Rapid detection of silver ions based on luminescent carbon nanodots for multicolor patterning, smartphone sensors, and bioimaging applications.

Photoluminescent nitrogen and sulfur co-doped carbon nanodots (N,S-CNDs) were prepared single-step hydrothermal carbonization using 2,4-diaminobenzenesulfonic acid (2,4-DABSA) as the sole precursor. The synthesized N,S-CNDs are easily dispersed in aqueous solution and have an average particle size of 5.0 ± 0.2 nm, showing a high quantum yield of 23.1% with excellent stability. The surface states of the N,S-CNDs were confirmed by Fourier-transform infrared spectroscopy, powder X-ray diffractometry, Raman spectroscopy, and X-ray photoelectron spectroscopy techniques. These N,S-CNDs were applied for the rapid visual sensing detection of Ag ions, which can be identified by their photoluminescent color change under ultraviolet (UV) light illumination at 365 nm within 5 s. Furthermore, a linear correlation coefficient between / and Ag ions was observed in the linear range of 0-1.2 μM with a detection limit of 7.88 nM. The proposed method was successfully used for the sensitive detection of Ag ions in real samples with satisfactory recoveries and relative standard deviation. The photoluminescence properties of N,S-CND and N,S-CNDs/Ag aqueous solutions were demonstrated by their invisible inks that can only be seen when irradiated with UV light. The RGB values of N,S-CND and N,S-CNDs/Ag aqueous solutions were measured using a color selector smartphone application. In addition, N,S-CND and N,S-CNDs/Ag aqueous solutions were further used for the multicolor imaging of HCT-116 cancer cells due to the low toxicity of N,S-CNDs.