Aggregation-Induced Emission Carbon Quantum Dots for High-Resolution Cellular Imaging with Superior Fluorescence

Conventional fluorescent probes for cellular imaging face significant limitations, including photobleaching, cytotoxicity, and quenching upon aggregation (aggregation-caused quenching, ACQ). While carbon quantum dots (CQDs) offer advantages like low toxicity, their tendency toward ACQ restricts their utility. To address these challenges, novel aggregation-induced emission (AIE)-active carbon quantum dots (AIE-CQDs) were developed using the AIE principle. Synthesized hydrothermally using 2,2′-dithiobisbenzoic acid and melamine, the AIE-CQDs exhibit a unique hydrophobic structure and disulfide (S-S) bonding. Pronounced fluorescence enhancement was enabled upon aggregation due to this design. Spherical morphology (10–20 nm) and heteroatom doping (N, S) were confirmed through structural characterization. A high quantum yield (25.4%), bimodal emission (green: 484.6 nm; red: 608.8 nm), and excellent stability were exhibited by the AIE-CQDs. Minimal cytotoxicity in HeLa cells (> 90% viability at ≤ 8 μg/mL) was observed. Superior live-cell imaging was revealed by confocal laser scanning microscopy, with time-dependent intracellular aggregation, particularly near nuclear membranes, intensifying red fluorescence and achieving high-resolution imaging (0.2 μm). This AIE behavior, driven by restricted molecular motion via S-S bonding and hydrophobic interactions, resulted in an aggregated-to-dispersed fluorescence intensity ratio of approximately 3.5. AIE-CQDs were established as a promising, low-toxicity alternative with enhanced photostability and resolution for advanced cellular imaging.