Abstract

In this study, glucose oxidase was used as stabilization medium due to its higher efficiency, ability for more accurate control of enzyme reaction, protecting against wasting of enzyme as well as simple and easy use and exchange of enzyme medium after performing some levels of surface modification and developing single–walled carbon nanotubes (SWCNT) on gold plates. For better connecting and stabilizing of the enzyme on the medium, the prepared medium was washed with concentrated sulfuric acid and nitric acid and a large volume of deionized water. For protecting the enzyme from devastating effects of gold and prohibiting it from becoming inactive, the surface was covered with cystamine before stabilization. Regarding the large size of glucose oxidase compared to the surface of the medium, a connective material with amid at one end and pyrine at the other end was used as a transfer agent, and for stabilizing this connection the prepared medium was placed into dimethylformamide (DMF) solution for a couple of hours. Activity of the stabilized enzyme at the wavelength of 460 nm recorded by spectroscope was depicted against time to evaluate its stability at various times. The prepared medium, which had a large amount of glucose oxidase, could be used as an electrode in sensors. Furthermore, glucose oxidase electrochemical sensor is one of the best methods for detecting low amounts of glucose, and applying gold colloidal nanoparticles as a supplementary material in the structure of biosensors can be effective for improving its efficiency and optimum performance. In this study, a modified carbon paste electrode biosensor with gold colloidal nanoparticles (A_unano/CPE) was produced by carbon graphite powder, paraffin oil and, gold colloidal nanoparticles (24 nm), and was compared with carbon paste electrode (CP). In semi–permeable membranes, a combination of 1 ml of 0.1 M phosphate buffer with specified pH and 10 mg of glucose oxidase was placed around each electrode. At the same potential of 0.7 V, biosensors were tested with glucose in the concentration range of 0–1 mM and various pH (4, 6, and 8), which led to the production of the maximum current and tracing glucose at pH=6 and concentration of 1 M as the optimum condition. Currentmetry induced from both biosensors was compared and confirmed that using gold colloidal nanoparticles in the structure of A_unano/CPE electrode led to the increase of the conductivity and currentmerty of the biosensors. Qualitative and quantitative measurement of food components is of great importance due to high cost of traditional methods, in addition to tendency for more accurate and sensitive detecting of these components. Glucose and cholesterol are such compounds that are frequently measured. Various methods are used to detect these food elements, however the necessity for accurate measurement of these two compounds with high sensitivity, especially for food health issues, leads to the development of biological methods, especially biosensors. Among them, biosensors based on conductive polymer nanostructures, especially polyaniline, have been recently gained interest due to their unique characteristics. The current paper aims to introduce and investigate the previously performed studies about polyaniline–based biosensors for detecting glucose and cholesterol.