One-step sonochemical synthesis of versatile nitrogen-doped carbon quantum dots for sensitive detection of Fe2+ ions and temperature in vitro

Fluorescent carbon quantum dots (CQDs) can be prepared by sonochemistry with low cost and high efficiency. However, ultrasonic synthesis of CQDs with responsive fluorescence towards environmental stimuli remains a big challenge. Herein, we report a simple one-step method to fabricate versatile nitrogen-doped CQDs (NCQDs) by ultrasonic treatment of dopamine in dimethylformamide for 8 h. The obtained NCQDs simultaneously possess superior water dispersibility and stability, bright and stable fluorescence against variations of pH and ionic strength, low cytotoxicity and high photostability. Moreover, the fluorescence of NCQDs showed sensitive quenching phenomenon towards Fe2+ ions both in water and in the interior of cancer cells. The emission intensity of NCQDs exhibited good linear relationship (R-2 = 0.9987) with the concentration of Fe2+ ions in the range of 0-50 mu M. The limit of detection can reach as high as 38 nM. Meanwhile, the NCQDs also exhibited temperature-dependent fluorescence with favorable linear relationship (R-2 = 0.9965) in the range of 283-358 K, and thus can server as a nanothermometer to sense temperature both in water and in cells.