Capacitive detection of micrometric airborne particulate matter for solid-state personal air quality monitors

A novel microsensor for capacitive detection of particulate matter (PM) directly in air is presented. The feasibility of detecting single PM10 particles (calibrated 10 μm polystyrene beads) by means of ad-hoc designed coplanar microelectrodes (4 μm gap), a PDMS air deposition system, and a low-noise (∼2 aF capacitive resolution) readout electronics is experimentally demonstrated. Finite element numerical simulations have been performed to optimize the design of the microelectrodes, investigate the detection limit and validate the experimental results. The real-time deposition on the sensor surface of sequences of single industrial talc particles (average diameter of ∼8 μm, corresponding to a signal of ∼12 aF) has been successfully tracked with 10 ms temporal resolution and, subsequently, validated by microscope inspection. This CMOS- and MEMS-compatible capacitance detection technique enables radical miniaturization of next generation air quality monitors, paving the ways to their embedment in personal portable devices for pervasive mapping of air pollution.