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 surface‐controlled electrode process. The surface coverage and heterogeneous electron transfer rate constant ( k s ) of adsorbed redox couple onto CNTs films were about 6.32×10 −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 H 2 O 2 reduction at reduced overpotential. The catalytic rate constant for H 2 O 2 reduction was found to be 2.22(±0.20)×10 4  M −1  s −1 . The catalytic reduction current allows the amperometric detection of H 2 O 2 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 H 2 O 2 determination on the electrodes at pH 7. The modified electrode can be used for monitoring H 2 O 2 without the need for an enzyme or enzyme mimic. The proposed method for rapid amperometric detection of H 2 O 2 is low cost and high throughput. Furthermore, the sensor can be used to any detection scheme that uses enzymatically generated H 2 O 2 as a reactive product in biological systems.