Carbon dots (CDs) synthesized from biological sources have attracted much interest in bioimaging and biomedical applications due to their excellent biocompatibility, and thus, a facile synthesis of CDs with high fluorescence quantum yield (QY) is requisite for practical applications. In this work, we report a simple, rapid, and green approach to synthesize photoluminescent CDs using eutrophic algal blooms as the carbon source. This method offers a possibility for large scale production of highly luminescent CDs (QY = 13%) with the average particle size ∼8 nm. These CDs are highly water-soluble and exhibit nanosecond fluorescence lifetime with high photostability, luminescence stability in different environments, low cytotoxicity, and excellent cell permeability. Laser scanning confocal microscopy shows the uptake of CDs by MCF-7 cells, and the destined application of these CDs as a potential biomarker is demonstrated.

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.

The green synthesis of carbon dots (CDs) is one of the hot research areas in the present-day context.

N-CDs are synthesized by an outright green method and employed as a selective fluorescent probe for Au3+ ions and is also used as a reducing agent to synthesize AuNPs.

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