POTENTIAL DEPENDENCE OF THE CONFORMATIONS OF NICOTINAMIDE ADENINE-DINUCLEOTIDE ON GOLD ELECTRODE DETERMINED BY FT-NEAR-IR-SERS

High-quality Fourier transform surface-enhanced Raman scattering (FT-S ERS) of a dilute solution of nicotinamide adenine dinucleotide (NAD) w as recorded on a roughened Au electrode. It was found that the detecti on limit-could be lower as much as 3 orders of magnitude by using a ne ar-infrared laser as the exciting source and an in-situ roughening tec hnique. The SERS of NAD shows a strong potential dependence in the non -Faradaic regions. In regions of positive electrode potential, only th e bands responsible for the adenine and nicotinamide moieties can be o bserved. In contrast, with a negative shift of the potential, several additional strong bands representing the ribose and phosphate moieties are also evident. Based upon the SERS behaviors of NAD in the regions of different potential, an adsorption mechanism for dilute NAD on the gold electrode was proposed. With this mechanism, the stacked NAD mol ecule is considered to be opened to some extent on an electric charged electrode. Specifically, under sufficiently negative potential, the N AD molecule appears to exist in a well-extended state on the gold elec trode, leading to the tight adsorption of the entire NAD molecule on t he electrode.