Hybrid Film Biosensor for Phenolic Compounds Detection

Phenolic compounds are industrial chemicals widely used in the manufacture of products. Most of them are generated artificially and are found in the wastewaters from chemical plants, exhaust gases from incinerators, the side stream smoke from cigarettes. They are easily adsorbed in humans, regardless of their form. High levels of phenols have been shown to have detrimental effects on animal health, and some phenolic compounds are reportedly carcinogenic (N. Li et al., 2005) and allergenic (Haghighi et al., 2003), and due to their toxic effects, their determination and removal in the environment are of great importance. Biosensors can make ideal sensing systems to monitor the effects of pollution on the environment, due to their biological base, ability to operate in complex matrices, short response time and small size. The determination of phenol and its derivative compounds is of the environmental greatness, since these species are released into the environment by a large number of industries, e.g. the manufacture of plastics, dyes, drugs, antioxidants and waste waters from pulp and paper production. This group of biosensors is of great interest because of their application in food and pharmaceutical industry. Among enzymes, laccases and tyrosinases (Duran et al., 2002) or horse-radish peroxidase (Freire et al., 2001) as well as polyphenol oxidase are groups of enzymes that catalyze the transformation of a large number of phenolic compounds. The mechanism for tyrosinase, laccase and peroxidase in the electrochemical biosensors are different. Enzyme molecules are re-reduced by phenolic compounds after they were oxidized by oxygen (for tyrosinase and laccase) or hydrogen peroxide (for peroxidase) on the surface to the electrode. The tyrosinase biosensors are applicable to the monitoring of phenolic compounds with at least one free ortho-position. On the other hand, the laccase biosensor can detect phenolic compounds with free paraand methaposition with a complicated catalytic cycle. Horseradish peroxidase (HrP) based biosensors are most sensitive for a great number of phenolic compounds since phenols can be act as electron donors for peroxidase (Yang et al., 2006). As seen, phenolooxidases have wide substrate specificity and a great potential for the determination of phenolic compounds. Furthermore, fungal laccases catalyze demethylation reactions an important and initial step of the biodegradation process of the lignin polymer