Phenol-sensitive enzyme electrode with substrate cycling for quantification of certain inhibitory aromatic acids and thio compounds

Abstract

A Clark oxygen electrode coated with a membrane of crosslinked champignon phenol oxidase (tyrosinase)is able to detect phenol containing analytical samples 3-5 times more sensitively after the admixture of hydrazine hydrochloride to the reaction buffer. This compound will recycle the substrate via chemical reduction of the quinoid product thus simultaneously preventing the membrane from rapid blackening. The decrease of oxygen in the membrane due to phenol oxidation is rapidly compensated by diffusion from the bulk solution when an inhibitor of the membrane-bound phenol oxidase is added to the reaction medium. This effect has been utilized for the measurement of low concentrations of compounds decreasing the sensitivity of the bioelectrode either reversibly (benzoic acid, 3- and 4-aminobenzoic acid, salicylic acid, 4-aminosalicylic acid, nicotinic acid, 4-nitrophenol, 1-naphthol) or irreversibly (phenylthiourea, thioacetamide, L-cysteine, reduced glutathione, 2-mercaptoethanol, 2,3-dimercaptopropanol and others). Benzoate as a potent reversible inhibitor markedly stabilizes the phenol oxidase reaction membrane during its storage either in the buffer or in dry state at 4 °C for one year at least.

Magnetic Nanoparticles Modified with Carbon Nanotubes for Electrocatalytic Magnetoswitchable Biosensing Applications

“…It is possible that the formation of such compounds might have inactivated the enzyme and fouled the electrode, which would alter the overvoltage and the electron transfer rate. This might then have affected the mass transportation of electroactive species to the electrode surface, [ 29,30 ] which would affect the electrochemical signal of o -quinone produced from the enzymatic reaction. However, comparing the anodic ( I pa = + 11.19 μ A) and cathodic ( I pc = + 11.92 μ A) peak currents of SPE/MNP-Tyr (curve b) and SPE/MNP-Tyr-MWCNT (curve c), both functionalized with tyrosinase, a higher current intensity was found for SPE/MNP-Tyr-MWCNT (curve c) with different anodic and cathodic peak currents of + 4.31 μ A and + 2.65 μ A, respectively.…”

Biosensing of rapeseed glucosinolates using amperometric enzyme electrodes based on membrane‐bound glucose oxidase or tyrosinase

“…The whole plant body contained 20.6pmol and 19.7pmol of total glucosinolates per gram of dry weight when analyzed with the glucose oxidase and the tyrosinase membrane sensor, respectively. A full scheme of sample processing and electroanalysis is as follows The negligible change of the background current measured with a tyrosinase bioelectrode prior to treatment of the rapeseed extract with myrosinase and ammonia shows that some potential interferents (inhibitory aromatic acids, cysteine, reduced glutatione [9]) have to occur below the detection limit.…”

“…The measuring cell equipped with the tyrosinase membrane biosensor was filled with 3.0mL 0.1 M phosphate buffer at pH 7.0 containing 5 mM hydrazine hydrochloride [9]. When the background current had stabilized, a small volume of 0.1 M catechol was added to reach the current decrease corresponding to about 70 % drop of the oxygen level (25-30 % of the full scale deflection).…”

Enzymatic substrate recycling electrodes

“…With intermittent PQQ incubations the electrodes could be used for more than 4 weeks. Substituting the electrode by a reducing agent may also improve sensitivity due to a regeneration process (Macholan, 1990;Uchiyama et aI., 1993). For example, the addition of ascorbic acid to a phenol oxidase modified electrode improves the sensitivity by a factor of 300 (Uchiyama et aI., 1993).…”