Rare-earth metal-doped orange emissive photoluminescent carbon quantum dots for highly sensitive detection of Hg2+ ions: Multi-color imaging and real samples

Abstract

A novel praseodymium (Pr³⁺)-doped carbon quantum dots (Pr-CQDs) were synthesized through a solvothermal process using citric acid, glutathione and praseodymium as a precursors. The Pr³⁺ ions were effectively coordinated with the carboxylate groups present on the surface of the CQDs and became integrated into the nano-graphene structure within the carbon core. The Pr-CQDs were sensibly analyzed through several spectroscopic and microscopic techniques, including UV–Vis, photoluminescence (PL), FT-IR spectroscopy, XRD, TEM, and XPS. These Pr-CQDs displayed excellent PL properties, emitting a distinct orange light at 575 nm when excited at 400 nm, achieving a quantum yield of 39.18 %. Morphological investigations showed that the Pr-CQDs were spherical in shape, well-dispersed, and had an average size of 4.94 ± 1.1 nm. Additionally, they exhibited stable PL across a broad pH range and in solutions with varying ionic strengths, demonstrating their robustness under different environmental conditions. When tested as optical sensors, The PL properties of Pr-CQDs displayed remarkable selectivity toward Hg²⁺ ions, which caused significant PL quenching, while other metal ions produced negligible responses. A linear relationship was established between the PL intensity and the concentration of Hg²⁺ ions (0–10 μM), with the sensor showing a detection limit as low as 90.3 nM, indicating high sensitivity. In addition, the biocompatibility of the Pr-CQDs were successfully used to multi-color image live cells as confirmed by a water-soluble tetrazolium salt (WST) assay, supporting their potential for use in biomedical applications. Moreover, the practical application, the Hg²⁺ ions was effectively measured using a spike and recovery method with real water samples.