betadex and 3-3--5-5--tetramethylbenzidine

A novel Hg

Topics: Benzidines; beta-Cyclodextrins; Gold; Ions; Light; Limit of Detection; Mercury; Metal Nanoparticles; Oxidoreductases; Spectrophotometry; Temperature

This paper reports the use of a disposable voltammetric biosensor based on a screen-printed basal electrode and highly efficient mediators, the beta-cyclodextrin inclusion complexes tetramethylbenzidine and ferrocene. The polyphenol oxidase, contained in the crude extract of mushroom, was immobilized in the membrane of the cross-linked beta-cyclodextrin polymer. The resulting biosensor gave excellent analytical performance due to the supramolecular complexation for mediators. It responded to the concentration of dopamine with high selectively in the range from 1.0 x 10(-9) to 1.0 x 10(-6) M with a detection limit as low as 5 x 10(-10) M. The response time for reaching 90% of its steady-state value was less than 60 s, and the activity was retained for at least 15 days.

Topics: Agaricales; Benzidines; beta-Cyclodextrins; Biosensing Techniques; Catechol Oxidase; Cyclodextrins; Disposable Equipment; Dopamine; Electrodes; Enzymes, Immobilized; Equipment Design; Ferrous Compounds; Macromolecular Substances; Magnetic Resonance Spectroscopy; Metallocenes; Oxidation-Reduction; Patch-Clamp Techniques

This paper reports the results of UV-Vis spectrographic and electrochemical studying on the beta-cyclodextrin inclusion compound of 3,3',5,5'-tetramethylbenzidine (TMB). The molecules of TMB show better redox performance after they were included in the cavities of beta-cyclodextrin, especially while there were the redox enzyme. The composition of oxidization product in the inclusion compound is more single. The results were also revealed by the obviously increasing of voltammetrical current when this inclusion compound was modified on the electrode surface. It is reasonable to conclude that the formation of TMB-beta-cyclodextrin inclusion compound would enhance the sensitivity of those analytical methods based on the redox reaction of TMB.

Topics: Benzidines; beta-Cyclodextrins; Cyclodextrins; Electrochemistry; Oxidation-Reduction; Sensitivity and Specificity; Spectrophotometry, Ultraviolet

3,3',5,5'-Tetramethylbenzidine (TMB), a hydrophobic and noncarcinogenic chromogen with a high absorption coefficient widely used in solid-phase assays involving labeled horseradish peroxidase was rendered soluble (up to 40 mM) and more stable for at least 2 months at 22-24 degrees C by forming a water-soluble inclusion complex with 2-hydroxypropyl-beta-cyclodextrin (hp-beta-CyD). Cyclic voltammetry and absorbency measurement were employed to characterize the TMB-hp-beta-CyD complex. Well-defined cyclic voltammograms of TMB exhibited two oxidation waves which merged into a single wave with increasing hp-beta-CyD concentrations. Cyclic voltammetry was then used to examine the effect of complexation with hp-beta-CyD on the oxidation potential of TMB and provided evidence of a 1:1 complex between TMB and the cyclodextrin molecule with a formation constant of 1.6 M-1. Enzyme assays for D-glucose, lactate, and glutamate were performed by coupling the TMB-hp-beta-CyD/horseradish peroxidase system to the respective oxidase enzymes with the formation of either a blue (absorption coefficient of 35,800 M-1 cm-1 at 650 nm) or a yellow color (absorption coefficient of 67,300 M-1 cm-1 at 450 nm) as an indication of the metabolite concentration. These assays possessed a sensitivity limit below 10 microM and the results obtained were in excellent agreement with standard enzymatic assays when tested in various food and clinical samples.

Topics: 2-Hydroxypropyl-beta-cyclodextrin; Benzidines; beta-Cyclodextrins; Chromogenic Compounds; Cyclodextrins; Drug Stability; Electrochemistry; Glucose; Glutamic Acid; Horseradish Peroxidase; Hydrogen Peroxide; Hydrogen-Ion Concentration; Lactates; Lactic Acid; Solubility; Spectrophotometry; Water