Vapor sensitivity of networked gold nanoparticle chemiresistors: Importance of flexibility and resistivity of the interlinkage

In this study we investigated the response behavior of chemiresistors made from differently interlinked networks of gold nanoparticles. Our results show that the degree of flexibility and conductivity of the interlinkage between the nanoparticles has a profound impact on the response characteristics of such sensors. 1,12-Dodecanedithiol was used as a hydrophobic, flexible linker compound. For comparison, [4]-staffane-3,3'''-dithiol provided a rigid, rodlike linkage, and 4,4'-terphenyldithiol was used as a rigid linker with enhanced conductivity due to its delocalized aromatic moieties. As determined by AFM, all three sensor coatings had similar thicknesses (similar to 30 nm), but the degree of interlinkage, as measured by XPS, was significantly higher in the case of the flexible network. All three materials showed linear current-voltage characteristics. The vapor sensitivity was tested by dosing the sensors with toluene, 1-propanol, 4-methyl-2-pentanone, and water in the concentration range 100-5000 ppm at 0% relative humidity. The flexible 1,12-dodecanedithiol interlinked film responded with an increase in resistance to these analytes and with the highest sensitivity to toluene. In striking contrast, the rigid staffane interlinked film responded with a decrease in resistance to all four analytes and with the highest sensitivity to 4-methyl-2-pentanone. The rigid but more conductive 4,4'-terphenyldithiol interlinked coating gave hardly any response, although microgravimetric measurements showed that similar amounts of analytes were absorbed as in the case of the other two sensor films. The different response characteristics are discussed in terms of film swelling and changes in permittivity.