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.

The ultimate goal of cancer therapy is to eliminate malignant tumors while causing no damage to normal tissues. In the past decades, numerous nanoagents have been employed for cancer treatment because of their unique properties over traditional molecular drugs. However, lack of selectivity and unwanted therapeutic outcomes have severely limited the therapeutic index of traditional nanodrugs. Recently, a series of nanomaterials that can accumulate in specific organelles (nucleus, mitochondrion, endoplasmic reticulum, lysosome, Golgi apparatus) within cancer cells have received increasing interest. These rationally designed nanoagents can either directly destroy the subcellular structures or effectively deliver drugs into the proper targets, which can further activate certain cell death pathways, enabling them to boost the therapeutic efficiency, lower drug dosage, reduce side effects, avoid multidrug resistance, and prevent recurrence. In this Review, the design principles, targeting strategies, therapeutic mechanisms, current challenges, and potential future directions of organelle-targeted nanomaterials will be introduced.

Boosting Cancer Therapy with Organelle-Targeted Nanomaterials.

Over the past ten years, considerable progress has been achieved in the field of nanomaterials-based enzymes (nanozymes). In comparison with natural enzymes, nanozymes demonstrate significant advantages such as facile synthesis procedure, low price, long storage period, and high environmental stability. A variety of nanomaterials including nanocarbons, metals, metal oxides, metal chalcogenides, halogen compounds, metal-organic frameworks (MOFs), and layered double hydroxides (LDHs) have been extensively investigated for enzyme mimicking. In this review, the recent progresses made in the development of the enzymatic properties of these nanozymes have been discussed. We comprehensively discuss strategies to improve catalytic activity and substrate specificity, enzyme-like catalytic mechanism, and novel application of nanozymes in sensing techniques. In addition, the remaining challenges and some future directions have been addressed. With the fast development of nanozyme applications in bioscience and technology, research in this field has become more and more attractive, which is expected to be a long-term exciting subject in the near future.

Functional nanomaterials with unique enzyme-like characteristics for sensing applications

Photothermal conversion efficiency (η) of gold nanorods (GNRs) can be tuned by enlarging the aspect ratio and forming the core–shell structure. Herein, an easy synthesis method is developed to construct the core–shell GNR@LDH nanostructure with GNRs and layered double hydroxides (LDHs). The interaction between Au and LDHs results some electron deficiency on the surface of Au and the more electrons induce more thermal energy conversion. The η value of GNR@LDH can reach up to 60% under the 808 nm laser irradiation, which is a significant enhanced conversion efficiency compared with the reported GNR-based photothermal therapy materials. CTAB (cetyltrimethyl ammonium bromide) can be replaced totally during the synthesis process, and GNRs maintain a good dispersion in LDHs. This core–shell composite GNR@LDH can be applied in photothermal, antibacterial, tumor therapy and biological imaging with low dosage and nontoxicity.

Core-Shell Gold Nanorod@Layered Double Hydroxide Nanomaterial with Highly Efficient Photothermal Conversion and Its Application in Antibacterial and Tumor Therapy.

Gold nanoparticles (AuNPs) is an important kind of nanozymes and a variety of its artificial enzymatic activities have been reported, such as oxidase, peroxidase, and superoxide dismutase. The DNA with poly purine-modified AuNPs shows an enhancement peroxidase activity compared with poly pyrimidine-modified AuNPs. In this work, purine derivatives are modified on the surface of AuNPs. The peroxidase-like activity of AuNPs is dependent on the chemical structure of the molecules capped on the surface. We find that ferric ions can accelerate the mimic enzymatic ability of 2, 6-diaminopurine (DAP) modified AuNPs. The enhanced catalytic activity comes from the synergistic reaction of AuNPs and ferric ions. The cooperative system can be applied to measure hemoglobin and red blood cells in urine with better sensitivity. Generally, there is no or few red blood cells in human urine. The presence of blood in the urine is closely related with serious diseases, for example chronic nephrotic syndrome and urinary system tumors. Compared the commercial urine test paper, the method based on DAP-AuNPs has a good sensitivity and wider quantitative range and will be helpful to do urine test at home.

Jia Huang

Papers

Core-Shell Gold Nanorod@Layered Double Hydroxide Nanomaterial with Highly Efficient Photothermal Conversion and Its Application in Antibacterial and Tumor Therapy.

Accelerating peroxidase-like activity of gold nanozymes using purine derivatives and its application for monitoring of occult blood in urine

Mitochondria-Targeting Polydopamine Nanocomposites as Chemophotothermal Therapeutics for Cancer.