Dual-functional carbon dots-silver@zinc oxide nanocomposite: in vitro evaluation of cellular uptake and induction of apoptosis.

Carbon dots (CDs) are novel bioimaging tools with fascinating fluorescence properties. We report here the development of novel CDs decorated on a silver-zinc oxide (CD-Ag@ZnO) nanocomposite (NC) consisting of highly fluorescent CDs and Ag@ZnO. The CD-Ag@ZnO NC was characterized by various analytical techniques. Our work provides an insight into the application of this CD-Ag@ZnO NC in monitoring cellular uptake and mediating apoptotic effects in MCF-7 and A549 cancer cell lines. By monitoring the simultaneous green fluorescence emission of the CDs, the distribution of the CD-Ag@ZnO NC could be followed, eliminating the need to use fluorescent organic dyes. Fluorescence microscopy and atomic absorption spectrometry were used for the qualitative and quantitative assessment of cellular uptake. In vitro studies of cancer cells treated with CD-Ag@ZnO NC revealed concentration-dependent cytotoxic effects via the induction of apoptosis. Fluorescence and scanning electron microscopy were used to study the characteristic nuclear and morphological changes during apoptosis. We used flow cytometry to quantify the reactive oxygen species and the reverse transcriptase polymerase chain reaction to study apoptotic gene expression. The role of reactive oxygen species in eliciting the apoptotic gene cascade was also studied. Intriguingly, the multifunctional CD-Ag@ZnO NC has a tendency to evoke apoptosis while allowing real-time intracellular trafficking, which may be of huge relevance in cancer theranostic applications.