Nature-inspired design of carbon dots for multifunctional applications in 6-mercaptopurine sensing, bioimaging, and bacterial growth promotion.

6-Mercaptopurine (6-MP) is a thiopurine derivative widely employed in the treatment of certain cancers and autoimmune diseases. Its therapeutic efficacy is contingent upon precise dosing, given its narrow therapeutic index and variability among patients, underscoring the need for reliable monitoring methods. To enable sensitive and cost-effective detection, calcium-, oxygen-, and sulfur-enriched carbon dots (MOG-CDs) were synthesized from Moringa oleifera gum via hydrothermal carbonization. The low-cytotoxic, biocompatible MOG-CDs exhibited aggregation-induced photoluminescence enhancement upon interaction with 6-MP, mediated by heteroatom coordination. The resulting sensor showed high selectivity and sensitivity, with a detection range of 0-10 ppm and a detection limit of 1.07 ppb (6.28 nM). It was used to successfully quantify 6-MP in pharmaceutical tablets and plasma samples from acute lymphoblastic leukemia patients. Integration with a smartphone-based device further demonstrated its potential for portable, resource-limited applications. The photoluminescent and biocompatible nature of MOG-CDs also enables their use in advanced in vitro cellular imaging.