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 R2=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.

► Spectral cross talk of NAD+/NADH with QDs was investigated.
► Quenching in NADH fluorescence followed by enhancement of QDs was observed.
► Formaldehyde was detected at 0.01 ng/mL based on FRET from NADH to QDs.
► This method can be used to monitor and detect dehydrogenases in general.