Fluorescent ZnO–Au Nanocomposite as a Probefor Elucidating Specificity in DNA Interaction

摘要

In this work, we report the interaction of a fluorescent ZnO–Au nanocomposite with deoxyribonucleic acid (DNA), leading to AT-specific DNA interaction, which is hitherto not known. For this study, three natural double-stranded (ds) DNAs having different AT:GC compositions were chosen and a ZnO–Au nanocomposite has been synthesized by anchoring a glutathione-protected gold nanocluster on the surface of egg-shell-membrane (ESM)-based ZnO nanoparticles. The ESM-based bare ZnO nanoparticles did not show any selective interaction toward DNA, whereas intrinsic fluorescence of the ZnO–Au nanocomposite shows an appreciable blue shift (Δλmax = 18 nm) in the luminescence wavelength of 520 nm in the presence of ds calf thymus (CT) DNA over other studied DNAs. In addition, the interaction of the nanocomposite through fluorescence studies with single-stranded (ss) CT DNA, synthetic polynucleotides, and nucleobasesucleotides (adenine, thymine, deoxythymidine monophosphate, deoxyadenosine monophosphate) was also undertaken to delineate the specificity in interaction. Aminor blue shift (Δλmax = 5 nm) in the emissionwavelength at 520 nm was observed for single-stranded CT DNA, suggestingthe proficiency of the nanocomposite for discriminating ss and dsCT DNA. More importantly, fluorescence signals from the nano-bio-interactioncould be measured directly without any modification of the target,which is the foremost advantage emanated from this study comparedwith other previous reports. The AT base-pair-induced enhancementwas also found to be highest for the melting temperature of CT DNA(ΔTmCT = 6.7 °C). Furthermore,spectropolarimetric experiments followed by calorimetric analysisprovided evidence for specificity in AT-rich DNA interaction. Thisstudy would lead to establish the fluorescent ZnO–Au nanocompositeas a probe for nanomaterial-based DNA-binding study, featuring itsspecific interaction toward AT-rich DNA.