The Fabrication And Application Of Electrochemical Enzyme Sensors Based On Ionic Liquids And Gold Nanoparticles

There are considerable attention focused on the enzyme sensors due to the broadapplications prospects in analytical task such as biological analysis, quality control offood, clinical diagnosis, etc. Recently, the rapid development of biomaterials andnanomaterial, has caused a remarkable innovation in the design and construction ofenzyme sensors. In the design of enzyme sensors, how to immobilize thebiomolecules stably and high activity based on the advantages of the nanomaterialsbecame the crucial problem. We prepared several types of nanomaterials by differentstrategy and applied them into the construction of the enzyme sensors. The maincontents are summarized as follows:1.A novel cholesterol biosensor was fabricated on hydrophobic ionic liquid （IL）/aqueous solution interface. The hydrophobic IL thin film played a signal amplificationrole because it not only enriched the cholesterol from the aqueous solution, but alsoimmobilized matrix for Cholesterol oxidase （ChOx）. Prussian Blue （PB） as advancedsensing materials was used as effective low-potential electron transfer mediationtoward hydrogen peroxide （H₂O₂）.The fabricated IL-ChOx/PB/Glassy carbonelectrode （GCE） was characterized by electrochemical impedance spectroscopy （EIS）and cyclic voltammogram （CV）, respectively. And it exhibited a linear response tocholesterol in the range of0.01–0.40mM with a detection limit of4.4μM. Inaddition, the kinetics behavior of cholesterol at IL-Chox/PB/GCE electrode wasexamined, and the electrocatalytic mechanism was proposed. ChOx immobilized inhydrophobic IL thin film was used as the first electrocatalyst for the cholesterol intoH₂O₂, and the PB film onto the GCE was used as the second electrocatalyst for the2e-reduction of the produced H₂O₂into H₂O.2.We presented a novel Au nanoparticles （AuNPs） covalent modified strategy,and established a direct electron transfer （DET） pathway between the AuNPs modifiedglassy carbon electrode and the enzyme redox active centre. This pathway consistedof covalent Au-C bond and charged p-aminophenyl or p-carboxyphenyl groups.Firstly, AuNPs were electrodeposited on the top of glassy carbon electrode, then modified with aryl diazonium salts generated in situ from p-aminobenzoic acid（PABA） or p-phenylenediamine （PPD）. The two charged-type modified electrodes:NH₂-Ph-AuNPs/GCE and COOH-Ph-AuNPs/GCE were achieved. Next，the twomodified electrodes were characterized by the combined used of electrochemicalmeasurement, surface enhancement Raman spectroscopy （SERS）, X-rayphotoelectron spectroscopy （XPS） and field emission scanning electron microscopy（FESEM）. Secondly, the very efficient DET currents were produced betweenCytochrome c （Cyt c） and NH2-Ph-AuNPs/GCE negatively surface, horseradishperoxidase （HRP） and COOH-Ph-AuNPs/GCE positively surface. Finally, the kineticsbehaviors of Cyt c and HRP at the two type electrodes were also comparativeinvestigated.3.Highly stable and hydrophobic ionic liquid-capped gold nanoparticles werefirstly syntheized by reduction of HAuCl4in situ in the two-phase system. theprepared hydrophobic ionic liquid-capped gold nanoparticles colloidal solution werecharacterized by UV-vis spectra, transmission electron microscopy（TEM）. Then weused the syntheized material as the matrix for immbolizing the cholesterol oxidase tofabricate the cholesterol biosensors. Cyclic voltammetry and amperometry were usedto characterize the biosensors performances. The sensors exhibited wide linear rangesand low detection limits,thus demonstrating their potential for use in cholesterolanalysis.