Synthesis and Characterization of Monolayer-Protected Gold Nanoparticles and Their Organoplatinum Composites as Vapor-Sensitive Microsensor Interface Materials

Michael P. Rowe, PhD,
Environmental Health Sciences, School of Public Health,
University of Michigan

ABSTRACT: Organothiolate-monolayer-protected gold nanoparticles (MPNs) offer numerous advantages as vapor-sensitive interface materials in microfabricated chemiresistor (CR) arrays. Small quantities of gas-phase species partitioning into thin MPN-sensor films cause large changes in film resistance. In this series of studies, the synthesis, characterization, and testing of MPNs, alone and as composites with various organoplatinum charge-transfer complexes, are explored. A new single-phase MPN synthesis, which retains the advantages of existing methods, is described that avoids ionic contamination from the phase-transfer catalyst (PTC) used in the conventional dual-phase synthesis. Residual PTC leads to a frequency-dependent current through the MPN film, long stabilization times, and anomalous vapor responses. MPN and PtCl2(olelfin)(pyridine) composite films were shown to selectively interact with olefin vapors. The unique decrease in the CR film resistance is attributed to a reversible Pt-olefin charge-transfer interaction. Structurally analogous non-olefins invariably cause an increase in the CR film resistance. Selective measurement of several olefins and reductions in their detection limits by as much as 104-fold are achieved by use of these composite CR interface films. In a follow-on study, composite films of MPNs with PtCl2(pyridine)2 were shown to reversibly and selectively interact with pyridine vapor and environmental tobacco smoke marker vapors. Although the degree of selectivity is less than that observed with the olefins, the results support the use of organometallic additives in MPN films as a general means of selectively enhancing sensor performance.
BIO: Michael Rowe received a BA in chemistry with honors from Knox College in June of 2000. As an undergraduate student, he designed and synthesized reduced-symmetry copper(II) tetrakis (carboxylate) liquid crystals, with Dr. Thomas Clayton, from December 1997 to 2000. In 2003, he received a Masters in Chemistry from the University of Michigan and began working with Dr. Edward T. Zellers. Recently, Michael successfully defended his dissertation research. His thesis was on the synthesis of thiolate-monolayer-protected gold nanoparticles and the application of these materials as the vapor-sensitive layer of chemiresistor sensors. In this work, a new single-phase synthesis of gold nanoparticles was developed, and the implications of ionic contamination on sensor performance were illustrated. Additionally, composite films of nanoparticles and organoplatinum complexes were used to produce sensors with unique selectivity for gas-phase olefins, and for environmental tobacco smoke marker vapors. After earning his Ph.D. in materials chemistry, he will be continuing to work with Dr. Zellers on nanoparticles for the WIMS micro-GC chemiresistor sensor array.