Lysosome-targeted red-fluorescent carbon dots for turn-on detection of permanganate and pH in vivo and in vitro

Rapid, reliable, and convenient fluorescent probes are of great importance for specifically identifying permanganate and pH in biological systems. In this work, raw materials were provided by malic acid and neutral red for the preparation of red emission carbon dots (RCDs) using a hydrothermal carbonization approach. Superior features of RCDs including good stability, exceptional biocompatibility, and prominent water solubility were found, which enables them to favorably track permanganate and pH. Upon the introduction of permanganate, as-acquired RCDs presented a notable emission enhancement owing to aggregation induced emission (AIE) mechanism. Results indicated that they can act as “turn-on” fluorescent sensor for quantitative analysis of permanganate in the scope of 0–115 μM with a detection limit of 14.5 nM. Most importantly, this probe exhibited a special responsive functionality towards pH, in which a good linearity in the pH range of 6.2–8.2 could be readily realized. Besides, evident color changes of RCDs solution under sunlight can be visualized at different pH, which is more desirable for the fluorescent and colorimetric bimodal sensing of pH. Intriguingly, it was observed that RCDs can successfully target lysosome in living cells. Finally, as-developed RCDs were performed for the label-free, real-time visualization of permanganate and pH fluctuations in vivo and in vitro.