A Novel Cholesterol Oxidase Biosensor Based on Pt-nanoparticle/Carbon Nanotube Modified Electrode

A Pt-nanooarticle/carbon nanotube modified graphite electrode immobilized with cholesterol oxidase/sol＇-gel layer was developed for monitoring cholesterol.Using this electrode,cholesterol concentration（4.0×10^-6 tp 1.0×10^-4mol/L）could be determined accurately in the presence of ascorbic or uric acid,and the response time was rapid （〈 20 s）. This biosensor has high sensitivity and selectivity.

Self-assembly of metal-cholesterol oxidase hybrid nanostructures and application in bioconversion of steroids derivatives

A cholesterol oxidase(COD)was hybridized with Ca^(2+),Zn^(2+),Al^(3+),Fe^(2+) and Mn^(2+).After precipitation with PO_(4)^(3-) at 4℃ for 72 h,the resulting pellets were freeze-dried.In scanning electron microscopy assays,the metal-COD complexes revealed flower-like or granular structures after hybridization.Fourier transform infrared spectroscopy assay revealed the characteristic peaks of both the enzyme and metal materials.X-ray diffraction analysis indicated that COD was encapsulated in CaHPO_(4)·2H_(2)O-,Zn_(3)(PO_(4))_(2)·4H_(2)O-,AlPO_(4-),FeP_(4-) and Mn_(3)(PO_(4))_(2)·3H_(2)O-based nanostructures,respectively.Differential scanning calorimetry assay indicated significant increases in thermo-denaturation temperatures from 60.5℃ to 167.02℃,167.02℃,137.70℃,172.85℃ and 160.99℃,respectively.Using steroid derivatives as substrates,this enzyme could convert cholesterol,pregnenolone,dehydroepiandrosterone,ergosterol,b-sitosterol and stigmasterol to related single products.Hybridization in metal-based nanostructures could significantly enhance the initial conversion ratio and reaction stability of the enzyme.In addition,substrate selectivity could be affected by various metal materials.Briefly,using Ca^(2+),Zn^(2+),Al^(3+),Fe^(2+) and Mn^(2+) as hybrid raw materials could help to encapsulate COD in related metal-enzyme nanostructures,and could help to promote the stability and tolerant properties of the enzyme,while also enhancing its catalytic characteristics.

Cholesterol oxidase biosensor based on a glassy carbon electrode modified with Nafion and methyl viologen

Cholesterol oxidase biosensor has been constructed by using bovine serum albumin and glutaraldehyde as cross linker to immobilize cholesterol oxidase and cholesterol esterase on a glassy carbon electrode modified with Nafion and methyl viologen. The biosensor has been used to determine total cholesterol in blood. The linear range of the determination is 2.5×10to 1.0×10-4 mol/L. The detection limit is about 5.0×10mol/L. The response time is 12 s. This biosensor has the advantage of high selectivity, sensitivity and short response time.

Polydimethylsiloxane Microchip Capillary Electrophoresis for Determination of Cholesterol

Microchip capillary electrophoresis （MCE） has significant impact on diagnostic testing. One of the most importance in clinical analysis test is the determination of cholesterol level in blood, because its increase is associated with coronary heart disease which is a major cause of death world over. Polydimethylsiloxane （PDMS） was material used to make a MCE for determination of cholesterol. Hydrogen peroxide was generated from the oxidation of cholesterol with cholesterol oxidase （ChOx） and was detected electrochemically at a downstream gold （Au） wire electrode by amperometry. Various parameters, such as the detection potential, concentration of running buffer, pH of running buffer, separation voltage, injection time, and concentration of ChOx, were studied. The migration time of cholesterol is less than 100s and the calibration curve is linear from 50 mg.dL-1 to 250 mg-dL-1 with the coefficient of determination （R2） of 0.9955. Therefore, this proposed assay is very rapid and sensitive for the detection of cholesterol.

Polyaniline/Prussian Blue Composite Film Electrochemical Biosensors for Cholesterol Detection

An electrochemical biosensor fabricated by immobilization of cholesterol oxidase (ChOx) in a polyaniline (PAN)/prussian blue (PB) conductive layer of glassy carbon electrode has been prepared, based on the detection of hydrogen peroxide produced by ChOx at -0.05 V. The properties of the biosensor were investigated and the measurement conditions for cholesterol were optimized. A linear relationship between electrochemical signal and cholesterol concentration in a range of 1×10 -6-8×10 -5 mol/L was observed. It is one of the most sensitive sensors for cholesterol determination, since a low detection limit of 1.8×10 -7 mol/L was found. Good properties of the biosensor were attributed to high activity of ChOx and effective electro-catalysis of PB modifier in the composite layer on electrode surface.

Gold nanoparticles/single-stranded DNA-reduced graphene oxide nanocomposites based electrochemical biosensor for highly sensitive detection of cholesterol

High density and uniform distribution of the gold nanoparticles functionalized single-stranded DNA modified reduced graphene oxide nanocomposites were obtained by non-covalent interaction.The positive gold nanoparticles prepared by phase inversion method exhibited good dimensional homogeneity and dispersibility,which could readily combine with single-stranded DNA modified reduced graphene oxide nanocomposites by electrostatic interactions.The modification of single-stranded DNA endowed the reduced graphene oxide with favorable biocompatibility and provided the preferable surface with negative charge for further assembling of gold nanoparticles to obtain gold nanoparticles/single-stranded DNA modified reduced graphene oxide nanocomposites with better conductivity,larger specific surface area,biocompatibility and electrocatalytic characteristics.The as-prepared nanocomposites were applied as substrates for the construction of cholesterol oxidase modified electrode and well realized the direct electron transfer between the enzyme and electrode.The modified gold nanoparticles could further catalyze the products of cholesterol oxidation catalyzed by cholesterol oxidase,which was beneficial to the enzyme-catalyzed reaction.The as-fabricated bioelectrode exhibited excellent electrocatalytic performance for the cholesterol with a linear range of 7.5–280.5μmol·L^(−1),a low detection limit of 2.1μmol·L^(−1),good stability and reproducibility.Moreover,the electrochemical biosensor showed good selectivity and acceptable accuracy for the detection of cholesterol in human serum samples.