ABSTRACT
In order to bridge AuNPs by material for molecular wires, appropriate chemical bonds are required. S-Au (thiolate) interaction is a widely used strong chemical bond for this purpose, e.g., self-assembled monolayers (SAMs) using alkanethiol compounds. Thiophenes that include sulfur in their structure also form weak bond with gold. Oligothiophene is reported to form SAMs on flat Au(111) surfaces by immersing a substrate into chloroform solution containing oligothiophene.7,8 Moreover, thiophenes, P-type organic semiconductors that have delocalized p electrons, are expected to serve as electron donors in CT complex. Such CT complex formation can be confirmed through transmittance change (CT absorbance ) or fluorescence quenching.Oligothiophene (Et-6T-Et) and poly (3-hexyl-thiophene) (P3HT) are used for a bridging molecular wire that works as an electron donor to target analytes. Oligo/poly-thiophene bridges can be easily formed by immersion of AuNP nanogap electrode into a thiophene solution. The immersion without oligothiophene is destructive process for nanogap electrode. Another advantage of the surface modification by nanoparticle bridging is that the properties of nanoparticles such as resistance or transmittance spectra (color of the electrode) can be stabilized. 16.2 AuNP Nanowire SensorThe change of the conductance of the nanowire sensor surface induced by some volatile compounds was measured. The fabricated nanowire sensor electrodes were kept in the air with sample gases for 1 min, and then their sheet resistance was measured.9The results are shown in Fig. 16.4. An increment of conductance was observed after exposure to representative acceptor iodine and acetic acid that has an electron-accepting functional group-COOH. Air and evaporated water made the resistance higher compared with that before the exposure. In the case of aniline, which contains electron-donating group –NH2, the resistance also increased. Nitro group –NO2 is an electron-accepting group; therefore, aromatic nitro compounds (DNT and nitrobenzene) decreased sheet resistance of nanowire electrode. This result indicates a possibility of detecting
aromatic nitro compounds with this oligothiophene wire network sensor.
