Gold-nanoparticle/dithiol films as chemical sensors and first steps toward their integration on chip

Networked films comprised of Au-nanoparticles and organic dithiols were deposited onto silicon or glass substrates via repetitive self-assembly from solution. The substrates were equipped with interdigitated electrode structures for electrically addressing the films. Dodecylamine stabilized Au-nanoparticles with a core diameter of 4 (+/-0.8) nm were used for film assembly. The metal cores were networked through 1,n-alkylenedithiols with chain lengths varying from 6 to 20 methylene units. With increasing number of methylene units, the conductivity of the films decreased by several orders of magnitude without following a monoexponential decay. When dosing the films with organic vapors (toluene, 1-propanol, 4-methyl-2-pentanone) their resistance increased reversibly. The amplitudes of this response increased strongly with increasing length of the linker molecules. In contrast, the sensitivity to water vapor was marginal for all alkylenedithiol-linked films. However, insertion of polar amide groups into the backbone of the linker decreased the sensitivity to toluene and significantly enhanced the sensitivity to water. The deposition of sensor films on chip from organic solvents could be directed by using a patterned CaO mask. After film deposition, the lift-off of nanoparticles from protected parts of the substrate was achieved by dissolving the mask in aqueous solution at ambient temperature.