Au-nanoparticle-bis-bipyridinium cyclophane superstructures: assembly, characterization and sensoric applications

A three-dimensional conductive superstructure of 12 +/- 1 nm Au-nanoparticles was built up on a conductive (indium-doped tin oxide) glass support by means of alternating treatments with Au-nanoparticle and cyclobis(paraquat-p-phenylene) tetrachloride solutions. The structure was characterized by absorbance spectroscopy (showing layer build-up and interparticle coupling), and cyclic voltammetry of the gold surface and crosslinking bipyridinium units (showing near-monolayer packing of each nanoparticle layer and a ratio of ca. 100 crosslinker molecules for each nanoparticle). The organic crosslinker molecule acts as a receptor for pi-donor substrates, thus causing the concentration of such guests at the conductive superstructured array. This effect facilitates the use of the electrode as an effective sensing matrix for p-hydroquinone, 3,4-dihydroxyphenylacetic acid, dopamine and adrenaline, to concentrations as low as 1 mu M. The sensitivity of the nanostructured array is controlled by the number of receptor/Au-nanoparticle layers associated with the electrode. Control experiments reveal that the superstructured electrode exhibits selectivity which is a consequence of specific interactions between the guests and the receptor, rather than the result of surface area or microenvironmental effects.