Facile one‐pot synthesis of PEG‐derived carbon dots with enhanced luminescence via L‐cysteine‐assisted S,N‐doping

Carbon nanodots (C‐dots) are promising photoluminescent nanomaterials for biomedical applications. Among them, PEG‐derived C‐dots demonstrate exceptional photoluminescence and passivation properties, making them particularly attractive for use in the biomedical field. In this article, we present the synthesis of photoluminescent S,N‐doped PEG‐derived carbon dots that are stable at ambient temperature and can be produced using an easy hydrothermal technique. To synthesize the carbon dots, the non‐hazardous polymer polyethylene glycol (PEG) was used as the sole precursor rather than any other potentially hazardous compounds. The absence of L‐cysteine in the reaction mixture resulted in carbon dots with no significant absorbance in the visible region but exhibited photoluminescence properties with a maximum excitation and emission at 343 and 452 nm, respectively. However, the addition of L‐cysteine resulted in a visible absorbance and a red shift in both the maximum excitation and emission, at around 435 and 503 nm, respectively. The Fourier transform infrared spectroscopy (FTIR) analysis provided evidence for the presence of ‐SH, ‐SO2, ‐NH2, and CON‐H bond stretching after the addition of L‐cysteine, suggesting possible S,N‐doping of the carbon dots, which likely caused the observed changes in photoluminescence properties. These findings contribute to the understanding of S,N‐doping in carbon dots and highlight their potential applications in optoelectronics, sensing, and biomedical imaging. S,N‐doped carbon dots were synthesized via a hydrothermal method at a low temperature using PEG 400 as the carbon source. The addition of L‐cysteine to the reaction mixture resulted in the formation of carbon dots with enhanced luminescence properties because of the incorporation of S and N functional groups on the surface.