NAD(+)/NADH-sensitive quantum dots: applications to probe NAD(+)-dependent enzymes and to sense the RDX explosive

Phenyl boronic acid-functionalized CdSe/ZnS quantum dots (QDs) were synthesized. The modified particles bind nicotinamide adenine dinucleotide (NAD(+)) or 1,4-dihydronicotinamide adenine dinucleotide (NADH). The NAD(+)-functionalized QDs are effectively quenched by an electron transfer process, while the NADH-modified QDs are inefficiently quenched by the reduced cofactor. These properties enable the implementation of the QDs for the fluorescence analysis of ethanol in the presence of alcohol dehydrogenase. The NADH-functionalized QDs were used for the optical analysis of the 1,3,5-trinitrotriazine, RDX explosive, with a detection limit that corresponded to 1 x 10(-10) M. We demonstrate cooperative optical and catalytic functions of the core-shell components of the QDs in the analysis of RDX.