INTEGRATED MICROSYSTEM TECHNOLOGIES FOR CONTINUOUS PERSONAL MONITORING OF AIRBORNE POLLUTANT EXPOSURES

ABSTRACTINTEGRATED MICROSYSTEM TECHNOLOGIES FOR CONTINUOUS PERSONAL MONITORING OF AIRBORNE POLLUTANT EXPOSURESBy Heyu Yin Exposure to airborne pollutants, including gaseous toxins and particulate matter (PM), threaten human health and are of growing world concern. Unfortunately, the specific mechanisms behind medical conditions induced by air pollutants, as well as the socioeconomic demographics that underpin these conditions, are poorly understood. This is due, in large part, to a lack of accurate data detailing exposure profiles of individuals who suffer from acute and chronic health conditions. Air pollution levels and the activities of individuals exhibit a large degree of spatial and temporal variation, which both challenge the assessment of personal exposures. Moreover, health impacts vary significantly with chemical composition and particle size of pollutants, which further complicates effective monitoring. Utilizing a combination of microfabrication, microfluidics and electrochemical sensing technologies, this thesis research explored a microsystem solution to these challenges that can achieve high spatial resolution by providing a compact, mobile/wearable monitoring device and can achieve high temporal resolution by enabling continuous collection of personal exposure data. To create a compact monitor for multiple gaseous air pollutants, unique microfabrication procedures and electrochemical techniques were established, enabling a gas sensor array that features room temperature ionic liquid electrolyte and achieves high reliability and repeatability. In addition, a novel PM monitoring platform that uniquely employs microfluidics to achieve real-time continuous measurement was introduced, and key component technologies were developed. First, to measure PM concentrations within a compact microfluidic device, an electrochemical quantification method based on the ionic electret effect was employed for the first time using microfabricated planar electrodes and a microelectronic instrumentation module. Second, to permit real-time analysis of PM across a wide range of particle diameters, multiple generations of a microfluidic size fractionation component were developed. The first microfabricated size fractionation device realized the deterministic lateral displacement (DLD) method with a critical diameter of 2.5 μm and was successfully demonstrated to separate 10 μm and 1 μm particles with around 100% efficiency. The next size fractionation design aimed to provide multi-size separation over a wide dynamic range (~1000) of particle sizes that impact human health, down to ultrafine (nanoscale) PM. The resulting externally balanced cascade DLD concept was implemented within a mathematic model that predicts size fractionation of PM, from 10 μm to 0.01 μm, can be achieved with a minimum total device length of ~41mm using a four-section cascade. Finally, to further miniaturize the size separation device toward a monolithic implementation, an internally balanced cascade DLD design concept that can omit extra inputs and outputs was introduced and thoroughly analyzed using computational fluid dynamics simulations. The combined results of this research overcome many challenges that currently impede the desperately needed realization of personal airborne pollutant monitors offering wearable, real-time and continuous operation for unprecedented spatial and temporal resolution.