Nanozymes have gained much attention as a replacement for natural enzymes duo to their unique advantages. Two-dimensional layered double hydroxide (LDH) nanomaterials with high physicochemical plasticity are emerging as the main forces for the construction of nanozymes. Unfortunately, high-performance LDH nanozymes are still scarce. Recently, defects in nanomaterials have been verified to play a significant role in modulating the catalytic microenvironment, thereby improving catalytic performances of nanozymes. Therefore, the marriage between defect engineering and LDH nanozymes is expected to spark new possibilities. In this work, twenty kinds of natural amino acids were separately inserted into the interlayer of CoFe-LDH to obtain defect-rich CoFe-LDH nanozymes. The peroxidase (POD)-like activity and catalytic mechanism of the as-prepared LDH nanozymes were systematically studied. The results showed that the intercalation of amino acids can effectively enhance the POD-like activity of LDH nanozymes owing to the increasing oxygen/metal vacancies. And l-cysteine intercalated LDH exhibited the highest catalytic activity ascribed to its thiol group. As a proof of concept, LDH nanozymes with superb POD-like activity were used in biosensing and antibacterial applications. This work suggests that modulating the catalytic microenvironment through defect engineering is an effective way to obtain high-efficiency POD mimics.

High catalytic efficiency is the continuous pursuit for the preparation of high-performance nanozymes. In this work, a Fe-Ce double variable-valence metals nanozyme (Fe-Ce-MOL) was constructed based on metal–organic layers (MOLs), a class of two-dimensional metal–organic frameworks with ultra-thin structure, for peroxidase (POD) mimicking. Fe-Ce-MOL exhibited significantly enhanced catalytic activity in comparison with that of natural horseradish peroxidase and single variable-valence metal nanozyme (Fe-Zr-MOL). Density functional theory calculations demonstrated that the Fe site of Fe-Ce-MOL had a stronger adsorption effect on H2O2 compared to Fe-Zr-MOL and more heat was released in the catalytic reaction of H2O2, making the reaction easier to occur. Moreover, there was more electron transfer between Fe and Ce double variable-valence metals, also accelerating the catalytic process. These results indicated that the ultra-thin structure of Fe-Ce-MOL provided more catalytic sites and Fe and Ce double variable-valence metals could regulate the process of oxidation–reduction and promote the efficiency of electron transfer synergistically. As a proof of concept, the proposed Fe-Ce-MOL was used in biosensing and antibacterial applications. These results suggested that Fe-Ce-MOL had great potential as a new-generation nanozyme. This work pioneers a new approach for the rational design of highly efficient nanozymes.

Metal-organic framework (MOF)-based nanozymes have aroused wide interest in biocatalysis. In this work, a kind of MOF-based nanozymes were fabricated through a ligand regulation strategy. First, an iron-triazolate (MET(Fe)) nanozyme with the Fe-N structure was synthesized by the solvothermal method. Then, different proportions of the sulfur-containing ligand were introduced by the the mixed-ligand growth method to obtain a series of S-doped MET(Fe) (S-MET(Fe)) nanozymes. The S-containing ligand would competitively coordinate with Fe instead of triazolate, forming a "-C-SO x " bond and thereby resulting in more oxygen defects. The investigation of the catalytic mechanism showed that the doping of S affected the catalytic activity center of Fe, resulting in the generation of medium-spin species of FeIII and more coordination defects, thereby enhancing its catalytic activity. As a proof of concept, the 1/3-S-MET(Fe) nanozyme with outstanding peroxidase-like activity was used in biosensing and in the elimination of bacteria. This study provides new ideas for the design and construction of highly active nanozymes.

The concentration of carcinoembryonic antigen (CEA) is an important indicator for clinical monitoring and diagnosis of tumor. Early sensitive detection of CEA is significant for cancer diagnosis and therapy. In this study, a sensitive electrochemiluminescence (ECL) immunosensor was fabricated based on functionalized metal organic layers (MOLs) for the determination of CEA. In this immunosensor, Au nanoparticles (AuNPs) were grown on ultrathin two-dimensional MOLs via in situ reduction. AuNPs not only can accelerate the electron transfer but also can be used as the labels to conjugate with antibody. The as-prepared AuNPs@Ir-Zr-MOL nanocomposite showed high ECL efficiency and can be used as an ECL emitter owing to the great ECL property of Ir-Zr-MOL. The ECL intensity of AuNPs@Ir-Zr-MOL decreased linearly with the logarithm of CEA concentration in the range from 1.00 pg mL-1 to 100 ng mL-1. And the detection limit was 0.200 pg mL-1 (S/N = 3). What's more, the asprepared immunosensor worked well in human blood samples, showing its potential for real analysis.

A novel nanocomposite consisting of MoS2 and AuNPs was prepared by a simple self-reduction method without a reductant at room temperature. The as-prepared MoS2@AuNP nanocomposites were further used to construct an electrochemical glucose biosensor.

Two-dimensional transition-metal dichalcogenides (TMDs) have attracted widespread interests owing to their attractive physical and chemical properties. In particular, they are especially attractive in the field of electrochemical biosensors. In this study, the properties of TMDs ((molybdenum sulfide (MoS2), molybdenum diselenide (MoSe2) and molybdenum telluride (MoTe2)) on the glucose sensing were explored and compared. Exfoliated MoS2, MoSe2 and MoTe2 nanosheets with basically the same size were fabricated through controlling the ultrasonic power. The structure and morphological characteristics of MoS2, MoSe2 and MoTe2 were examined through scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and powder X-ray diffractometer. Electrochemical properties were analyzed through cyclic voltammetry and differential pulse voltammetry. Results showed that all the three kinds of TMDs can enhance the electroconductibility of the electrodes. When incorporated into the construction of electrochemical biosensors for glucose detection, all of the three kinds of exfoliated TMDs modified electrodes possessed achieved analytical requirements of selectivity, wide linear ranges, as well as low limits of detection and quantification. In particular, MoS2-based biosensor generated a higher specificity and lower detection limit than that of MoSe2 and MoTe2. This is imperative to showcase the real potential of TMDs in electrochemical biosensors.