Size-fractionated electrochemical quantification for compact monitoring of fine particulate matter

Abstract

Airborne particulate matter (PM), especially fine particles with a diameter smaller than 2.5 µm (PM2.5 classification) are a deadly air quality concern. One possible solution to reduce individual exposure to fine PM is to develop a low-cost and wearable PM monitor. This paper introduces a new approach for continuous quantification of particles that expresses a resolution suitable for fine PM measurement and a capacity for miniaturization to support wearable monitoring using a unique combination of particle size fractionation and electrochemical quantification. High efficiency size fractionation is performed through a microfluidic device utilizing an I-shape pillar based deterministic lateral displacement (DLD) method to provide particles of uniform size for downstream quantification. Measurement of PM concentration was explored using different electrochemical methods and electrode materials, and differential pulse voltammetry (DPV) with gold electrodes was found to give the best sensitivity and repeatability. Our results show that the mechanism responsible for the particle’s electrochemical response is the ionic electret effect, linking this effect to PM measurement for the first time. A compact electrochemical instrumentation system was implemented to demonstrate this detection scheme as a wearable PM monitoring platform. DPV results with polystyrene particles demonstrate a sensitivity of for 1 µm particles of 3 aA/particle. Both size fractionation and quantification results show that this platform is a promising option for portable fine PM monitoring.