William H. Steinecker

An Integrated Micro-Analytical System for Complex Vapor Mixtures

A micro gas chromatograph (muGC) capable of quantitatively analyzing the components of complex vapor mixtures at trace concentrations is described. The muGC features a micro- preconcentrator/focuser (muPCF), dual-column pressure- and temperature-programmed separation module, and an integrated array of nanoparticle-coated chemiresistors. The latest design modifications and performance data are presented. Highlights include a 4-min separation of a 30-component mixture with a 3-m DRIE Si/glass microcolumn, a 14-sec separation of an 11-component mixture on a 25-cm microcolumn, a complete multi-vapor analysis from a hybrid microsystem that combines analytical, rf- wireless, and microcontroller modules, and a rapid analysis driven by a 4-stage peristaltic micropump.

A Micropump-Driven High-Speed MEMS Gas Chromatography System

We report (1) the integration of the first functioning MEMS gas chromatography system ( muGC) featuring a micropump, a micro-column, and a micro-chemiresistor sensor array; and (2) experimental demonstration of the state-of-the-art multi-vapor gas separation and detection. In particular, we report the best GC analysis data from the first micropump-driven muGC system to date: the separation and detection of 11 volatile organic compounds (VOC)s within only 78 seconds while consuming only 15.1 mW of power within a small volume of 0.5 cc. We also report the use of temperature programming (TP) of the separation column for fast analysis, which shortened the analysis time from 78 seconds to 24 seconds while maintaining gas analysis resolution.

Electron-Beam Patterned Monolayer-Protected Gold Nanoparticle Interface Layers on a Chemiresistor Vapor Sensor Array

Use of electron-beam induced crosslinking (EBIX) to pattern films of thiolate-monolayer-protected gold-nanoparticles (MPNs) on chemiresistor (CR) vapor sensors is described. MPNs with alkyl, cyanoalkyl, phenoxyalkyl, and hydroxyfluoroalkyl thiolate tail groups were patterned on integrated arrays of interdigital electrodes using electron doses of 500-750 μC/cm2. The dc resistances of solvent cast films of these MPNs decrease and the baseline-normalized changes in resistance to each of five organic vapors increase to different degrees with increasing electron-beam dose. Relative responses patterns from an array of MPN-coated CR sensors for the test vapors change after EBIX patterning and the diversity of responses is diminished, on average, but it is still projected to be sufficient for the discrimination of most of the individual test vapors and binary mixtures. Results are rationalized in terms of expected changes in ligand structures and film properties following EBIX patterning using known models of electronic conduction, and vapor-induced changes of conduction, through MPN films. The implications of the results for creating arrays of densely packed MPN-coated CRs as detectors for microanalytical systems are considered.

Chemiresistor array with nanocluster interfaces as a micro-GC detector

An integrated array of chemiresistor (CR) microsensors employing a novel set of Au-thiolate monolayer-protected nanoclusters (MPN) as interface materials has been developed and tested as an ultra-low-dead-volume detector for a micro gas chromatograph (/spl mu/GC). Six MPNs 3-5 nm in mean core diameter each with a different type of organo-thiolate ligand were synthesized by a single-phase method, spray cast onto interdigital electrodes, and exposed to several organic vapors. Four of these MPNs were coated onto the same CR array and used as a detector for a conventional GC to analyze a mixture of 15 vapors. The array provides characteristic vapor response patterns, linear calibration curves, and good overall sensitivity, which increases at lower temperatures and detector-cell flow rates. On the basis of injected mass, GC responses indicate that detection limits in the low part-per-trillion range are achievable from preconcentrated sample volumes of <1 L. Sensitivity does not vary significantly among similarly coated CRs having electrode spacings ranging from 0.1-15 /spl mu/m consistent with a response model based on bulk-film swelling.

Microscale Gas Chromatography with Microsensor Array Detection: Challenges and Prospects

The capability to analyze complex mixtures of airborne volatile organic compounds (VOCs) at low concentrations; in situ; has implications for environmental monitoring; worker exposure assessment; biomedical diagnostics; and population security. Since standalone microsensor arrays lack this capability; upstream separation of mixture components; often preceded by preconcentration; is required. Although significant advances have been made via MEMS technologies in the development of microscale gas chromatographic (μGC) systems; many challenges remain. This presentation will review selected aspects of the state-of-the-art in μGC for VOC mixture analysis. Here; we emphasize our progress toward a wearable μGC prototype.