mass-loading resolution by adjusting the device geometry, and using other chemo-selective polymers with larger partition coefficients. These improvements suggest parts-per-billion limit-of-detection levels for a variety of toxic chemicals.