Mono layer-Capped Cubic Platinum Nanoparticles for Sensing Nonpolar Analytes in Highly Humid Atmospheres

We report on the feasibility of cubic Pt nanoparticles (NPs) capped with four representative organic ligands, viz. oleylamine (ODA), 11-mercaptoundecanol, 11-mercaptoundecanoic acid, and benzylmercaptan, for sensing gaseous nonpolar analytes in humid atmospheres. Chemiresistors based on cubic Pt NPs with nonpolar ligands show a very large increase in resistance upon exposure to nonpolar analyte vapors, combined with a low sensitivity to polar analyte vapors, especially to water. The sensing mechanism can be understood in terms of analyte-induced changes in the NP-NP core distance and changes in the permittivity of the medium between the NPs. The sensing capabilities of the Pt NP chemiresistors for nonpolar molecules in highly humid atmospheres are demonstrated by dosing an ODA-capped cubic Pt NP sensor with air mixtures containing low octane concentrations and high humidity levels that are typical for many applications. The simple construction, low cost, stability, fast response, and high sensitivity to nonpolar molecules, together with the low sensitivity to water vapor, are promising features for sensing applications in real confounding atmospheres.