Oxidative cleavage-based upconversional nanosensor for visual evaluation of antioxidant activity of drugs

In this work, we reported a simple and effective upconversional nanoprobe for selective detection of hydroxyl radical (OH) and visual evaluation of OH-scavenging activities of drugs for the first time. The upconversion luminescence from NaYF₄:Yb,Er nanoparticles was first quenched by carminic acid (CA) through luminescence resonance energy transfer (LRET) mechanism, and then hydroxyl radical-initiated oxidative cleavage of CA can recover the luminescence by inhibition of LRET. The nanosensors exhibited high selectivity towards other reactive oxygen species and many common metal ions with the detection limit down to 0.21μM, and displayed a relative standard deviation ranging from 1.17% to 3.13%. More attractively, the nanosensors have efficiently avoided the interference of autofluorescence upon near-infrared excitation, and provided a robust platform to study hydroxyl radical scavenging abilities of several common antioxidants such as tannic acid, ascorbic acid and ferulic acid, and visually evaluate antioxidant activities of five traditional Chinese medicines by luminescent images. This newly developed nanosensor could be further exploited for many applications in pharmaceutical, biomedical and environmental engineering areas.