Chemiresistor coatings from Pt- and Au-nanoparticle/nonanedithiol films: sensitivity to gases and solvent vapors

Chemiresistor coatings are fabricated via layer-by-layer self-assembly using 1,9-nonaneditbiol (NT) and dodecylamine-stabilized Pt- or Au-nanoparticles. The film thickness, as determined by atomic force microscopy (AFM), is 66 +/- 2 and 31 +/- 1 nm, respectively. These film materials show linear current-voltage characteristics and conductivities in the range of similar to10(-3) and similar to10(-4) Omega(-1) cm(-1) at room temperature. The sensitivity of the films is investigated by dosing them with the gases ammonia (NH3) carbon monoxide (CO) and vapors of water and toluene in the concentration range from 300 ppb to 5000 ppm. To all analytes the films respond with an increase of their resistance. Although the total signal intensities are rather weak, these sensors show a very high signal-to-noise ratio, which enables a detection limit for NH3 below 100 ppb. The response dynamics and the curvature of the response isotherms indicate that NH3 and CO bind significantly stronger to the film material than water or toluene. This result is interpreted with the assumption that NH3 and CO bind to vacant sites on the metal nanoparticle cores, whereas water and toluene interact preferably with the NT linker molecules. (C) 2003 Elsevier B.V. All rights reserved.