Focusing of Airborne Particles Using Groove-Induced Envelope (GRIP) Flow Air-Microfluidic Concentrator

Monitoring personal exposure to airborne particulate matter (PM) necessitates the need for ubiquitous portable PM sensing systems. Most current microfluidic PM detectors will be significantly improved if the particles suspended in the air-stream are focused into a narrow stream. In this paper, we present a novel microfabricated groove-induced envelope flow (GRIP) air-microfluidic PM focusing system. In this device, the horizontal focusing is achieved by enveloping the main flow using clean sheath flow from the sides of the microchannels, while vertical focusing is achieved using grooved structures on top and bottom of the microchannels. The grooves 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. The performance of this system was evaluated using the opto-gravimetric method. Mono-dispersed polystyrene latex spheres were injected into the GRIP system and subsequently collected on membrane filters attached to the outlet. Epi-fluorescent microscopy was then used to image the distribution of the particles on the filter. The experimental results confirm that the efficiency of the GRIP device for focusing particles in air-microfluidic channels, enabling increased sensitivity and elimination of wall losses in future micro-electro-mechanical-systems PM sensor.