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A simple and sensitive label-free electrochemical DNA biosensor was proposed for the rapid determination of uric acid (UA) using a carbon nano tube paste electrode (CNTPE) modified with salmon sperm dsDNA. At first, the interaction between UA and the DNA was studied using differential pulse voltammetry (DPV). The addition of the DNA to UA solution resulted in a decrease in the peak current of UA and at the same time, a positive shift in the peak potential indicating an intercalative interaction. Then, the voltammetric response of a DNA-immobilized CNTPE was investigated for the determination of UA. The immobilization of the DNA was carried out using acid-functionalized carbon nanotubes and studied using Fe(CN)6 3−/Fe(CN)6 4− redox indicator. Compared with unmodified CNTPE, the oxidation signal of UA showed a significant increase at the DNA-coated electrode, and shifted to more positive potentials attributed to the pre-concentration of UA at the electrode surface due to interaction with the surface-confined DNA layer. This interaction was used for the fabrication of a simple and sensitive biosensor for determining UA. After the optimization of operational parameters, a linear dependence of the peak current on the UA concentration was observed in the range of 7.0×10−7 to 1.1×10−4 molL−1, with the detection and quantification limits of 1.8×10−7 and 5.8×10−7 molL−1, respectively. The proposed biosensor was successfully applied to validate its capability for the analysis of UA in human serum and urine samples. [ABSTRACT FROM AUTHOR]

Abstract: A highly selective and sensitive carbon paste electrode modified with multi-walled carbon nanotubes and 4-[1-(4-methoxyphenyl) methylidene]-3-methyl-5-isoxazolone was used for accumulation and determination of trace amounts of bismuth using the differential pulse anodic stripping voltammetric method. The analytical procedure consisted of a closed-circuit accumulation step onto the modified carbon paste electrode. An anodic peak related to the oxidation of accumulated Bi(0) on the electrode surface was observed at about −0.05V. The calibration curve was linear in the range of 1–400μgL−1. The limit of detection was 0.2μgL−1 and the relative standard deviations for seven replicated determinations at 30, 100 and 300μgL−1 of bismuth were 3.6, 2.4 and 1.6%, respectively. The modified electrode was applied for the determination of bismuth in pharmaceutical, biological and several water samples. The accuracy and precision of results were comparable to those obtained by the graphite furnace atomic absorption spectroscopy method. [Copyright &y& Elsevier]