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Electrochemical sensors for the analysis of TNT with enhanced sensitivities are described. The enhanced sensitivities are achieved by tailoring pi-donor-acceptor interactions between TNT and pi-donor-modified electrodes or pi-donor-cross-linked Au nanoparticles linked to the electrode. In one configuration a p-aminothiophenolate monolayer-modified electrode leads to the analysis of TNT with a sensitivity corresponding to 17 ppb (74 nM). In the second configuration, the cross-linking of Au NPs by oligothioaniline bridges to the electrode yields a functionalized electrode that detects TNT with a sensitivity that corresponds to 460 ppt (2 nM). Most impressively, the imprinting of molecular TNT recognition sites into the pi-donor oligoaniline-cross-linked Au nanoparticles yields a functionalized electrode with a sensitivity that corresponds to 46 ppt (200 pM). The electrode reveals high selectivity, reusability, and stability.

Composite materials consisting of polyaniline/poly(4-styrene-sulfonate) (PAn/PSS) or polyaniline/Au nanoparticles capped with 2-mercaptoethane sulfonic acid (PAn/Au-NPs) are prepared in the form of thin films (thickness ca. 90 nm) on Au electrodes or in the form of microrods linked to a Au surface. The composite materials in the microrod structures are electrochemically prepared in porous alumina membranes coated with a Au film, followed by the dissolution of the membrane. Chronoamperometric experiments reveal that the charge transport in the PAn/Au-NPs system is ca. 25-fold enhanced as compared to the analogous PAn/PSS system. The different polyaniline composite assemblies were used as catalysts for the electrochemical oxidation of ascorbic acid and as electron-transfer mediators for the bioelectrocatalytic activation of glucose oxidase (GOx) toward the oxidation of glucose. The PAn/Au-NPs system in the microrod structure reveals superior function as the catalyst for the electrochemical oxidation of ascorbic acid and in the bioelectrocatalytic activation of GOx because of the high surface area of the assembly and the enhanced charge-transport properties of the composite material.

p-Aminothiophenol-capped CdS nanoparticles (8.5 ± 0.3 nm) were assembled as a monolayer by their electropolymerization into a p-aminothiophenol-monolayer-functionalized Au electrode. The resulting CdS nanoparticle monolayer, 9.0 × 1011 particles/cm2, was characterized by AFM, XPS, and microgravimetric quartz crystal microbalance measurements. The dianiline-bridged CdS nanoparticles assembled on the Au electrode revealed highly efficient photoelectrochemical properties in the presence of triethanolamine as sacrificial electron donor. The dianiline bridging unit was found to have an important function in the photocurrent generation. At an applied potential that is more positive than −0.1 V, the dianiline exists in its oxidized state, and it acts as an electron relay that mediates electron transfer from the semiconductor to the bulk electrode. The quantum yield at an applied potential of 0.4 V corresponds to φ = 5.7%. At an applied potential of less than −0.1 V the polymer exists in its reduced state, and under these conditions the dianiline units act as a tunneling medium for transporting the electrons from the semiconductor nanoparticles to the electrode.

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