Rational design of novel carbon-oxygen quantum dots for ratiometrically mapping pH and reactive oxygen species scavenging

Heteroatom doping except oxygen is the main method to improve the performance of carbon quantum dots (CQDs), the application is also limited by unpredictable biological negative effects and environmental risks from heteroatoms (N/P/S, etc.). To maximize the role of oxygen while avoiding the negative effects of other heteroatoms, herein, we rationally designed and synthesized a new type of carbon-oxygen quantum dots (COQDs) with high fluorescent performance aim to realize pH sensing and reactive oxygen species (ROS) scavenging. The toxicity test results from four levels of bacterias, Hela cells, Daphnia Magna, and zebrafish indicate that the designed COQDs possess high biocompatibility and low environmental risk. Based on the opposing response of COQDs and Rhodamine 6G (Rh 6G) fluorescent signal to pH changes in the range of 6.0–9.0, a COQDs-Rh 6G complex was constructed by combining Rh 6G for ratiometric pH sensing, and a scanning colorimetric analysis model was further developed for the rapid pH judgment of commercially available waters. The proposed COQDs and pH sensing system were also successfully applied for bioimaging and intracellular pH analysis, respectively. More importantly, the designed COQDs also exhibit excellent ROS scavenging ability, which can be used as an effective antioxidant with good biocompatibility.