Graphene/AuNPs/chitosan nanocomposites film for glucose biosensing.

The signal transduction and enzyme activity were investigated in biosensors based on the glucose oxidase (GOx) and carbon nanotubes (CNT) embedded in a bioadhesive film of chitosan (CHIT) The voltammetric studies showed that, regardless of CHIT matrix, the GOx adsorbed on CNT yielding a pair of surface-confined current peaks at −048 V The anodic peak did not increase in the presence of glucose in an O2-free solution indicating the lack of direct electron transfer (DET) between the enzymatically active GOx and CNT The voltammetric peaks were due to the redox of enzyme cofactor flavin adenine dinucleotide (FAD), which was not the part of active enzyme The presented data suggest that DET may not be happening for any type of GOx/CNT-based sensor The biosensor was sensitive to glucose in air-equilibrated solutions indicating the O2-mediated enzymatic oxidation of glucose The signal transduction relied on the net drop in a biosensor current that was caused by a decrease in a 4-e– O2 reduction current and

/pdf/on-the-direct-electron-transfer-sensing-and-enzyme-activity-4dud2jwcwd.pdf

On the Direct Electron Transfer, Sensing, and Enzyme Activity in the Glucose Oxidase/Carbon Nanotubes System

Biosensors in clinical chemistry - 2011 update.

A review of enzymatic uric acid biosensors based on amperometric detection

This paper describes the modification of microfluidic paper-based analytical devices (μPADs) with chitosan to improve the analytical performance of colorimetric measurements associated with enzymatic bioassays. Chitosan is a natural biopolymer extensively used to modify biosensing surfaces due to its capability of providing a suitable microenvironment for the direct electron transfer between an enzyme and a reactive surface. This hypothesis was investigated using glucose and uric acid (UA) colorimetric assays as model systems. The best colorimetric sensitivity for glucose and UA was achieved using a chromogenic solution composed of 4-aminoantipyrine and sodium 3,5-dichloro-2-hydroxy-benzenesulfonate (4-AAP/DHBS), which provided a linear response for a concentration range between 0.1 and 1.0 mM. Glucose and UA were successfully determined in artificial serum samples with accuracies between 87 and 114%. The limits of detection (LODs) found for glucose and UA assays were 23 and 37 μM, respectively. The enhanced analytical performance of chitosan-modified μPADs allowed the colorimetric detection of glucose in tear samples from four nondiabetic patients. The achieved concentration levels ranged from 130 to 380 μM. The modified μPADs offered analytical reliability and accuracy as well as no statistical difference from the values achieved through a reference method. Based on the presented results, the proposed μPAD can be a powerful alternative tool for non-invasive glucose analysis.

Highly sensitive colorimetric detection of glucose and uric acid in biological fluids using chitosan-modified paper microfluidic devices

Highly sensitive and selective cholesterol biosensor based on direct electron transfer of hemoglobin

Glucose oxidase (GOD) was encapsulated in chitosan matrix and immobilized on a glassy carbon electrode, achieving direct electron transfer (DET) reaction between GOD and electrode without any nano-material. On basis of such DET, a novel glucose biosensor was fabricated for direct bioelectrochemical sensing without any electron-mediator. GOD incorporated in chitosan films gave a pair of stable, well-defined, and quasireversible cyclic voltammetric peaks at about −0.284 (Epa) and −0.338 V (Epc) vs. Ag/AgCl electrode in phosphate buffers. And the peak is located at the potentials characteristic of FAD redox couples of the proteins. The electrochemical parameters, such as midpoint potential (E1/2) and apparent heterogeneous electron-transfer rate constants (ks) were estimated to −0.311 V and 1.79 s−1 by voltammetry, respectively. Experimental results indicate that the encapsulated GOD retains its catalytic activity for the oxidation of glucose. Such a GOD encapsulated chitosan based biosensor revealed a relatively rapid response time of less than 2 min, and a sufficient linear detection range for glucose concentration, from 0.60 to 2.80 mmol L−1 with a detection limit of 0.10 mmol L−1 and electrode sensitivity of 0.233 μA mmol−1. The relative standard deviation (RSD) is under 3.2% (n=7) for the determination of practical serum samples. The biologic compounds probably existed in the sample, such as ascorbic acid, uric acid, dopamine, and epinephrine, do not affect the determination of glucose. The proposed method is satisfactory to the determination of human serum samples compared with the routine hexokinase method. Both the unique electrical property and biocompatibility of chitosan enable the construction of a good bio-sensing platform for achieved DET of GOD and developed the third-generation glucose biosensors.

Unadulterated Glucose Biosensor Based on Direct Electron Transfer of Glucose Oxidase Encapsulated Chitosan Modified Glassy Carbon Electrode

A uric acid biosensor based on the direct electron transfer of a hemoglobin-encapsulated chitosan-modified glassy carbon electrode was developed for a highly sensitive and selective analysis in urine samples. The modified electrode was prepared by the encapsulation of hemoglobin and uricase in a chitosan matrix. The hydrogen peroxide produced from the catalytic oxidation of uric acid by uricase was reduced electrocatalytically by immobilized hemoglobin and used to obtain a sensitive amperometric response to uric acid. The linear response of the uric acid concentrations ranged from 2.00 to 30.0 μM with a correlation of 0.9982, the detection limit of uric acid was estimated to be 0.85 μM at a signal/noise ratio of 3. The uric acid biosensor can efficiently exclude the interference of commonly coexisted ascorbic acid, dopamine, epinephrine, etc. The relative standard deviation was under 2.56% (n = 5) for the determination of real samples. This biosensor is satisfactory for the determination of human urine samples compared with the HPLC-UV method.

Highly sensitive and selective uric acid biosensor based on direct electron transfer of hemoglobin-encapsulated chitosan-modified glassy carbon electrode.

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Highly sensitive and selective cholesterol biosensor based on direct electron transfer of hemoglobin

Unadulterated Glucose Biosensor Based on Direct Electron Transfer of Glucose Oxidase Encapsulated Chitosan Modified Glassy Carbon Electrode

Highly sensitive and selective uric acid biosensor based on direct electron transfer of hemoglobin-encapsulated chitosan-modified glassy carbon electrode.