Synthesis of carbon quantum dots from neem fruit flesh for dual metal sensing, bioimaging, and antibacterial applications†

This study reports a straightforward one-step synthesis of carbon quantum dots (CQDs) derived from neem fruit flesh, a readily accessible natural biosource. The synthesized neem fruit flesh-derived CQDs (NFF-CQDs) exhibited excellent optical properties with a quantum yield of 0.2209. Their size, functional groups, and surface charge were analyzed using HR-TEM, FT-IR, and DLS. These NFF-CQDs demonstrated dual metal-sensing capabilities: fluorescence enhancement for Al³⁺ ions and fluorescence quenching for Fe³⁺ ions, enabling the selective and sensitive detection of both metal ions at nanomolar concentrations. The Benesi–Hildebrand and Stern–Volmer plots indicated that Fe³⁺ ions bound more strongly than Al³⁺ ions. Additionally, NFF-CQDs exhibited low toxicity in MCF-7 cell bioimaging and enhanced antibacterial activity against E. coli under blue light irradiation.