Quest for the quenching and binding mode of functionalized ZnO QDs with calf thymus DNA: Biophysical and in silico molecular modelling approach

Abstract

The effect of capping on zinc oxide (ZnO) quantum dots (QD)upon its interaction with calf thymus DNA (ct-DNA) in vitro have been examined using different specrtroscopic techniques. The experimental results elucidate two possible binding modes between ZnO QDs and ct-DNA. The quenching mechanism of QDs in presence of DNA revealed that although two types of quenching is possible but overall quenching is dominated by complex formation (i.e. static quenching) over dynamic collision (i.e. dynamic quenching). In our steady state absorption and fluorescence experiments the binding constant came up in the order of 104 L mol−1 which is an indicator of intercalation. The competitive displacement assay, CD spectral analysis, iodide quenching further reflect threaded intercalation between QDs and ct-DNA. Here, most of the QDs may bind to the DNA as groove binder and the rest as intercalator. Time-resolved measurements and in silico experiments also confirmed our conclusion. Usually, the size of QDs compels itself to bind as groove binder with ct-DNA, but in our study, we have detected that after suitable capping QD can behave as a mixed binder with ct-DNA. As QDs are frequently used as a drug carrier, this study will help in drug designing research.