Strategy to synthesize long-wavelength emission carbon dots and their multifunctional application for pH variation and arginine sensing and bioimaging

In this work, we designed N and S co-doped carbon dots (N,S-CDs) with long-wavelength emission and their multifunctional application in pH variation, arginine (Arg) sensing, bioimaging in living cells and zebrafish, and fluorescent materials. The N,S-CDs with excitation wavelength-dependent properties were prepared using neutral red (NR) and dl-methionine (DL-Met) as raw materials by one-pot hydrothermal strategy. The N,S-CDs exhibited a unique pH-sensitive luminescence trait within pH range of 3.2-11.0 and have great linear relationship of 4.8-8.0, which indicating their potential application as an imaging reagent in physiological environments. Arg can quench the PL of N,S-CDs due to static quenching. (SQ). The linear range is 2.5-62.5 μM and the LOD is calculated as 0.68 μM. Furthermore, the as-proposed N,S-CDs can be applied as imaging reagents for monitoring of pH and Arg in vivo and vitro owing to outstanding biocompatibility and low cytotoxicity. Interestingly, the N,S-CDs were also used in fluorescent composite films and phosphors owing to exceptional optical properties. All these results indicate that the N,S-CDs have huge potentiality in the areas of fluorescence sensing, bioimaging and fluorescent materials.