Micromachined devices for an airborne bio-particle analysis system

Citation

Desai, Amish S. (2000) Micromachined devices for an airborne bio-particle analysis system. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ge1w-t045. https://resolver.caltech.edu/CaltechTHESIS:10012010-095709235

Abstract

The goal of this thesis is to develop micromachined devices for an automated miniaturized airborne bio-particle analysis system. The realization of such a system is complex requiring a particle capture, transport, collection, sample preparation, and analysis. Accordingly, microelectromechanical systems (MEMS) teams have studied and developed micro-pumps, valves, channels as building blocks for a miniature chemical analysis system. In this thesis, novel micromachined solutions to some of these tasks are presented. Specifically, the development of: 1) a low voltage, air-based electrostatic particle transportation system, 2) an air-to-liquid interface design for transport of airborne particles into a liquid environment 3) a micro-chip electrospray (ES) mass spectrometer interface for small volume(nL) mass spectrometry, 4) and fast mixers (<100μs) for the study of chemical reaction kinetics. The particle transport system consists of 3-phase electrode arrays covered by photoresist and Teflon. Extensive testing of this system has been done using a variety of insulation materials, thicknesses (0-12μm), particle sizes (1-10μm), particle materials (metal, glass, polystyrene, spores, etc.), waveforms, frequencies, and voltages. Although previous literature claimed it impractical to electrostatically transport particles with sizes of 5-10μm due to complex surface forces, this effort actually demonstrates 90% transportation efficiencies with the optimal combination of insulation thickness, electrode geometry, and insulation material. As the second step, this particle transportation technology has also been integrated with an active micromachined filter and an air-to-liquid silicone rubber interface. Two methods of air to liquid particle transport were explored — moving particles across a stationary fluid meniscus and the other, moving meniscus across stationary particles. Third, the development of a micron-sized MEMS nozzle (1-3 μm orifice diameters) is presented with successful demonstration of its application for electrospray ionization mass spectroscopy. MEMS scaling issues were verified with the flow visualization of the Taylor Cone on this nozzle. Fourth, a 1 cm x 1 cm x 1 mm DRIE silicon mixer capable of initiating and quenching (starting and stopping) chemical reactions in intervals as short as 100 μs was characterized by employing two carefully chosen chemical reactions with reaction time constants of 3 ms and 9 ms along with visualization techniques using dyes and acid-base indicators.

Thesis Files