N, P, S-doped carbon dots as photoluminescent probe for highly sensitive detection of Cu2+ and Fe3+ ions: Applications in cancer cell imaging and real samples

Abstract

Heteroatom-doped photoluminescent (PL) carbon dots (CDs) have garnered significant attention recently due to their versatile optical properties, making them ideal for use as optical sensors. This research outlines a straightforward one-pot hydrothermal approach for synthesizing nitrogen (N), phosphorus (P), and sulfur (S)-doped carbon dots (NPS-CDs), using remdesivir and thiourea as starting materials. The synthesized NPS-CDs were comprehensively analyzed using various spectroscopic and microscopic methods, such as UV–Vis, photoluminescence (PL), FTIR spectroscopy, XRD, TEM, and XPS. The NPS-CDs showed impressive photoluminescence, emitting green light at 546 nm when excited at 418 nm, with a high quantum yield of 23.2 %. Morphological studies indicated that the NPS-CDs were spherical and well-dispersed, with an average size of 6.0 ± 0.2 nm. Additionally, the NPS-CDs maintained stable photoluminescence over a broad pH range and in solutions with high ionic strength. As optical probes, the NPS-CDs exhibited strong selectivity toward Cu²⁺ and Fe³⁺ ions, showing a significant quenching effect, while other metal ions produced negligible responses, indicating the sensor specificity. A strong linear relationship was observed between the NPS-CDs photoluminescence intensity and the concentrations of Cu²⁺ and Fe³⁺ ions, with detection limits as low as 3.72 nM for Cu²⁺ and 2.98 nM for Fe³⁺ (0–1.0 μM), demonstrating the sensor sensitivity. Biocompatibility was assessed using a WST assay, and the NPS-CDs successfully imaged live cells, suggesting their potential for biomedical applications. This NPS-CDs sensor offers a promising method for detecting Cu²⁺ and Fe³⁺ ions in environmental water samples, combining high sensitivity, selectivity, and biocompatibility, making it a viable option for monitoring metal ion contamination.