Metal-Conductive Polymer Core-Shell Nanowires: Electroless Reduction of Pd and Cu On Polypyrrole/DNA Templates Bearing 2-2'-Bipyridyl Groups

Abstract

A method for the preparation of conductive polymer nanowires bearing metal ion chelating 2,2’-bipyridyl groups is described. N-(3-pyrrol-1-yl-propyl)-2,2'-bipyridinium hexafluorophosphate (NP2PBH) was templated on λ-DNA in aqueous solution using FeCl3 as oxidant to initiate polymerization. The polyNP2PBH/DNA nanowires were then decorated with metals (Cu or Pd) by electroless deposition [Cu(NO3)2/ascorbate or PdCl42-/NaBH4]. UV-vis absorption spectra of the hybrid materials show the absorption peak due to the plasmon resonance of Cu at about 550 nm and a broad continuous band consistent with metallic Pd in the range 300−700 nm. The morphology, size and electrical properties of the hybrid nanostructures have been characterized using scanning probe techniques (atomic force microscopy (AFM), scanning conductance microscopy (SCM) and conductive atomic force microscopy (cAFM)). The polyNP2PBH/DNA nanowires show a continuous, smooth and uniform appearance (mean diameter 5.0 nm). Cu deposits on polyNP2PBH/DNA nanowires by a nucleation and growth process that leads eventually to smooth, conductive Cu nanowires. In contrast, Pd deposits in a non-uniform manner on polyNP2PBH/DNA and has inconsistent electrical conductivity. The electrical conductivity of single Cu/polyNP2PBH/DNA nanowires was estimated to be 1.6 ± 0.27 S cm-1 which we suggest is limited by electron transfer between Cu grains.