Micro fl uidic Electrochemical Sensor for On - Line Monitoring of 2 Aerosol Oxidative Activity

8 ABSTRACT: Particulate matter (PM) air pollution has a 9 significant impact on human morbidity and mortality; 10 however, the mechanisms of PM-induced toxicity are poorly 11 defined. A leading hypothesis states that airborne PM induces 12 harm by generating reactive oxygen species in and around 13 human tissues, leading to oxidative stress. We report here a 14 system employing a microfluidic electrochemical sensor 15 coupled directly to a particle-into-liquid sampler (PILS) 16 system to measure aerosol oxidative activity in an on-line 17 format. The oxidative activity measurement is based on the 18 dithiothreitol (DTT) assay, where, after being oxidized by PM, the remaining reduced DTT is analyzed by the microfluidic 19 sensor. The sensor consists of an array of working, reference, and auxiliary electrodes fabricated in a poly(dimethylsiloxane)20 based microfluidic device. Cobalt(II) phthalocyanine-modified carbon paste was used as the working electrode material, allowing 21 selective detection of reduced DTT. The electrochemical sensor was validated off-line against the traditional DTT assay using 22 filter samples taken from urban environments and biomass burning events. After off-line characterization, the sensor was coupled 23 to a PILS to enable on-line sampling/analysis of aerosol oxidative activity. Urban dust and industrial incinerator ash samples were 24 aerosolized in an aerosol chamber and analyzed for their oxidative activity. The on-line sensor reported DTT consumption rates 25 (oxidative activity) in good correlation with aerosol concentration (R from 0.86 to 0.97) with a time resolution of approximately 26 3 min.