The Sonogel-Carbon materials as basis for development of enzyme biosensors for phenols and polyphenols monitoring: a detailed comparative study of three immobilization matrixes.

Three amperometric biosensors based on immobilization of tyrosinase on a new Sonogel-Carbon electrode for detection of phenols and polyphenols are described. The electrode was prepared using high energy ultrasounds (HEU) directly applied to the precursors. The first biosensor was obtained by simple adsorption of the enzyme on the Sonogel-Carbon electrode. The second and the third ones, presenting sandwich configurations, were initially prepared by adsorption of the enzyme and then modification by mean of polymeric membrane such as polyethylene glycol for the second one, and the ion-exchanger Nafion in the case of the third biosensor. The optimal enzyme loading and polymer concentration, in the second layer, were found to be 285 U and 0.5%, respectively. All biosensors showed optimal activity at the following conditions: pH 7, -200 mV, and 0.02 mol l(-1) phosphate buffer. The response of the biosensors toward five simple phenols derivatives and two polyphenols were investigated. It was found that the three developed tyrosinase Sonogel-Carbon based biosensors are in satisfactory competitiveness for phenolic compounds determination with other tyrosinase based biosensors reported in the literature. The detection limit, sensitivity, and the apparent Michaelis-Menten constant K(m)(app) for the Nafion modified biosensor were, respectively, 0.064, 0.096, and 0.03 micromol, 82.5, 63.4, and 194 nA micromol(-1)l(-1), and 67.1, 54.6, and 12.1 micromol l(-1) for catechol, phenol, and 4-chloro-3-methylphenol. Hill coefficient values (around 1 for all cases), demonstrated that the immobilization method does not affect the nature of the enzyme and confirms the biocompatibility of the Sonogel-Carbon with the bioprobe. An exploratory application to real samples such as beers, river waters and tannery wastewaters showed the ability of the developed Nafion/tyrosinase/Sonogel-Carbon biosensor to retain its stable and reproducible response.