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A screen-printed four-electrode sensor based on immobilization of laccase (Coriolus hirsutus), peroxidase (horseradish) and tyrosinase (mushroom) in the same array was developed for monitoring of phenols. The enzymes were immobilized onto a self-assembled monolayer (4-mercapto-1-butanol) modified gold surface via covalent attachment by epichlorohydrin coupling. The experimental conditions for simultaneous operation of the three enzymes were optimized based on catechol determination. The sensors were further applied for the amperometric detection of several substituted phenolic compounds, carried out using a single line flow-injection system. Hydrogen peroxide served as co-substrate for peroxidase. The limits of detection for phenols in aqueous solutions were in the micromolar range, one assay was completed in less than 5 min. The preliminary studies showed that the compatibility of the above mentioned enzyme array enabled the multielectrode biosensor to be applied to real samples including industrial wastewaters and surface waters.

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Screen-printing technology for electrode fabrication enables construction of amperometric devices suitable for combination of several enzyme electrodes. To develop a biosensor array for characterisation of wastewaters, tyrosinase and horseradish peroxidase (HRP) or cholinesterase-modified electrodes were combined on the same array. The behaviour of the tyrosinase-modified electrode in the presence of hydrogen peroxide (required co-substrate for the HRP-modified electrode) and acetylthiocholine chloride (required co-substrate for cholinesterase) was studied. Performance of bi-enzyme biosensor arrays in the batch mode and in the flow-injection system are discussed.