The continuous detection of glucose is significant for revealing its role in neuron protection and for diagnosis of various diseases. In this study, for the first time, a nonenzymatic online optical detection platform (OODP) for glucose measurement in rat brain utilizing the tandem enzyme activity of V2O5 nanobelts is developed. V2O5 nanobelts were synthesized via a facile solvothermal strategy, and for the first time it is found that the V2O5 nanobelts possess dual enzyme-like activity, i.e., glucose oxidase (GOx)-like and peroxidase-like activity, and can act as a “tandem nanozyme”. To investigate the mechanisms of the GOx-like property, we built an adsorption model, and the RPBE density functional calculations indicate that the glucose molecule can be adsorbed on the V2O5 plane. Based on the ability of V2O5 nanobelts to mimick tandem enzymes, a nonenzymatic online optical detection platform (OODP) for the continuous monitoring of glucose in rat brain was designed, which exhibits excellent stability, high selectivity, and a wide linear detection range from 0.2 to 5 mM and records cerebral glucose alterations in the calm/ischemia model. This facile but reliable nonenzymatic online optical glucose measurement compares favorably with natural enzyme-based online electrochemical glucose analytical systems, and its ready adoption by physiologists and pathologists will facilitate the understanding of brain function and the pathogenesis of diabetes.

Artificial nanozymes have been designed to solve the problems of high cost and poor stability involving natural enzymes in analytical applications. Nevertheless, the catalytic efficiency of the nanozyme still needs to be improved so that it can meet the stability and sensitivity requirements of continuous biological detection. We presented an effective tailoring strategy to enhance the enzyme-like activities of Prussian-blue-analog-based nanozymes. Molybdenum-polysulfide-deposited nickel–iron bimetal Prussian-blue-analog-based hollow nanocages (Nanocages) with peroxidase-, catalase-, and laccase-mimicking activities were synthesized. The doping of molybdenum successfully tailored the size, morphology, composition, and complex structure of the Nanocage, and the peroxidase- and laccase-mimicking activities of the Nanocage nanozyme were enhanced by over 37 and 27 times, respectively, compared with pristine Prussian blue analogs. Moreover, in environments of harsh pH, high temperature, and high salt concentration, Nanocages exhibited much higher stability than natural enzymes. The peroxidase- and catalase-mimicking activities were applied to eliminate reactive oxygen species in cells, whereas the laccase-like activity of Nanocages was integrated with an online sensing platform for in vivo and continuous optical hydrogen sulfide monitoring in the brains of living rats. Our findings may provide possibilities for advancing the design strategy of highly active nanozymes as well as nanozyme-based in vivo detection methods and will offer unique opportunities for their involvement in bioanalytical chemistry.

Due to its unique structure and high porosity, metal–organic frameworks (MOFs) can act not only as nanozyme materials but also as carriers to encapsulate natural enzymes and thus have received extensive attention in recent years. However, a few research studies have been conducted to investigate MOF as a template to generate and tune nanozymes in the structure and performance. In this work, the “raisin pudding”-type ZIF-67/Cu0.76Co2.24O4 nanospheres (ZIF-67/Cu0.76Co2.24O4 NSs) were obtained by rationally regulating the weight ratio of ZIF-67 and Cu­(NO3)2 in the synthesis process. Here, ZIF-67 not only acts as a template but also provides a cobalt source for the synthesis of cobalt copper oxide on the surface of ZIF-67/Cu0.76Co2.24O4 NSs with multiple enzyme-like activities. The ZIF-67/Cu0.76Co2.24O4 NSs can mimic four kinds of enzymes with peroxidase-like, glutathione peroxidase-like, superoxide dismutase-like, and laccase-like activities. Based on its laccase-like activity, an online electrochemical system for continuous monitoring of 3,4-dihydroxyphenylacetic acid with good linearity in the range of 0.5–20 μM and a detection limit of 0.15 μM was established. Furthermore, the alteration of DOPAC in the brain microdialysate before and after ischemia of the rats’ brain was also successfully recorded. This work not only raises a new idea for the synthesis of nanozyme materials with multiple enzyme activities but also provides a new solution for the detection of neurotransmitters in living brains.

Nanozymes have been designed to address the limitations of high cost and poor stability involving natural enzymes in analytical applications. However, the catalytic efficiency of the nanozyme still needs to be improved so that it can meet the selectivity and stability requirements of accurate biomolecule analysis. Here, we presented structure defects of metal−organic frameworks (MOFs) as a tuning strategy to regulate the catalytic efficiency of artificial nanozymes and investigated the roles of defects on the catalytic activity of oxidase-like MOFs. Structural defects were introduced into a novel Co-containing zeolitic imidazolate framework with gradually loosened morphology (ZIF-L-Co) by doping cysteine (Cys). It was found that with the increase in defect degree, the properties of materials such as ascorbate oxidase-like, glutathione oxidase-like, and laccase-like were obviously enhanced by over 5, 2, and 3 times, respectively. In-depth structural investigations indicate that the doping of sulfur inducing structural defects which may destroy the equilibrium state between cobalt and nitrogen in 2-methylimidazole and distort the crystal lattice, thereby enhancing the adsorption of oxygen and thus promoting the oxidase-like activity. The ZIF-L-Co-10 mg with enhanced ascorbate oxidase-and laccase-like activity was loaded into a microreactor and integrated into an online electrochemical system (OECS) in the upstream of the detector. This nanozyme-based microreactor can completely remove ascorbic acid, dopamine, and 3,4-dihydroxyphenylacetic acid which are the main interference toward uric acid (UA) electrochemical measurement, and the ZIF-L-Co-10 mg Cys-based OECS system is capable of continuously capturing UA change in rat brain following ischemia−reperfusion injury. Structure defect tuning of ZIF-L-Co not only provides a new regulatory strategy for artificial nanozyme activity but also provides a critical chemical platform for the investigation of UA-related brain function and brain diseases.

A cyclic N‐halamine precursor, 4‐ethyl‐4‐(hydroxymethyl)oxazolidin‐2‐one (EHMO), was synthesized and attached to poly(methylhydrosiloxane) (PMHS) through silane alcoholysis between the OH of EHMO and SiH of PMHS. The alcoholysis product was chlorinated with tert‐butyl hypochlorite to transfer the NH to NCl and obtain an EHMO‐based N‐halamine polysiloxane. The N‐halamine polysiloxane was impregnated into inert polypropylene (PP) fibers and formed a 72 nm coating layer using supercritical carbon dioxide (scCO2) as solvent and swelling reagent at 28 MPa and 50 °C for biocidal application. The overall synthetic procedure and the impregnation process were characterized by FTIR, XPS, and SEM, respectively. The N‐halamine polysiloxane layer on PP imparted potent antibacterial abilities against both Staphylococcus aureus and Escherichia coli while pristine ones did not exhibit noticeable killing activities. Stability tests showed that the N‐halamine polysiloxane layer was resistant to washing cycles, storage, and UV irradiation and the rechlorination of lost chlorines was good. The strategy of using CO2‐philic PMHS as carrier polymer and scCO2 as working solvent for impregnation presents a general and friendly procedure to functionalize inert substrates without the need of chemical linkage and organic solvent. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46624.