A 24.4μW Room Temperature Gas Sensor Based on Molecularly Imprinted Polymers Demonstrating SARS-Cov-2 and D-Glucose Aerosol Sensing

Small and battery-powered gas sensors offer the ability to detect airborne viruses, environmental pollutants, or health data for next-generation public health and safety applications through low-cost, distributed monitoring. Unfortunately, conventional gas sensors require heating to temperatures often greater than 100°C, which requires significant power consumption (e.g., 25mW in [1]) and cannot be rapidly duty-cycled due to long thermal-time constants. To eliminate the need for heating, other prior work utilizes techniques such as gas-selective polymer films that change the frequency of RF MEMS resonators [2]; the 2.5GHz operation in [2], however, required readout circuits that consume ~1mW, which is still too high for applications that demand extreme system and battery miniaturization. Recent work has shown that Molecularly Imprinted Polymer (MIP)-based gas sensors, which are functionalized based on the shape of the target molecule, offer extremely attractive sensitivities (parts per billion) by measuring minute changes (e.g., ΔR≈10mΩ in [3]) in the polymer resistance
$(\mathrm{R}_{\text{base}}\approx 10-1000\Omega)$
with no heating or high frequencies required. Unfortunately, most prior-art resistance-to-digital converters (RDCs) have difficulty achieving the required high-resolution for such small base resistances at low power, making them incompatible with MIP gas sensors. For example, a direct readout stage cannot easily achieve the necessary resolution in a single stage [4], autoranging can achieve high dynamic range at the cost of poor linearity at the range junctions [5], or feedback can be used to linearize a VCO-based ADC readout [6] that would, unfortunately, require high-power feedback DACs to operate with a low-resistance MIP sensor (Fig. 1 top left).