DC pulse-powered microdischarges on planar electrodes and their use in vapor and liquid phase chemical sensing in ambient air.

摘要

This report explores DC pulse-powered planar microdischarges between planar metal electrodes that are located on glass substrates and their possible use in handheld chemical sensing systems.; For electrode separations >200mum discharges, between two electrodes take the form of a pulsed arc, providing broadband optical emission and select peaks from chemical species present in the glow. The separate temporal characteristics of the line and background spectra present opportunities to improve detection. This concept is evaluated by isopropanol vapors (100ppm) using emission from CH fragments.; For electrode gaps of 75mum, the discharge characteristics are intermediate between arc and glow discharges. These hybrid discharges can be tuned to have the required glow or are-like characteristics. They have low broadband emission, greater longevity, and consume less power than the pulsed arc discharges. They can detect 17ppm of acetone without pre-concentration in air ambient.; The energy of the microdischarges can be controlled by using a three-electrode (flashFET) scheme, which uses separate electrodes for initiation and powering of the discharge. A strategically located high impedance gate electrode permits the use of pulses 100V between the source and drain. It consumes 22.5muJ/discharge.; Microdischarges employing doped liquid cathodes are used as tunable optical sources to fluoresce biochemicals in microfluidic systems. A stacked microchip that integrates a microfluidic wavelength-tunable optical source, a biochemical sample reservoir and optical filters is used to realize the system. For DNA fluorescence, a BaCl2 solution is used as cathode, to emit light at 454nm and 493nm. For tryptophan fluorescence, the cathode contains Pb(NO3)2 solution to provide 280nm emission.; A liquid discharge microchip, which uses a wetted porous cathode, is developed for analysis of water samples. It has an electrode gap of 50mum, an active area of 1x1mm2 and can detect 2ppm of aqueous Cr. Finally, a handheld system based on this technology is developed. It uses a module with swappable gas and liquid discharge chips and battery-operated circuit, and a commercially available spectrometer and electronic interface.; Together these results address many of the key challenges in realizing discharge based chemical sensors and demonstrate their feasibility in handheld systems operating in ambient air.