An ultrafast responsive and sensitive ratiometric fluorescent pH nanoprobe based on label-free dual-emission carbon dots

Carbon dots (CDs), as a new kind of fluorescent pH nanoprobe, have attracted significant attention due to their favorable optical properties and excellent environmental friendliness. However, a real ratiometric and self-calibrating fluorescent pH nanoprobe based on intrinsic dual-emission CDs (DECDs) still remains scarce. In this study, we reported a kind of intrinsic DECDs for ratiometric fluorescence pH sensing. Interestingly, the two emission bands at 393 and 580 nm from the DECDs simultaneously display strong pH-dependence but with an adverse variation trend. The ratio of the intensity of 393 and 580 nm matches well with an empirical function against pH in the range from 2.2 to 8.0, and further, an excellent linear relationship is presented in an acidic environment with a responsive pH range of 2.2-4.0. Moreover, the rapid response time (<1 min), high sensitivity, good reversibility and pinpoint accuracy (+/- 1.0%) for pH sensing reveals that the as-prepared DECDs can act as excellent ratiometric luminescent nanoprobes for pH detection. We hope that this study will offer new possibilities for expanding the applications of luminescent CDs in chemical sensing, biomedicine and food safety.