Red emission B, N, S-co-doped carbon dots with pH-responsive functionality for colorimetric and fluorescent dual-mode detection of Ag+ ions

Novel red-emitting B, N, S-co-doped carbon dots (B,N,S-CDs) were prepared via a one-step hydrothermal carbonization. The obtained B,N,S-CDs are found to be responsive to the pH changes, i.e., the fluorescence intensities obviously change with the watershed of pH 7.4, accompanied by a blue-shift of the fluorescence emission wavelengths with the pH from 1 to 13. The surface state and size of the B, N, S-CDs are responsible for the fantastic responses. Furthermore, introduction of Ag + into the B, N, S-CDs resulted in fluorescence quenching and apparent changes of extinction value, thereby the quantitative assay can be successfully realized where a linear range of 0.1–400 and 0–700 μM with a detection limit of 38 and 107 nM is obtained, respectively. The mechanism might be due to static quenching and induced electron/energy transfer (ET) resulted from the formation of non-fluorescent complex. Strikingly, Ag + can be visualized via evident color changes from red to navy blue under UV light and from maroon to dark brown under sunlight, respectively. These findings indicate that the as-obtained B, N, S-CDs possess a great potential as a dual probe of pH and Ag + ions for biosensing. Graphical Abstract The red-emitting fluorescent B, N, S-CDs with a fantastic pH-sensitive feature, as a dual-mode nanosensor via colorimetric and fluorescence outputs, were applied to detect Ag + ions with the LOD of 107 and 38 nM, respectively.