Effects of crystal structure on the activity of MnO2 nanorods oxidase mimics

The crystal structures would directly affect the physical and chemical properties of the surface of the material,and would thus influence the catalytic activity of the material.α-MnO2,β-MnO2 andγ-MnO2 nanorods with the same morphology yet different crystal structures were prepared and tested as oxidase mimics using 3,3’,5,5’-tetramethylbenzidine(TMB)as the substrate.β-MnO2 that exhibited the highest activity had a catalytic constant of 83.75μmol·m^−2·s^−1,2.7 and 19.0 times of those ofα-MnO2 andγ-MnO2(30.91 and 4.41μmol·m^−2·s^−1),respectively.The characterization results showed that there were more surface hydroxyls as well as more Mn4+on the surface of theβ-MnO2 nanorods.The surface hydroxyls were conducive to the oxidation reaction,while Mn4+was conducive to the regeneration of surface hydroxyls.The synergistic effect of the two factors significantly improved the activity ofβ-MnO2 oxidase mimic.Usingβ-MnO2,aβ-MnO2-TMB-GSH system was established to detect the content of glutathione(GSH)rapidly and sensitively by colorimetry.This method had a wide detection range(0.11-45μM)and a low detection limit(0.1μM),and had been successfully applied to GSH quantification in human serum samples.

Single-atom Pd catalysts as oxidase mimics with maximum atom utilization for colorimetric analysis

Pd-based nanomaterials have shown great promise as potential mimic enzymes,but conventional catalysts use only a small fraction of the Pd content that located on the catalyst's surface.Herein,we demonstrated that maximum atom utilization could be achieved by using single-atom Pd catalysts as oxidase mimic.The single-atom Pd nanozymes exhibit significantly enhanced catalytic efficiency,with a catalytic rate constant(Kcat)and the catalytic efficiency(Kcat/Km)values more than 625 and 4,837 times higher than those of horseradish peroxidase,respectively.A combined experimental and theoretical calculation reveals reactive oxygen species involved catalytic mechanism which endows single-atom Pd catalysts with excellent colorimetric analysis performance.Benefiting from the maximum atom utilization efficiency and well-defined structural features,the single-atom Pd nanozymes could be successfully applied for the total antioxidant capacity of fruit,determining the serum acid phosphatase activity as well as constructing NAND logic gate.This finding not only provides an effective strategy to maximize the noble-metal atom utilization efficiency as enzyme mimics,but also provides a new idea for extending their possible applications.

Ultrathin covalent organic framework nanosheet-based photoregulated metal-free oxidase-like nanozyme

The exploration of low-cost and metal-free nanozymes with oxidase-mimicking activity is highly desired due to their attractive properties and potential applications.However,it is still challenging and remains unexploited to fully realize oxidase-like nanozyme in the emerging covalent organic frameworks(COFs)due to their polymeric nature and weak photoelectric activity.We herein report the first example of the preparation and oxidase-mimicking activity of novel ultrathin two-dimensional(2D)COF(termed as TTPA-COF)nanosheets.The ultrathin TTPA-COF nanosheets with hexagonal layered structure are constructed from two flexible photoactive(diarylamino)benzene-based linkers,and exhibit remarkable catalytic activity toward the oxidation of 3,3',5,5'-tetramethylbenzidine(TMB)in the presence of O_(2) due to their large specific surface areas and abundant active sites.Moreover,it is worth noting that the nanozyme activity could be regulated by external light irradiation.Based on the oxidasemimicking activity of TTPA-COF nanosheets,a green colorimetric sensor is proposed for the sensitive and selective determination of glutathione(GSH)in a wide linear range of 0.5–40μM with a detection limit of 0.5μM.This work reported here would open new avenues for the exploration of low-cost and high-efficiency nanozymes,as well as extend the application of 2D COF nanosheets in the fields of catalysis and sensing.