Because of the high catalytic activities and substrate specificity, natural enzymes have been widely used in industrial, medical, and biological fields, etc. Although promising, they often suffer from intrinsic shortcomings such as high cost, low operational stability, and difficulties of recycling. To overcome these shortcomings, researchers have been devoted to the exploration of artificial enzyme mimics for a long time. Since the discovery of ferromagnetic nanoparticles with intrinsic horseradish peroxidase-like activity in 2007, a large amount of studies on nanozymes have been constantly emerging in the next decade. Nanozymes are one kind of nanomaterials with enzymatic catalytic properties. Compared with natural enzymes, nanozymes have the advantages such as low cost, high stability and durability, which have been widely used in industrial, medical, and biological fields. A thorough understanding of the possible catalytic mechanisms will contribute to the development of novel and high-efficient nanozymes, and the rational regulations of the activities of nanozymes are of great significance. In this review, we systematically introduce the classification, catalytic mechanism, activity regulation as well as recent research progress of nanozymes in the field of biosensing, environmental protection, and disease treatments, etc. in the past years. We also propose the current challenges of nanozymes as well as their future research focus. We anticipate this review may be of significance for the field to understand the properties of nanozymes and the development of novel nanomaterials with enzyme mimicking activities.

Nanozymes: Classification, Catalytic Mechanisms, Activity Regulation, and Applications

Nanomaterials-based photothermal therapy and its potentials in antibacterial treatment.

Gold nanoparticles are popularly used in biological and chemical sensors and their applications owing to their fascinating chemical, optical, and catalytic properties. Particularly, the use of gold nanoparticles is widespread in colorimetric assays because of their simple, cost-effective fabrication, and ease of use. More importantly, the gold nanoparticle sensor response is a visual change in color, which allows easy interpretation of results. Therefore, many studies of gold nanoparticle-based colorimetric methods have been reported, and some review articles published over the past years. Most reviews focus exclusively on a single gold nanoparticle-based colorimetric technique for one analyte of interest. In this review, we focus on the current developments in different colorimetric assay designs for the sensing of various chemical and biological samples. We summarize and classify the sensing strategies and mechanism analyses of gold nanoparticle-based detection. Additionally, typical examples of recently developed gold nanoparticle-based colorimetric methods and their applications in the detection of various analytes are presented and discussed comprehensively.

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Gold Nanoparticle-Based Colorimetric Strategies for Chemical and Biological Sensing Applications.

Recent advances in nano-carrier immobilized enzymes and their applications

Infections caused by multidrug resistant bacteria are still a serious threat to human health. It is of great significance to explore effective alternative antibacterial strategies. Herein, carbon-iron oxide nanohybrids with rough surfaces (RCF) are developed for NIR-II light-responsive synergistic antibacterial therapy. RCF with excellent photothermal property and peroxidase-like activity could realize synergistic photothermal therapy (PTT)/chemodynamic therapy (CDT) in the NIR-II biowindow with improved penetration depth and low power density. More importantly, RCF with rough surfaces shows increased bacterial adhesion, thereby benefiting both CDT and PTT through effective interaction between RCF and bacteria. In vitro antibacterial experiments demonstrate a broad-spectrum synergistic antibacterial effect of RCF against Gram-negative Escherichia coli (E. coli), Gram-positive Staphylococcus aureus (S. aureus), and methicillin-resistant Staphylococcus aureus (MRSA). In addition, satisfactory biocompatibility makes RCF a promising antibacterial agent. Notably, the synergistic antibacterial performances in vivo could be achieved employing the rat wound model with MRSA infection. The current study proposes a facile strategy to construct antibacterial agents for practical antibacterial applications by the rational design of both composition and morphology. RCF with low power density NIR-II light responsive synergistic activity holds great potential in the effective treatment of drug-resistant bacterial infections.

Rough Carbon-Iron Oxide Nanohybrids for Near-Infrared-II Light-Responsive Synergistic Antibacterial Therapy.

White-light emitting elastomers (WLEEs) based on stimuli-responsive aggregation-induced emission (AIE) and regulated Förster resonance energy transfer (FRET) have aroused increasing attention due to the demands for wearable optoelectronic devices. Herein, the blue and orange AIEgens with different environmental sensitivities are synthesized and then encapsulated on both sides of nanofibers via side-by-side electrospinning aiming to achieve the Janus WLEEs. After regulating the blue-orange AIEgens ratio, efficient and stable white light emission with a CIE coordinate of about (0.33, 0.31) is achieved at a blue-orange AIEgens mass ratio of 3:1. Besides, the Janus nanofibers (Janus-NFs) also present super stretchability with elongation at the break over 150% and tensile strength close to 7 MPa. The sensitivity of fluorescence for Janus-NFs to its stretching deformation is used to visualize the evolution of the microstructure of nanofibers during stretching. Moreover, the Janus-NFs are also sensitive to HCl and NH3 , of which the fluorescence color would change under HCl and NH3 fuming above 2 and 57 ppm in air, respectively. The promising applications of the white light Janus-NFs in smart fabrics, warning sensors, and anti-counterfeiting packaging are demonstrated. This finding provides an efficient strategy for achieving wearable WLEEs with multiple functionalities, promoting the development of wearable devices.

Janus-Structural AIE Nanofiber with White Light Emission and Stimuli-Response.

Nanoparticle surfactant (NPS) offers a powerful strategy to generate all-liquid constructs that integrate the inherent properties of the NPs into 3D architectures. Here, using the co-assembly of fluorescent polymeric nanoparticles and amine-functionalized polyhedral oligomeric silsesquioxane, the assembly and jamming behavior of a new type of NPS at the oil-water interface is uncovered. Unlike "solid" inorganic nanoparticles, "soft" polymeric nanoparticles can reorganize when jammed, leading to a relaxation and deformation of the interfacial assemblies, for example, the 3D printed sugar-coated haw stick-like liquid tubules. With NPS serving as emulsifiers, stable Pickering emulsions are prepared that can be converted into robust colloidosomes with pH responsiveness, showing numerous potential applications for encapsulation and controlled release.

Hao Yu

Papers

Janus-Structural AIE Nanofiber with White Light Emission and Stimuli-Response.

Interfacial Assembly and Jamming of Soft Nanoparticle Surfactants into Colloidosomes and Structured Liquids.