MXene-based nanomaterials with enzyme-like properties for biomedical applications.

Recently, great progress has been made in nanozyme research due to the rapid development of nanomaterials and nanotechnology. MXene-based nanomaterials have gained considerable attention owing to their unique physicochemical properties. They have been found to have high enzyme-like properties, such as peroxidase, oxidase, catalase, and superoxide dismutase. In this mini-review, we present an overview of the recent progress in MXene-based nanozymes, with emphasis on their synthetic methods, hybridization, bio-catalytic properties, and biomedical applications. The future challenges and prospects of MXene-based nanozymes are also proposed.

Versatile gold-silver-PB nanojujubes for multi-modal detection and photo-responsive elimination against bacteria.

Bacterial infections have become a serious threat to global public health. Nanomaterials have shown promise in the development of bacterial biosensing and antibiotic-free antibacterial modalities, but single-component materials are often less functional and difficult to achieve dual bacterial detection and killing. Herein, we report a novel strategy based on the effective integration of multi-modal bacterial detection and elimination, by constructing the versatile gold-silver-Prussian blue nanojujubes (GSP NJs) via a facile template etching method. Such incorporation of multi-components involves the utilization of cores of gold nanobipyramids with strong surface-enhanced Raman scattering (SERS) activity, the shells of Prussian blue as both an efficient bio-silent SERS label and an active peroxidase-mimic, and functionalization of polyvinyl pyrrolidone and vancomycin, respectively endowing them with good colloidal dispersibility and specificity against S. aureus. The GSP NJs show operational convenience in the SERS detection and excellent peroxidase-like activity for the sensitive colorimetric detection. Meanwhile, they exhibit robust near-infrared photothermal/photodynamic effects, and the photo-promoted Ag+ ions release, ultimately achieving a high antibacterial efficiency over 99.9% in 5 min. The NJs can also effectively eliminate complex biofilms. The work provides new insights into the design of multifunctional core-shell nanostructures for the integrated bacterial detection and therapy.

Mo@ZIF-8 nanozyme preparation and its antibacterial property evaluation.

Types of nanozymes can produce free radicals and/or reactive oxygen species (ROS) to serve as broad spectrum antibacterial materials. Developing nanozyme-based antibacterial materials with good biocompatibility exhibits promising application prospects. In this study, we doped Mo to ZIF-8 (both components have good biocompatibility) to prepare a new nanozyme, Mo@ZIF-8, which can produce hydroxyl radicals (•OH) triggered by a low dosage of hydrogen peroxide (H2O2), exhibiting effective antibacterial capability against both Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus). This work provides a reference for the design of antibacterial nanozymes with good biocompatibility.

Plasmon-enhanced photothermal properties of Au@Ti3C2Tx nanosheets for antibacterial applications.

Antibiotic-resistant bacterial strains have become an ever-increasing public concern due to their significant threats to health safety. Nanomaterial-based photothermal treatment has shown potential in antibacterial applications, but many nanomaterials exhibited limited photothermal activity that may compromise their antibacterial efficacies. Herein, we report a novel strategy based on efficient photothermal ablation and physical contact over a supported nanostructure by loading Au nanoparticles (NPs) on few-layered Ti3C2Tx nanosheets (NSs) for antibacterial treatment. Ti3C2Tx NSs are delaminated via etching and sonication, and act as a reductant for the in situ reduction of HAuCl4·xH2O, producing "naked" Au NPs without any stabilizers. Meanwhile, by adjusting the Au/Ti ratio, the size and loading of the Au NPs are finely regulated, thereby providing an ideal model of a surface-clean Au@Ti3C2Tx heterostructure for probing the composition-performance relationship. Upon irradiation with visible light, it exhibits synergistically enhanced photothermal conversion efficiency and stability, owing to the localized surface plasmonic resonance effect of Au NP and Au-NS interactions. Moreover, under visible light irradiation for 10 min, the Au@ Ti3C2Tx heterostructure exhibits excellent antibacterial activity for Gram-positive S. aureus and Gram-negative E. coli, and kills over 99% bacteria with a low dose of the nanomedicine suspension (50 µg mL-1). The work demonstrates that the incorporation of transition metal carbides with plasmonic metal nanostructures is an effective strategy to enhance the photothermal antibacterial efficacy.

