One-pot microwave-assisted synthesis of blue emissive multifunctional N-S-P co-doped carbon dots as a nanoprobe for sequential detection of Cr(VI) and ascorbic acid in real samples, fluorescent ink and logic gate operation

In this communication, blue light-emitting fluorescent N-S-P co-doped carbon dots (PGP-CDs) were synthesized by a simple, yet rapid procedure using microwave charring. Low cost, easily accessible precursors like glutathione, polyethylene glycol (PEG-400), and o-phosphoric acid (H3PO4) were used in the synthesis following which PGP-CDs obtained with a good quantum yield (15%) were well characterized. The HRTEM analysis showed that PGP-CDs were well distributed and spherical, with an average size of 4.5 nm. XPS analysis confirmed the chemical composition of doped N-S-P-CDs, and fluorescence spectroscopy revealed that they exhibit pH-independent and excitation wavelength-dependent fluorescence with excitation/emission maxima at 380/455 nm. Blue fluorescence of the PGP-CDs was exclusively quenched by the addition of carcinogenic Cr(VI) in the presence of other metal ions within a linear range of 0.1-100 mu M which can be explained by the inner filter effect (IFE). The regeneration of carbon dots could be achieved by the addition of ascorbic acid (AA) and thus, PGP-CDs act as a sensitive fluorescent turn "on-off-on" nano-sensor in water. The limit of detection (LOD) for Cr(VI) was found to be 4 nM which is lesser than the permissible limit (0.9 mu M) as prescribed by World Health Organisation (WHO) in drinking water. PGP-CDs show reversibility up to four cycles and on this basis, a combinatorial molecular logic gate consisting of a special combination of logic functions NAND & NOT has been constructed. Furthermore, PGP-CDs were also utilized as fluorescent ink without any chemical alteration. For real sample applications, PGP-CDs were also successfully applied to determine Cr(VI) in real water samples and PGP-CD + Cr(VI) complex to detect AA levels in food samples. Results obtained from real sample analysis suggest that PGP-CDs can be used as a potential nanoprobe that offers outstanding precision in detecting the trace amount of Cr(VI) and AA with a low detection limit. (C) 2021 Elsevier B.V. All rights reserved.