Quantum dots as nano plug-in's for efficient NADH resonance energy routing.

The routing of fluorescent signals from NADH to quantum dots (QDs) has been a subject of extensive research for FRET based applications. In the present study, the spectral cross talk of NAD(+)/NADH with QDs was used to monitor the reaction of NAD(+)-dependent dehydrogenase enzyme. CdTe QD may undergo dipolar interaction with NADH as a result of broad spectral absorption due to multiple excitonic states resulting from quantum confinement effects. Thus, non-radiative energy transfer can take place from NADH to CdTe QD enhancing QDs fluorescence. Energy routing assay of NADH-QD was applied for detection of formaldehyde as a model analyte in the range 1000-0.01 ng/mL by the proposed technique. We observed proportionate quenching of CdTe QD fluorescence by NAD(+) and enhancement in the presence of NADH formed by various concentrations of enzyme (0.028-0.4 U). Hence, it was possible to detect formaldehyde in the range 1000-0.01 ng/mL with a limit of detection (LOD) at 0.01 ng/mL and regression coefficient R(2)=0.9982. Therefore, a unique optical sensor was developed for the detection of the formaldehyde in sensitive level based on the above mechanism. This method can be used to follow the activity of NAD(+)-dependent enzymes and detection of dehydrogenases in general.