Electrochemical detection of nicotinamide adenine dinucleotide based on molecular beacon-like DNA and E. coli DNA ligase

An electrochemical method for nicotinamide adenine dinucleotide (NAD+) detection with high sensitivity and selectivity has been developed by using molecular beacon (MB)-like DNA and Escherichia coli DNA ligase. In this method, MB-like DNA labeled with 5′-SH and 3′-biotin was self-assembled onto a gold electrode in its duplex form by means of facile gold–thiol chemistry, which resulted in blockage of electronic transmission. It was eT OFF state. In the presence of NAD+, E. coli DNA ligase was activated, and the two nucleotide fragments which were complementary to the loop of the MB-like DNA could be ligated by the NAD+-dependent E. coli DNA ligase. Hybridization of the ligated DNA with the MB-like DNA induced a large conformational change in this surface-confined DNA structure, which in turn pushed the biotin away from the electrode surface and made the electrons exchange freely with the electrode. Then the generated electrochemical signals can be measured by differential pulse voltammetry (DPV). Under optimized conditions, a linear response to logarithmic concentration of NAD+ range from 3 nM to 5 μM and a detection limit of 1.8 nM were obtained. Furthermore, the proposed strategy had sufficient selectivity to discriminate NAD+ from its analogues.