A conductometric tyrosinase biosensor has been developed to determine herbicides, alachlor, diazinon and carbaryl, in aqueous solutions. Tyrosinase from mushroom was immobilized on the sensitive part of interdigitated platinum planar electrodes by cross-linking with bovine serum albumin (BSA) in saturated glutaraldehyde (GA) vapor for 30 min. Herbicides inhibited tyrosinase, and the decrease of enzyme activity was used to determine these herbicides. Parameters influencing the performance of the systems were optimized to be used in the inhibition procedures. Detection limits for diazinon, alachlor and carbaryl were about 5.0×10-8, 1.5×10-7 and 2.0×10-7 M, respectively. A relative standard deviation (RSD) (five times successive measurements) of the conductance responses is 5%. The 90% of the enzyme activity was still maintained after four weeks of storage at 4 oC in 5.0 mM phosphate buffer, pH 7.0.
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