The electrochemically effective oxidation of NADH has drawn striking attention because it is widely applicable for fabricating biosensors. The mediators are normally used as electron shuttle molecules between the electrode and enzymes. Phenothiazine compounds deserve as suitable mediators due to theirs negative formal potential and large rate constant. For the practical use, both the enzyme and mediator are required to be co-immobilized on the electrode surface. In this study, gold nano-particles modified with thionine (Th+) were immobilized on the surface of the gold electrode by physical adsorption. Th+ was covalently bound to the surface of the gold nano-particles using 3,3'-dithiobis (succinimidyl propionate) (DSP) as a cross linker. The electrochemistry of Th+ modified on the gold nano-particles was characterized by voltammetry. Th+ molecules on the gold nano-particle modified electrodes showed two redox couples at −30mV and 240mV vs Ag/AgCl at pH7. A well-defined peak for the electrocatalytic oxidation of NADH was observed at 240mV. The nano-particle electrodes modified with glucose dehydrogenase (GDH) and Th+ mediators were fabricated and characterized aiming at fabricating a reagentless glucose biosensor. Upon the addition of glucose to the electrochemical cell, the oxidation current dramatically increased due to an electrocatalytic reaction.