Tumor-Microenvironment-Responsive Cascade Reactions by a Cobalt-Single-Atom Nanozyme for Synergistic Nanocatalytic Chemotherapy.

Nanocatalytic therapy, involving the nanozyme-triggered production of reactive oxygen species (ROS) in the tumor microenvironment (TME), has demonstrated potential in tumor therapy, but nanozymes still face challenges of activity and specificity that compromise the therapeutic efficacy. Herein, we report a strategy based on a single-atom nanozyme to initiate cascade enzymatic reactions in the TME for tumor-specific treatment. The cobalt-single-atom nanozyme, with Co-N coordination on N-doped porous carbon (Co-SAs@NC), displays catalase-like activity that decomposes cellular endogenous H2 O2 to produce O2 , and subsequent oxidase-like activity that converts O2 into cytotoxic superoxide radicals to efficiently kill tumor cells. By incorporation with doxorubicin, the therapy achieves a significantly enhanced antitumor effect in vivo. Our findings show that cascade TME-specific catalytic therapy combined with chemotherapy is a promising strategy for efficient tumor therapy.

Magnet-assisted electrochemical immunosensor based on surface-clean Pd-Au nanosheets for sensitive detection of SARS-CoV-2 spike protein.

Tracking and monitoring of low concentrations of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can effectively control asymptomatic transmission of current coronavirus disease 2019 (COVID-19) in the early stages of infection. Here, we highlight an electrochemical immunosensor for sensitive detection of SARS-CoV-2 antigen marker spike protein. The surface-clean Pd-Au nanosheets as a substrate for efficient sensing and signal output have been synthesized. The morphology, chemical states and excellent stable electrochemical properties of this surface-clean heterostructures have been studied. Functionalized superparamagnetic nanoparticles (MNPs) were introduced as sample separators and signal amplifiers. This biosensor was tested in phosphate buffered saline (PBS) and nasopharyngeal samples. The results showed that the sensor has a wide linear dynamic range (0.01 ng mL-1 to 1000 ng mL-1) with a low detection limit (0.0072 ng mL-1), which achieved stable and sensitive detection of the spike protein. Therefore, this immunosensing method provides a promising electrochemical measurement tool, which can furnish ideas for early screening and the reasonable optimization of detection methods of SARS-CoV-2.

Zero-Dimensional/Two-Dimensional AuxPd100-x Nanocomposites with Enhanced Nanozyme Catalysis for Sensitive Glucose Detection.

Here, we report facile fabrication of two-dimensional (2D) Pd nanosheet (NS)-supported zero-dimensional (0D) Au nanoparticles via galvanic replacement. In the synthesis, the surface-clean Pd NSs premade not only acted as a sacrifice template for replacing Pd atoms by Au3+ ions, but served as a support substrate to support Au nanoparticles. The morphology, structure, and composition of products relied on the Au/Pd feed atomic ratio. Interestingly, the as-obtained 0D/2D AuxPd100-x (x = 4.5, 9.8, and 21) nanocomposites showed remarkably enhanced peroxidase-mimic catalysis in the model oxidation reaction, which followed the typical Michaelis-Menten theory. Compared to Pd NSs, the enhanced catalysis of AuxPd100-x was closely related to both the increased specific surface area and the modified electronic structure of Pd NSs, which resulted in a change in the catalytic pathway, that is, from hydroxyl radical generation to rapid electron transfer. The work provides a simple yet efficient avenue to build highly efficient heterogeneous catalysts based on metallic NSs, as exemplified by the superior nanozyme activity of 0D/2D bimetallic nanostructures for glucose detection.