Development of a novel enzyme-CdS nanoparticle hybrid system for the oxidation of NADH to NAD+

Inorganic semiconductor CdS nanoparticles (NPs) incorporating NADH dehydrogenase (diaphorase: DA) were successfully synthesized using a water-in-oil microemulsion method. The X-ray diffraction pattern of the enzyme-CdS NPs was assigned to a cubic structure CdS phase. The catalytic effect of enzyme-CdS NPs hybrid systems on the oxidation of dihydronicotinamide adenine dinucleotide (NADH) to nicotinamid adenine dinucleotide (NAD+) was investigated. Enzyme-CdS NPs incorporating DA and ferrocene-modified polyethylenimine (Fc-PEI) (1:0.2, w/w) exhibited a significantly increased rate of NADH oxidation under illumination compared with pure CdS NPs. The redox mediator Fc-PEI acted to transfer electrons between the valence band of the CdS NPs and the flavin-bound enzyme during the oxidation reaction. Switchable oxidation of NADH in a colloidal solution of the enzyme-CdS NPs was induced with respect to the dark/light cycle. The catalytic properties of the present CdS NPs activated with an enzyme towards NADH oxidation might have future importance in biochemistry and medical applications.