The direct electrochemistry of glucose oxidase (GOD) adsorbed on a colloidal gold modified carbon paste electrode was investigated. The adsorbed GOD displayed a pair of redox peaks with a formal potential of-(4499±1) mV in 0.1M pH 5.0 phosphate buffer solution. The response showed a surface-controlled electrode process with an electron transfer rate constant of (38.99±5.3)/s determined in the scan rate range from 10 to 100mV/s. GOD adsorbed on gold colloid nanoparticles maintained its bioactivity and stability. The immobilized GOD could electrocatalyze the reduction of dissolved oxygen and resulted in a great increase of the reduction peak current. Upon the addition of glucose, the reduction peak current decreased, which could be used for glucose detection with a high sensitivity (8.4μA/mM), a linear range from 0.04 to 0.28mM and a detection limit of 0.01mM at a signal-to-noise ratio of 3σ. The sensor could exclude the interference of commonly coexisted uric and ascorbic acid.

A novel amperometric glucose sensor was constructed by immobilizing glucose oxidase (GOD) in a titania sol-gel film, which was prepared with a vapor deposition method. The sol-gel film was uniform, porous and showed a very low mass transport barrier and a regular dense distribution of GOD. Titania sol-gel matrix retained the native structure and activity of entrapped enzyme and prevented the cracking of conventional sol-gel glasses and the leaking of enzyme out of the film. With ferrocenium as a mediator the glucose sensor exhibited a fast response, a wide linear range from 0.07 to 15mM. It showed a good accuracy and high sensitivity as 7.2 μAcm-2 mM-1. The general interferences coexisted in blood except ascorbic acid did not affect glucose determination, and coating Nafion film on the sol-gel film could eliminate the interference from ascorbic acid. The serum glucose determination results obtained with a flow injection analysis (FIA) system showed an acceptable accuracy, a good reproducibility and stability and indicated the sensor could be used in FIA determination of glucose. The vapor deposition method could fabricate glucose sensor in batches with a very small amount of enzyme.

Sequence-known short-stranded hepatitis B virus (HBV) DNA fragment (181 bps) was obtained by PCR method. The strategy for its electrochemical detection was designed by covalently immobilizing single-stranded HBV DNA on gold electrode surface via carboxylate ester as a linkage between 3'-hydroxy end of DNA and carboxyl group of thioglycolic acid (TGA) self-assembled monolayer. The hybridization reaction on surface was evidenced by electrochemical methods using ferrocenium hexafluorophosphate (FcPF6) as an electroactive indicator. The interactions of Fc+with single-stranded (ss) and double-stranded (ds) HBV DNA immobilized on TGA monolayer were studied. The difference between the responses of Fc+at ss-and ds-DNA/Au electrodes suggested that this hybridization biosensor could be conveniently used to monitor DNA hybridization with a high sensitivity. AC impedance and XPS techniques have been employed to characterize the immobilization of ss-DNA on the gold surface.

The direct electrochemistry of hemoglobin (Hb) immobilized on a hexagonal mesoporous silica (HMS)-modified glassy carbon electrode was described. The interaction between Hb and the HMS was investigated using UV-Vis spectroscopy, FT-IR, and electrochemical methods. The direct electron transfer of the immobilized Hb exhibited two couples of redox peaks with the formal potentials of ?0.037 and ?0.232V in 0.1M (pH 7.0) PBS, respectively, which corresponded to its two immobilized states. The electrode reactions showed a surface-controlled process with a single proton transfer at the scan rate range from 20 to 200mV/s. The immobilized Hb retained its biological activity well and displayed an excellent response to the reduction of both hydrogen peroxide (H2O2) and nitrate (NO2-). Its apparent Michaelis-Menten constants for H2O2 and NO2-were 12.3 and 49.3μM, respectively, showing a good affinity. Based on the immobilization of Hb on the HMS and its direct electrochemistry, two novel biosensors for H2O2 and NO2-were presented. Under optimal conditions, the sensors could be used for the determination of H2O2 ranging from 0.4 to 6.0μM and NO2-ranging from 0.2 to 3.8μM. The detection limits were 1.86×10-9M and 6.11×10-7M at 3σ, respectively. HMS provided a good matrix for protein immobilization and biosensor preparation.

0.1 to 9.7 μmol dm-3 and a detection limit of 0.06 μmol dm-3 at 3σ. The amperometric determination of high concentrations of NO2-based on the irreversible reduction of NO could be performed at pH 4.0 with a linear range from 0.1 to 1.2 mmol dm-3. The surface of biosensor could be renewed quickly and reproducibly by a simple polish step. The biosensor has been used satisfactorily for nitrite determination in native water samples.