MEMS and Air-Microfluidic Solutions for Aerosol Monitoring

Aerosols are a suspension of solid or liquid particles in a gas (most commonly air). They affect occupational hygiene, human health, climate and many other aspects of our lives. Depending on their particle size and composition they exhibit different behavior and properties. MEMS and Air-Microfluidics platforms readily offer multidisciplinary tools, needed for aerosol manipulation and detection. In this thesis, we offer solutions for improving effective monitoring of the aerosols across different size ranges. First, we present new theory (extension of Bouguer-Beer-Lambert Law), designs, and experimental results of a novel opto-dielectrometric sensor that can, in real-time, measure the total incombustible content (TIC) of dust deposited in underground coal mines. TIC is the ratio between the incombustible content of deposited dust divided by total mass of all deposited dust and must be maintained below certain levels to reduce the risk of propagating an explosion in an underground mine. The sensor described in this thesis uses a combination of optical sensors and dielectrometric spectrometry to evaluate the TIC content of the continuously deposited dust-stack. The second part of this thesis presents the design, fabrication and experimental results for a novel air-microfluidic lab-on-a-chip sensor, which measures the mass concentration of the fine airborne particulate matter (PM). The sensor detects PM with the aerodynamic diameter (AD) of less than 2.5 $\mu$m (PM2.5) (fine PM) by measuring the deposited PM on a mass-sensing resonator. This novel sensor operates at flow-rates two orders of magnitude lower than the closest comparable devices. We also characterize the collection efficiency of the microfabricated virtual impactor (VI) by utilizing a novel opto-gravimetric investigation method. In addition, we present two effective methods for improving the functionality of the MEMS PM2.5 sensor by focusing the PM toward the sensing component region of the PM sensor. A novel microfabricated groove-induced envelope flow air-microfluidic PM focusing system (GRIP) is presented. In this system, horizontal focusing is achieved by enveloping the main flow using clean sheath flow from the sides of the microchannels. To extend the focusing to the vertical direction, grooved structures on top and bottom of microchannels are fabricated using a novel fabrication technique that is compatible with the DRIE fabrication process of other air-microfluidics PM sensors, making it easier to integrate these two components into small air-microfluidic circuits. In the optical version of this concentrator, a cylindrical confocal mirror cavity is designed to engineer the optical intensity profile needed to generate optical gradient force to propel the particles toward the center of the microchannels. Experimental results confirm the efficiency of these methods for focusing particles in air-microfluidic channels, enabling increased sensitivity and elimination of wall losses in future MEMS PM sensors.