NADH oxidation on screen-printed electrode modified with a new phenothiazine diazonium salt

NADH oxidation catalysts are extremely important in the field of electrochemical biosensors and enzymatic biofuel cells. Based on the growing diazonium chemistry, we synthesized the diazonium salt of the well-known NADH mediator toluidine blue O. The electrochemical reduction of the diazonium moiety by cyclic voltammetry onto a screen-printed electrode leads to an electrocatalyst suitable for the oxidation of NADH. The amperometric response for its oxidation shows a maximal current of 1.2 μA ([NADH] = 100 μM). Based on electrochemical measurements, the surface coverage is found to be 3.78 × 10− 11 mol cm− 2 and the heterogeneous standard rate constant kh is 1.21 ± 0.16 s− 1. The sensitive layer for the oxidation of NADH is improved by electrografting the diazonium salt with a potentiostatic method. Both the surface coverage and the heterogeneous standard rate constant kh are improved and found to be 6.08 ± 0.63 × 10− 11 mol cm− 2 and ~ 5.02 s− 1, respectively. The amperometric response is also improved by an 8 fold factor, reaching 9.87 μA ([NADH] = 120 μM). These remarkably high values for screen-printed electrodes are comparable to glassy carbon electrodes making this method suitable for low-cost bioelectronical devices.