Ultra-fast microwave-assisted synthesis of photoluminescent carbon dots with an ultra-high quantum yield for H2O2 detection

The conventional hydrothermal bottom-up synthesis for preparing carbon dots (CDs) usually requires stringent conditions and high energy consumption, whereas the quantum yield (QY) of CDs remains at a relatively low level. Herein, CDs exhibiting strong blue photoluminescence (PL) with an ultra-high QY (up to 94.4%) were prepared via a simple one-step microwave-assisted route using citric acid (CA) and o-phenylenediamine (o-PD) as precursors. The operating conditions, including reaction time, solvent species, amount of solvent, and precursor molar ratio, were optimized. The CDs synthesized within 3.5 min of microwave heating in ethylene glycol (EG) at a CA-to-PD molar ratio of 5:1 exhibited the highest QY (94.4%). A synergistic PL mechanism of the molecule state and carbon core state emissive centers was proposed according to the characterization results of CDs. Moreover, the proof-to-concept H2O2 fluorescent detection performances of the prepared CDs confirmed their great application potential as probe materials. Through directly mixing the CD products and H2O2, a strong PL response could be rapidly detected after merely 1 min, and the detection limit was calculated to be as low as 8.6 nM. Besides, the CDs exhibited high biocompatibility, making them suitable for in-vivo detection of H2O2. Therefore, this work provides a novel and efficient approach for synthesis of ultra-high QY CDs that can be directly applied in biological detection.