Microwave-assisted synthesis of green fluorescent copper nanoclusters: a novel approach for sensing of hydroxyl radicals and pyrophosphate ions via a “turn-off–on” mechanism

In the present work, an off–on fluorescent probe based on green light-emitting coffee-trypsin-CuNCs (coffee-Tryp-CuNCs) is developed for the quick, accurate, and targeted detection of ˙OH and pyrophosphate ions (P 2 O 7 4− , PPi). Coffee-Tryp-CuNCs with minimal toxicity and optimal stability were generated by employing a simple and environmentally friendly approach. The fluorescent emission peak of the coffee-Tryp-CuNCs was found to be at 515 nm upon excitation at 430 nm. Hydroxyl radicals (˙OH) selectively decrease the fluorescence intensity of coffee-Tryp-CuNCs, and the quenched fluorescence is recovered in the presence of PPi by a turn-on mechanism. The designed probe exhibits a pH dependent response as a highly acidic environment results in the destruction of the CuNCs due to aggregation. Moreover, the coffee-Tryp-CuNCs were unable to detect ˙OH in acidic conditions (pH 2–6) but as soon as PPi was added to coffee-Tryp-CuNCs-˙OH the fluorescence emission intensity recovers indicating that the pH of the solution affects the detection of ˙OH and PPi. Under the optimized conditions, the detection limits (LOD) for the determination of ˙OH and PPi are estimated as 1.03 μM and 0.68 nM. The probe was used satisfactorily for quantifying ˙OH in tap and industrial water samples.