One pot hydrothermal synthesis of fluorescent NP-carbon dots derived from Dunaliella salina biomass and its application in on-off sensing of Hg (II), Cr (VI) and live cell imaging.

Graphical abstract Highlights • This is first report of synthesis of fluorescent carbon dots from Dunaliella salina. • A-NPCDs were used as fluorescent probe for selective detection of Hg (II), Cr (VI). • A-NPCDs offer excellent multi-color cell imaging. • Limit of detection for Cr (VI) and Hg (II) were 0.018 μM. • MTT assay showed that carbon dots were biocompatible and slightly cytotoxic. Abstract The impact of hazardous chemicals and toxic metal ions in the environment played havoc to the ecosystem. In the present work green chemistry approach was applied for one-step hydrothermal synthesis of nitrogen, phosphorus dual doped carbon dots, utilizing green precursor i.e, biomass of halophilic microalgae Dunaliella salina (algal derived nitrogen phosphorous carbon dots i.e A-NPCDs). Synthesized A-NPCDs were characterized through TEM, FT-IR, P-XRD, DLS and XPS. It showed appreciable optical properties with significant fluorescence quantum yield (8%)and exhibited blue color under UV – light (λ ex = 365 nm). A-NPCDs acted as fluorescent turn off sensor for toxic metal ion such as Hg (II) and Cr (VI) with good selectivity and sensitivity. Interestingly, ANPCDs detected Cr (VI) up to 0.018μM which was below the permissible level of Cr (VI) in drinking water. Such sensing resulted because of combination of inner filter effect and dynamic quenching mechanism. Moreover, it also showed good selectivity (0.018μM) for Hg (II) via dynamic quenching mechanism. MTT assay of A-NPCDs on HEK-293 cell line showed biocompatibility with negligible cytotoxicity. Therefore, these were successfully employed for live cell imaging and intracellular detection of Hg (II) and Cr (VI) in HEK-293 cell line. Thus, green synthesized A-NPCDs may be a good alternative for chemically derived CDs in intracellular detection of Hg (II) and Cr (VI) of a complex biological environment. [ABSTRACT FROM AUTHOR]