Picomolar detection of hydrogen peroxide at glassy carbon electrode modified with NAD+ and single walled carbon nanotubes

Potential cycling was used for oxidation of NAD(+) and producing an electroactive redox couple which strongly adsorbed on the electrode surface modified with single walled carbon nanotubes (SWCNTs). Modified electrode shows a pair of well defined and nearly reversible redox peaks at pH range 1 - 13 and the response showed a surf ace-controlled electrode process. The surface coverage and heterogeneous electron transfer rate constant (k(s)) of adsorbed redox couple onto CNTs films were about 6.32 x 10(-10)) mol cm(-2) and 2.0 (+/- 0.20) s(-1), respectively, indicating the high loading ability of CNTs toward the oxidation product of NAD(+) (2,8-dihydroxy adenine dinucleotide) and great facilitation of the electron transfer between redox couple and CNTs immobilized onto electrode surface. The modified electrode exhibited excellent electrocatalytic activity for H2O2 reduction at reduced overpotential. The catalytic rate constant for H2O2 reduction was found to be 2.22(+/- 0.20) x 10(4) M-1 s(-1). The catalytic reduction current allows the amperometric detection Of H2O2, at an applied potential of -0.25 V vs. Ag/AgCl with a detection limit of 10 pM and linear response up to 100 nM and resulting analytical sensitivity 747.6 nA/pM. The remarkably low detection limit (10 pM) is the lowest value ever reported for direct H2O2, determination on the electrodes at pH 7. The modified electrode can be used for monitoring H2O2 without the need for an enzyme or enzyme mimic. The proposed method for rapid amperometric detection of H2O2 is low cost and high throughput. Furthermore, the sensor can be used to any detection scheme that uses enzymatically generated H2O2 as a reactive product in biological systems.