Xiaogang Qu

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.

Carboxyl-modified graphene oxide (GO–COOH) possesses intrinsic peroxidase-like activity that can catalyze the reaction of peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2 to produce a blue color reaction. A simple, cheap, and highly sensitive and selective colorimetric method for glucose detection has been developed and will facilitate the utilization of GOCOOH intrinsic peroxidase activity in medical diagnostics and biotechnology. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Natural enzymes, exquisite biocatalysts mediating every biological process in living organisms, are able to accelerate the rate of chemical reactions up to 10(19) times for specific substrates and reactions. However, the practical application of enzymes is often hampered by their intrinsic drawbacks, such as low operational stability, sensitivity of catalytic activity to environmental conditions, and high costs in preparation and purification. Therefore, the discovery and development of artificial enzymes is highly desired. Recently, the merging of nanotechnology with biology has ignited extensive research efforts for designing functional nanomaterials that exhibit various properties intrinsic to enzymes. As a promising candidate for artificial enzymes, catalytically active nanomaterials (nanozymes) show several advantages over natural enzymes, such as controlled synthesis in low cost, tunability in catalytic activities, as well as high stability against stringent conditions. In this Account, we focus on our recent progress in exploring and constructing such nanoparticulate artificial enzymes, including graphene oxide, graphene-hemin nanocomposites, carbon nanotubes, carbon nanodots, mesoporous silica-encapsulated gold nanoparticles, gold nanoclusters, and nanoceria. According to their structural characteristics, these enzyme mimics are categorized into three classes: carbon-, metal-, and metal-oxide-based nanomaterials. We aim to highlight the important role of catalytic nanomaterials in the fields of biomimetics. First, we provide a practical introduction to the identification of these nanozymes, the source of the enzyme-like activities, and the enhancement of activities via rational design and engineering. Then we briefly describe new or enhanced applications of certain nanozymes in biomedical diagnosis, environmental monitoring, and therapeutics. For instance, we have successfully used these biomimetic catalysts as colorimetric probes for the detection of cancer cells, nucleic acids, proteins, metal ions, and other small molecules. In addition, we also introduce three exciting advances in the use of efficient modulators on artificial enzyme systems to improve the catalytic performance of existing nanozymes. For example, we report that graphene oxide could serve as a modulator to greatly improve the catalytic activity of lysozyme-stabilized gold nanoclusters at neutral pH, which will have great potential for applications in biological systems. We show that, through the incorporation of modulator into artificial enzymes, we can offer a facile but highly effective way to improve their overall catalytic performance or realize the catalytic reactions that were not possible in the past. We expect that nanozymes with unique properties and functions will attract increasing research interest and lead to new opportunities in various fields of research.

The early detection of cancer can significantly reduce cancer mortality and saves lives. Thus, a great deal of effort has been devoted to the exploration of new technologies to detect early signs of the disease. Cancer biomarkers cover a broad range of biochemical entities, such as nucleic acids, proteins, sugars, small metabolites, and cytogenetic and cytokinetic parameters, as well as entire tumour cells found in the body fluid. They can be used for risk assessment, diagnosis, prognosis, and for the prediction of treatment efficacy and toxicity and recurrence. In this review, we provide an overview of recent advances in cancer biomarker detection. Several representative examples using different approaches for each biomarker have been reviewed, and all these cases demonstrate that the multidisciplinary technology-based cancer diagnostics are becoming an increasingly relevant alternative to traditional techniques. In addition, we also discuss the unsolved problems and future challenges in the evaluation of cancer biomarkers. Clearly, solving these hurdles requires great effort and collaboration from different communities of chemists, physicists, biologists, clinicians, material-scientists, and engineering and technical researchers. A successful outcome will result in the realization of point-of-care diagnosis and individualized treatment of cancers by non-invasive and convenient tests in the future.

Cerium oxide nanoparticles (CeONPs) have received much attention because of their excellent catalytic activities, which are derived from quick and expedient mutation of the oxidation state between Ce4+ and Ce3+. The cerium atom has the ability to easily and drastically adjust its electronic configuration to best fit its immediate environment. It also exhibits oxygen vacancies, or defects, in the lattice structure; these arise through loss of oxygen and/or its electrons, alternating between CeO2 and CeO2−x during redox reactions. Being a mature engineered nanoparticle with various industrial applications, CeONP was recently found to have multi-enzyme, including superoxide oxidase, catalase and oxidase, mimetic properties that produce various biological effects, such as being potentially antioxidant towards almost all noxious intracellular reactive oxygen species. CeONP has emerged as a fascinating and lucrative material in biological fields such as bioanalysis, biomedicine, drug delivery, and bioscaffolding. This review provides a comprehensive introduction to CeONP’s catalytic mechanisms, multi-enzyme-like activities, and potential applications in biological fields. Cerium oxide nanoparticles have the unique power to act as both oxidation and reduction catalysts, thanks to the ability of cerium to rapidly switch between two oxidation states. Can Xu and Xiaogang Qu from the Chinese Academy of Sciences review how this dual catalytic activity yields enzyme-like behavior that can be harnessed for cancer-detecting assays and new biomedical applications. The nanoparticles mimic enzyme species, such as superoxide dismutases and catalases, that repair the damage caused by free radicals and reduce harmful reactive oxygen levels in the body. With tiny dimensions that allow them to enter cellular spaces inaccessible to traditional medicines - including crossing the blood-brain barrier for Alzheimer's disease treatments - these nanomaterials may offer potent remedies against degenerative diseases. Xu and Qu stress the need for systematic biological testing, however, to resolve possible toxicity concerns. Cerium oxide nanoparticles (CeONPs) have attracted much attention because they possess multi-enzyme mimetic properties and have been used in bioanalysis, biomedicine, drug delivery, bioscaffold and so on. This review summarizes recent achievements on CeONPs catalytic mechanisms, the multi-enzyme-like activity, and their biomedical applications, such as in treatment of cancer, diabetes and Alzheimer’s disease.