Detection of organics in aqueous solution using gold nanoparticles modified with mixed monolayers of 1-hexanethiol and 4-mercaptophenol

Gold nanoparticles functionalized with mixtures of 1-hexanethiol and 4-mercaptophenol were investigated as chemiresistor sensors for use in aqueous solutions. X-ray photoelectron spectroscopy (XPS) studies confirmed that it was possible to form mixed ligand compositions on the surface of the nanoparticles. Nanoparticle films with a higher proportion of 1-hexanethiol as the ligand resulted in higher impedances than those with lower proportions. The electrical response of the chemiresistor to toluene, dichloromethane, hexane and ethanol dissolved in water was found to depend strongly on the composition of the organic ligand used to cap the gold nanoparticles. 1-Hexanethiol-coated gold nanoparticles were sensitive to non-polar analytes whereas the sensitivity was reduced upon increasing the composition of 4-mercaptophenol on the surface. It was also shown that the sensitivity to ethanol could be enhanced 3-fold by using a sensor that was functionalized with a mixture of 60% 1-hexanethiol and 40% 4-mercaptophenol compared to a sensor functionalized with pure thiols only.