Loquat fruit-based carbon quantum dots as an “ON-OFF” probe for fluorescent assay of MnO4− in waters based on the joint action of inner filter effect and static quenching

As one kind of high nutrition fruits, abandoned loquat causes great waste due to short storage period. For resource utilization, we herein fabricated the loquat fruit-based carbon quantum dots (CQDs) by a facile/green hydrothermal method. The as-fabricated CQDs showed spherical shape with an average size of 4.46 nm, and richness in functional hydroxyl and carboxyl moieties on their surface. Under daylight and UV light, the as-fabricated CQDs displayed light yellow and blue color, respectively, with a fluorescence quantum yield of 10.36%. Upon the addition of MnO4−, the fluorescence intensity of loquat-based CQDs was prominently quenched in a concentration-dependent manner, suggesting the feasibility for constructing a sensitive "ON-OFF" nanoprobe. By virtue of changes in UV-Vis absorption, fluorescence lifetime, Stern-Volmer constant and zeta potential, the MnO4−-triggered quenching mechanisms were attributable to the joint action of inner filter effect and static quenching. Under optimized conditions, the CQDs supplied wide linear range of 0.2–150 μM, low detection limit of 0.06 μM, and high recovery of 96.0–106.0% for MnO4− in environmental waters. Especially, it exhibited the superior selectivity and anti-inference capacity for other commonly existed cations and anions in waters. In contrast to China authentic indirect iodometry method and previously reported approaches, the newly developed "ON-OFF" nanoprobe possesses comparable or even better analytical performance. As far as our information goes, it is the first report on the loquat fruit-based CQDs for successful application in the assay of trace-level MnO4− in environmental waters, thereby showing great potential in conventional monitoring.