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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]

Extra concentrations of hemin are toxic since it may intercalate in lipid membranes and catalyze the formation of hydroxyl radicals resulted in the lysis and death of the cell. So, we have proposed a novel green approach for the determination of hemin in biological samples. Due to the complexity of the matrix of these samples, an efficient extraction procedure has been also involved in the approach. An ammonium-based task-specific ionic liquid containing salicylate anion was synthesized and used for the extraction and pre-concentration of hemin trough a dispersive liquid phase microextraction. Hemin was extracted into a few micro liters of the ionic liquid and so, separated from the sample matrix. Differential pulse voltammetry followed the extraction process for the quantification of hemin in the IL-rich phase separated from the sample and placed on the surface of a glassy carbon electrode. In the presented approach, the ionic liquid was used as both the extracting solvent (due to its polarity and water-immiscibility) and the electrode modifying agent (due to its ionic structure). The peak current obtained from the electrochemical reduction of hemin was used as the analytical signal correlated to the concentration of hemin. Different experimental parameters affecting both the extraction and electrochemical processes were optimized. Under the optimized conditions, a linear concentration range of 0.020–2.60 μM with a detection limit of 3.16 × 10 − 3 μM was obtained. The proposed methodology was successfully applied to the determination of hemin in a mouse serum sample indicating its applicability to complex media. [ABSTRACT FROM AUTHOR]