Excitation-dependent multiple luminescence emission of nitrogen and sulfur co-doped carbon dots for cysteine sensing, bioimaging, and photoluminescent ink applications

Abstract

The concentration of L-cysteine (Cys), a sulfur-containing amino acid, acts as an indicator and biomarker for various diseases in humans. Therefore, the identification and detection of abnormal concentrations of Cys are critically important for determining human health. In this study, excitation-dependent multiple emission nitrogen and sulfur co-doped carbon dots (NS-CDs) are synthesized using a one-pot hydrothermal method. The prepared NS-CDs exhibit a small particle size, good optical properties with high quantum yield, excellent stability, and excitation-dependent photoluminescence (PL) property. The synthesized NS-CDs display a narrow diameter ranging from 3 to 7 nm with a relatively higher quantum yield (QY) up to 11.4%. Under optimal conditions, these NS-CDs show good selectivity for Cys over other biologically relevant species and even other similar (di)thiols (GSH/DTT). The synthesized NS-CDs show excellent selectivity and sensitivity to Cys, with a low detection limit of 23 nM and a linear detection range from 0 to 10 μM. The NS-CDs and NS-CDs/Cys are used for cell imaging, showing low toxicity to HCT116 cells and exhibits green fluorescence when observed by confocal microscopy. Furthermore, the controllable and strong photoluminescent emission properties of the NS-CDs and NS-CDs/Cys are visualized as green photoluminescent ink under UV light illumination. The present study is an attractive and innovative perception into the biomedical applications of NS-CDs with controllable photoluminescence.