Fluorescent reversible regulation of cysteamine-capped ZnSe quantum dots successively induced by photoinduced electron transfer of herring sperm DNA and intercalation binding of ethidium bromide.

A fluorescent reversible regulation was studied by fluorescence spectra, ultraviolet-visible spectra in the combination of molecular docking, which based on the photoinduced electron transfer(PET) from hsDNA (herring sperm DNA) to CA (cysteamine)-capped ZnSe QDs (quantum dots) and intercalation of ethidium bromide (EB) into hsDNA. It was proven that the QDs bound with the adding hsDNA by electrostatic force and formed 1:1 hsDNA-QDs complexes, leading to the PET from hsDNA to QDs, and consequently the fluorescence quenching of the QDs; with EB being added in the complex solution, it bound with hsDNA by intercalation interaction and caused hsDNA releasing from hsDNA-QDs complex with forming 2.5:1 EB-hsDNA complex, leading to the recovery of fluorescence, based on the greater binding constant (1.74 × 10 L·mol) of hsDNA with the embedded EB comparing to that of QDs with the captured hsDNA (4.25 × 10 L·mol). A good linear relationship existed between the fluorescence recovery yield and the EB concentrations under the range of 1.0-12.0 × 10 mol·L with bare interference of related substances. This work provided some useful insights into the study of binding mechanism between DNAs with their intercalators and fluorescence bi-direction regulation, and showed great potential for the determination of trace EB.