Electrochemical preparation of polyaniline microspheres incorporated with DNA

Abstract

The conductive polymer polyaniline (PANI) has various useful functions such as redox activity, color and conductivity changes depending on the oxidized state, reversible anion doping/dedoping and acid/base equilibria [1–3]. Some of the functions have already been utilized in devices such as lightweight secondary batteries, electrochromic displays, electromagnetic shielding devices and anticorrosion coatings. It has also been investigated for other practical uses [1–3]. There is no doubt that the morphology control of PANI, in particular, the control of the microand nanostructures, is a significant factor not only its the utilization, but also for the addition of new significant functions. For example, the nanofibrillar morphology improves the performance of PANI in most conventional applications involving polymer interactions with its environment [4]. This leads to much faster and more responsive chemical sensors, new inorganic-PANI nanocomposites and ultrafast nonvolatile memory devices [4]. Microand nanostructures (rods, wires, fibers and tubes) have been obtained using chemical and physical methods. Compared with the physical methods such as electrospinning [5, 6] and mechanical stretching [7], the chemical methods are attractive because there is the probability that they enable the molecular design of PANI. The chemical methods involve templated syntheses, which have been carried out both electrochemically and chemically by polymerizing aniline with the aid of various templates [8–14]. In spite of the variety of current templated syntheses, there is a need for practical synthetic methods capable of preparing pure, uniform, and template-free PANI microand nanostructures in bulk. Deoxyribonucleic acids (DNAs) have been employed as one of the most attractive templates because of their helical molecular structures with negatively charged sites, and several successful examples have been reported [15–20]. In the present study, however, we attempted to employ DNA not as a template, but as an incorporating component with the PANI molecules. It can be expected that, during the oxidative polymerization of aniline, the cationic monomers and oligomers interact with the negatively charged DNA molecules, and a structurally-controlled PANI is obtained. The electrochemical polymerization of aniline in the presence of DNA was performed as a preliminary step to synthesize a structurallycontrolled PANI/DNA composite material. The obtained PANI showed several novel properties versus the ordinary PANI. The PANI was microspheres having a redox activity even in a less acidic aqueous solution and a different absorption band in the visible wavelength range. The PANI microspheres were obtained by a simple electropolymerization.