This work was the first to report that the kanamycin-binding DNA aptamer (5′-TGG GGG TTG AGG CTA AGC CGA-3′) can form stable parallel G-quadruplex DNA (G4-DNA) structures by themselves and that this phenomenon can be verified by nondenaturing polyacrylamide gel electrophoresis and circular dichroism spectroscopy. Based on these findings, we developed a novel label-free strategy for kanamycin detection based on the G4-DNA aptamer-based fluorescent intercalator displacement assay with thiazole orange (TO) as the fluorescence probe. In the proposed strategy, TO became strongly fluorescent upon binding to kanamycin-binding G4-DNA. However, the addition of kanamycin caused the displacement of TO from the G4-DNA–TO conjugate, thereby resulting in decreased fluorescent signal, which was inversely related to the kanamycin concentration. The detection limit of the proposed assay decreased to 59 nM with a linear working range of 0.1 μM to 20 μM for kanamycin. The cross-reactivity against six other antibiotics was negligible compared with the response to kanamycin. A satisfactory recovery of kanamycin in milk samples ranged from 80.1% to 98.0%, confirming the potential of this bioassay in the measurement of kanamycin in various applications. Our results also served as a good reference for developing similar fluorescent G4-DNA-based bioassays in the future.

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Nanozymes are emerging nanomaterials with ideal enzymatic catalytic performance. The development of nanozymes has been shown clear potential to overcome the limitations of natural enzymes such as troublesome preparation, ease of denaturation, high price, and difficulty of recycling. Since the discovery of magnetic Fe 3 O 4 nanoparticles with intrinsic peroxidase-like activity in 2007, the researches on nanozymes have been booming in the next decade. According to the unique nanoscale effect, nanozymes show prominent catalytic performance, which enables them to be applied in various fields of biomedical engineering. In this review, we mainly focus on the catalytic therapeutics of nanozymes in combating bacteria, cancer therapy, alleviating inflammation and neuroprotection.