Gold Nanoparticle Chemiresistor Sensors in Aqueous Solution: Comparison of Hydrophobic and Hydrophilic Nanoparticle Films

Chemiresistor sensors based on thin films of gold nanoparticles capped with hydrophobic hexanethiol or hydrophilic 6-hydroxyhexanethiol self-assembled monolayers are shown to respond to organic analytes in aqueous solution. Although considerable swelling of the 6-hydroxyhexanethiol-capped nanoparticle film by water occurred, the 6-hydroxyhexanethiol-capped nanoparticle film still responded toward the presence of organic analytes in aqueous solution. The response toward nonpolar analytes (toluene, hexane, dichloromethane) was reduced for the 6-hydroxyhexanethiol-capped chemiresistor compared to the hexanethiol-capped chemiresistor. However, for polar analytes such as ethanol the response sensitivity was reversed. A simple theoretical model describing the chemiresistor response in water is presented and was used to determine the partition coefficients between the nanoparticle film and water for ethanol and toluene.