Covalent organic frameworks (COFs) have recently emerged as very fascinating porous polymers due to their attractive design synthesis and various applications. However, the catalytic application of COF materials as enzymatic mimics remains largely unexplored. In this work, the Fe-porphyrin-based covalent organic framework (Fe-COF) has been successfully synthesized through a facile postsynthetic strategy for the first time. In the presence of hydrogen peroxide (H 2 O 2 ), the Fe-COF can catalyze a chromogenic substrate (3,3′,5,5′-tetramethylbenzidine (TMB)) to produce color, and this just goes to show that it has an inner peroxidase-like activity. Moreover, the kinetic studies indicate that the Fe-COF nanomaterial has a higher affinity toward both the substrate H 2 O 2 and TMB than the natural enzyme, horseradish peroxidase (HRP). Under the optimized conditions, the Fe-COF nanomaterial was applied in a colorimetric sensor for the sensitive detection of H 2 O 2 . The detection range was from 7 to 500 μM, and the detection limit was 1.1 μM. Furthermore, the combination of the Fe-COF with glucose oxidase (GOx) can be implemented to measure glucose by a one-pot method, and the obtained detection range was from 5 to 350 μM; the detection limit was 1.0 μM. It was proved that the sensor can be successfully used to detect the concentration of glucose in human serum samples. As a peroxidase mimic, the Fe-COF exhibits the advantages of easy preparation, good stability, and ultrahigh catalytic efficiency. We believed that the proposed method in this work would facilitate the applications of COF-based composites as enzymatic mimics in biomedical fields.

Carrier generation and migration are both pivotal to photoelectric (PE) response. Formation of a Schottky contact is conducive to promote carrier migration but cannot fundamentally magnify carrier generation, limiting the eventual PE performance. In this work, an Au@Ag/AgI Schottky contact is established by in situ growth of AgI nanotriangles on the surface of Au@Ag nanoparticles (NPs), and PE enhancement of the Schottky contact is realized by regulating localized surface plasmon resonance (LSPR) properties. In comparison with Ag/AgI Schottky contact, assembly of Au NPs in the center of Ag NPs adjusts the dominated LSPR property from hot-electron transfer (HET) to plasmon-induced resonance energy transfer (PIRET). With the concurrent manipulation of HET and PIRET, additional energy can be employed for carrier generation, while photogenerated electrons offset by hot electrons are reduced, which jointly enlarges PE responses of the Au@Ag/AgI Schottky contact up to 4 times. Benefitted from the etching of thiols to Ag-based materials, the Au@Ag/AgI Schottky contact is further applied to the construction of a photoelectrochemical cysteine sensor. This work proposes a general strategy to enhance PE responses of Schottky contacts, which may advance the design of LSPR-related PE systems.

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In this review, the research progress of the sensors based on the DNA-nanozymes were summarized.