Ambient particle sensing with single entity electrochemistry: methods and applications

Air pollution from diverse sources became a topic of growing public attention and media coverage ranging from air quality forecasts to effects on human health. Poor air quality is estimated to be responsible for more than 9 million early deaths each year and is being exacerbated by the increasing severity of climate events. Among various air pollutants, airborne particulate matter (PM) monitoring scenarios for medical diagnostics, environmental surveillance, industrial safety, agriculture, energy, military and space applications demand new sensing methods and capabilities. PM monitoring is very challenging due to the heterogeneity of PM, i.e. they can vary in size, concentration and composition depending on emission sources and processes undergone. Single-entity electrochemistry (SEE) was demonstrated for direct electrochemical detection and counting of various nanoparticles, especially redox-active metals. In this approach, particles are suspended in a solution as a colloidal or suspension. Particles as small as nanometers can be detected by measuring the current signal change upon particle collision with an ultra-microelectrode (UME). The magnitude and/or duration of the response signal (e.g. current) can be a function of the particle’s size and chemical components as well as the electrode’s material and bias potential. In this presentation, we will present methods using SEE for direct electrochemical detection and counting of nanoparticles, especially non-metals particles (e.g., carbon and crystalline silica) with high sensitivity and specificity. Carbon and silica PM are abundant in the mining industry and exposure to respirable particles is hazardous for the safety and health of workers who work in surface and underground mining. We will also show the design, fabrication, and development of the integrated PM sensor device that incorporates SEE methods for the real-time quantitative detection of PM in concentration, size and chemical types.