One-Step Synthesis of Label-Free Ratiometric Fluorescence Carbon Dots for the Detection of Silver Ions and Glutathione and Cellular Imaging Applications

The construction of ratiometric fluorescence assay has displayed fantastic advantages in improving semi-quantitative visualization capability by presenting successive color changes. Herein, long-wavelength emission nitrogen-doped carbon dots (N-CDs) were developed for intrinsic ratiometric detection of silver ions (Ag⁺) and glutathione (GSH), accompanied by visualization fluorescence variation of orange and green. The label-free N-CDs were favorably obtained through one-step hydrothermal synthesis and displayed single long-wavelength emission at 618 nm under the excitation wavelength of 478 nm. Interestingly, a ratio rising peak emerges at 532 nm and the emission at 618 nm decreases with the introduction of Ag⁺, which exhibits ratiometric fluorescence emission characteristics ( I_618nm/ I_532nm) in the range of 0-140 μM with significant fluorescence varying from orange to green. Furthermore, the fluorescence of CDs@Ag(I) can be effectively ratiometric recovered by virtue of a specific reaction of GSH with Ag⁺, which is accompanied by the fluorescence of the solution returning from green to orange. In addition, the N-CDs hold excellent biocompatibility which can be implemented as the visualization biosensing platform for intracellular determination of Ag⁺ and GSH, demonstrating that proposed N-CDs have tremendous potential in biological systems.