Sensitivity, Selectivity, and Nanodimensional Effects in Gold Nanocluster Vapor Sensors

A chemiresistor vapor sensor based on electron transport through an ensemble of ligand-stabilized gold nanoclusters is made exceptionally sensitive and selective by terminal carboxylic acid functionalization of the alkanethiol ligand. The directionality of the response (conductance increase or decrease) is strongly dependent on the nanoscale dimensions of the gold core and ligand shell thickness. Films of gold nanoclusters composed of a 2-nm metal core with a 0.5-nm S(CH₂)₅COOH shell are compared with those based on an 8-nm core and a 1.5-nm S(CH₂)₁₅ COOH shell. Sensitivity toward amine vapors covered spanned 4-5 orders of magnitude with a detection limit lower than 0.1 ppm and respective selectivity factors of 100× and 20× over interferent vapors. Sensor isotherm measurements on a series of trialkylamine vapors displayed a sensitivity dependence that correlates with vapor pressure. Comparative responses to deuterated and nondeuterated triethylamine vapor exposures were identical and ruled out a sensor transduction mechanism that couples analyte vibrational modes with electron tunneling between gold nanocluster cores.