Optical detection of NADH based on biocatalytic growth of Au-Ag core-shell nanoparticles.

We have developed an optical assay for NADH (Dihydronicotinamide adenine dinucleotide) based on the catalytic growth of gold–silver core–shell nanoparticles (Au–Ag–CSNPs). The nanoparticles were immobilized on pretreated glass slide and are shown to catalyze the NADH-mediated reduction of Ag(I) ions in the presence of 1,4-benzoquinone and cetyltrimethyl ammonium ion. This leads to the formation of Au–Ag–CSNPs on the glass. The absorption peak of the Au–Ag–CSNPs at 415nm increases with the concentration of NADH in the solution used, and this can be measured by UV–vis photometry. High-resolution scanning electron microscopy analysis of the morphology of the surface of the Au–Ag–CSNPs before and after the catalytic reaction revealed a growth of their diameter. Under optimal conditions, NADH can be determined in the concentration range from 0.2 to 3.2mM, and the detection limit is 15.6μM. The sensor has good precision and good storage stability, simple in operation, and can be fabricated at low costs, which made it suitable for the determination of NADH in complex biological systems and in related degradation processes of contaminants.