Engineered Bright Blue- and Red-Emitting Carbon Dots Facilitate Synchronous Imaging and Inhibition of Bacterial and Cancer Cell Progression via ¹O₂-Mediated DNA Damage under Photoirradiation

The development of biocompatible, widely applicable fluorescent imaging probe, with emission beyond the cellular and tissue autofluorescence interference, is a challenging task. In this regard, a series of 28 different fluorescent carbon dots (CDs) were synthesized using carbohydrates as carbon and cysteine (Cys) and o-phenylenediamine (OPD) as nitrogen source. The screened CDs showed photostability with bright blue (∼505–520 nm) and red (∼588–596 nm) emission and high fluorescence quantum yield (QY = 72.5 ± 4.5%). FTIR and NMR studies suggested presence of carboxylate and ester group for Cys- and OPD-based CDs, respectively. HRTEM results showed particle size of ∼3.3–5.8 nm for all the developed CDs. The antibacterial studies suggested that the developed CDs showed preferential antibacterial activity against Escherichia coli, with IC50 value of ∼200 μg/mL. Cytotoxicity and confocal microscopy studies of HeLa cells reflected that these CDs showed both anticancer activity and imaging ability. Agarose gel electrophoresis, together with SOSG assay and thiol estimation studies, suggested oxidative stress induced DNA degradation to be the primary cause for cell death. These hemocompatible CDs can thus be used as simultaneous imaging probe and photo dynamic therapeutic agent for both antibacterial and anticancer activity.