Synthesis of highly luminescent carbon dots (CDs) from waste materials gains much attention in the current scenario. We have converted waste expanded polystyrene (EPS), a nonbiodegradable environmental pollutant, into multifunctionalized fluorescent CDs. This can be a good scaling up approach for the large-scale synthesis of nitrogen-doped CDs with a high photoluminescence (PL) quantum yield (QY) of ∼20%. The as prepared CDs exhibit excellent water solubility and a longer PL lifetime (in nanoseconds). They also possess excellent photostability, low cytotoxicity, and stable luminescence QY in different solution environments. Selective and sensitive detection of Au3+ ions is demonstrated using these CDs as fluorescence probes, and a LOD of 53 nM is achieved. A detailed investigation revealed that the observed PL quenching is due to “coordination-induced aggregation caused PL quenching” mechanism.

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