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...

SWNTs possess intrinsic peroxidase‐like activity, catalyzing the reaction of peroxidase substrate 3,3,5,5‐tetramethylbenzidene (TMB) in the presence of H2O2 to produce a color reaction. Here SWNTs have been used for label‐free colorimetric detection of disease‐associated single‐nucleotide polymorphism with a direct detection limit of 1 nM.

In recent years, colorimetric biosensing has attracted much attention because of its low cost, simplicity, and practicality. Since color changes can be read out by the naked eye, colorimetric biosensing does not require expensive or sophisticated instrumentation and may be applied to field analysis and point-of-care diagnosis. For transformation of the detection events into color changes, a number of smart materials have been developed, including gold nanoparticles, magnetic nanoparticles, cerium oxide nanoparticles, carbon nanotubes, graphene oxide, and conjugated polymers. Here, we focus on recent developments in colorimetric biosensing using these smart materials. Along with introducing the mechanisms of color changes based on different smart materials, we concentrate on the design of biosensing assays and their potential applications in biomedical diagnosis and environmental monitoring.