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 (GOÀCOOH) is shown to possess intrinsic peroxidase-like activity that can catalyze the reaction of peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H 2 O 2 to produce a blue color reaction. A simple, cheap, and highly sensitive and selective colorimetric method for glucose detection has been developed and been used in buffer solution or diluted blood and fruit juice samples. Our work will facilitate the utilization of the intrinsic peroxidase activity of GOÀCOOH in medical diagnostics and biotechnology.As a novel one-atom-thick planar sheet of sp 2 -bonded carbon atoms, graphene has received much attention in recent years in materials science and biotechnology. [1][2][3][4][5][6][7][8][9][10][11] Significant progress has been made for the utilization of graphene in nanoelectronics, [1,3] nanocomposites, [4,5,7] biosensors, [8,9] and drug delivery. [10,11] Production of graphene sheets in bulk quantity and its modification with functional groups to improve water solubility have been recently reported. [6,11] All these achievements provide new insights into the application of this nanomaterial in medical diagnosis and biosensing. Here, we report that carboxyl-modified graphene oxide (GOÀCOOH) has peroxidase-like activity that can catalyze the reaction of peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H 2 O 2 to produce a blue color reaction. Kinetic studies indicate that GOÀCOOH has even higher catalytic activity to TMB than the natural enzyme, horseradish peroxidase (HRP). Like HRP, the catalytic reaction follows a ping-pong mechanism. Further studies indicate that the observed peroxidase-like activity is not related to the trace amount of metal catalyst in the sample but instead is caused by its own intrinsic property. This is evidenced by energy-dispersive X-ray (EDX) analysis.Peroxidase has great potential for practical application and can be used as a diagnostic kit for hydrogen peroxide (H 2 O 2 ) and glucose. For control of diabetes mellitus, it is important for minimizing diabetic complications to maintain blood glucose concentrations within the normal physiological range. [12] Up to now, a number of glucose sensors have been reported. [13][14][15][16][17][18][19][20][21] Among them, horseradish peroxidase (HRP) has been widely used to fabricate sensors for detection of the products of the glucose oxidase. [16][17][18][19][20][21] In comparison with HRP, GOÀCOOH is low-cost, easy to obtain, more stable to biodegradation, and less vulnerable to denaturation. These advantages indicate that GOÀCOOH can be useful in environmental monitoring and medical diagnostics. In this Communication, using GOÀCOOH peroxidase-like catalytic activity and glucose oxidase (GOx), a colorimetric method for glucose detection has been developed (Scheme 1). The results indicate that this method is simple, cheap, and highly sensitive and selective for glucose detection and has been used in buffer solution and diluted blood or fruit juice samples.GO...

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