2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

A Non-Oxidative Sensor Based on a Self-Doped Polyaniline/Carbon Nanotube Composite for Highly Sensitive and Selective Detection of the Neurotransmitter Dopamine

S.R. Ali, Y. Ma, R.R. Parajuli, Y. Balogan, W.Y-C. Lai and H. He
Rutgers University, US

Keywords:
polyaniline, boronic acid, carbon nanotubes, voltammetry, detection of dopamine, Parkinson's disease, ascorbic acid, ascorbate oxidase

Abstract:
The ability to measure the concentration of dopamine sensitively and selectively could potentially be used for molecular diagnosis of Parkinson’s disease. The ability to monitor its concentration in-vivo also benefits in design therapies and evaluating the therapeutic efficacy. However, to design a biosensor capable of measuring dopamine at its site of action is challenging. First of all, the concentration of dopamine in the extracelluar fluid of the caudate nucleus in brains is extremely low (tens of nanomoles for normal person, several nanomoles for parkinson’s patient). The challenge is being magnified for in-vivo measurement because the concentration of ascorbic acid, the main detection interference, is 4 to 5 magnitude higher than dopamine. Current detection techniques, including the enzymatic approaches, all suffered from a common problem, i.e. the oxidation products of dopamine could react with ascorbic acid in the sample, which results in severe interference of the detection. Most of the current detection techniques for in-vivo detection of dopamine exploit the neurotransmitter’s ease of oxidation. However, the oxidative approaches including enzymatic oxidation approaches, suffer from a common problem. The oxidation products of dopamine can react with the electrode surface, which causes electrode fouling. The products can also react with ascorbic acid in samples and regenerate dopamine, which severely limits the potential for accurate detection. In this paper, we report a non-oxidative approach to electrochemically detect dopamine with high sensitivity and selectivity (Figure 1). This approach takes advantage of the high performance of our newly developed poly(anilineboronic acid)/carbon nanotube composite and the excellent permselectivity of the ion-exchange polymer Nafion. The binding of dopamine to the boronic acid groups of the polymer with large affinity affects the electrochemical properties of the polyaniline backbone, which act as the transduction mechanism of this non-oxidative dopamine sensor. The unique reduction capability and high conductivity of single-stranded DNA functionalized single-walled carbon nanotubes greatly improved the electrochemical activity of the polymer in physiologically buffers, and the large surface area of the carbon nanotubes largely increased the density of the boronic acid receptors. The high sensitivity and selectivity of the sensor (Figure 2, 3) show excellent promise toward molecular diagnosis of Parkinson's disease.

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