Development of Biosensor for Determination of Cd(11) and Hg(11) Ion by Exploiting MWCNT/Peptide Nanohybrid Modified Au Electrode

A biosensor for simultaneous detection of Cd(II) and Hg(II) was developed by using MWCNT/peptides modified Au electrode using cyclic voltammetry (CV). It was observed that the MWCNT/peptide modified gold electrode has significant superior analytical performance in determination of Cd(II) and Hg(II) compared to the unmodified gold electrode. The gold electrode surfaces are modified with peptides that were synthesized by self assembly of cysteine monomers in the presence of diphenylphosphoryl azide (DPPA). This self assembly approach leads to rapid access of cyclic dimer and linear tripeptide of cysteine. The yielded peptides together with the MWCNT are attached to the Au electrode for further characterization and optimization with CV. The experimental conditions such as pH, supporting electrolyte, reproducibility and scan rates of the modified Au electrode were optimized. Modification of peptide and MWCNT on the Au electrode surface has increased the sensitivity and selectivity of the electrochemical sensor for simultaneous determination of Cd(II) and Hg(II) ion. The reproducibility of the electrochemical sensor was good with relative standard deviation (R.S.D) value of 2.52%. The linear response for Cd(II)( in presence of borate buffer at pH 3) was obtained in the range of 0.1 ppm to 50.5 ppm whereas for Hg(II)( in presence of acetate buffer at pH 2) the linear response was obtained in the range of 0.1 ppm to 50.0 ppm. The slope value of log Ip versus log v is 0.61-0.85 demonstrate that the modified Au electrode undergoes diffusion-adsorption controlled process. The sensitivity expressed as the slope of linear region of calibration curve was 6 x 10-6 A/ppm in borate buffer (pH 3) and 8 x 10-7 A/ppm in acetate buffer (pH 2). The limit of detection (L.O.D) for Cd(II) is 2.75 x 10-8 M whereas the limit of detection for Hg(II) is 9.07 x 10-10 M. The developed electrochemical sensors were applied in analysis of electroplating and wood industrial waste water for simultaneous determination of toxic metal Cd(II) and Hg(II). The results of the waste water sample analysis based on the developed method showed a comparable result with the ICP-OES method.

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