Elaboration and characterization of spatially controlled assemblies of complementary polyphenol oxidase-alkaline phosphatase activities on electrodes.

The electrooxidation of a biotin pyrrole has allowed the formation of biotinylated polypyrrole films. Gravimetric measurements based on a quartz crystal microbalance demonstrate the efficient coupling of avidin, biotinylated polyphenol oxidase (PPO-B) and avidin-labeled alkaline phosphatase (AP-A) with the underlying biotinylated polymer film. The estimated mass increase corresponds to the anchoring of 1.6-1.8 equivalent layer of proteins. A step-by-step construction of bienzyme multilayers composed of PPO-B and AP-A was carried out on the electrode surface modified by the biotinylated polypyrrole film through avidin-biotin bridges. A spatially controlled distribution of the two enzymes was performed by the formation of one AP-A layer on 1, 5, and 10 PPO-B layers. The resulting bienzyme electrodes were applied to the determination of phenyl phosphate on the basis of amperometric detection of enzymically generated o-quinone at -0.2 V. Their analytical performances were analyzed in relation to the design of the enzyme architectures and in comparison with the amperometric behavior of the monoenzymatic electrodes (PPO-B electrode and AP-A electrode). It appears that at the 10-layer-PPO-B polypyrrole electrode only 4% of phenol is transformed, whereas 42-69% of phenyl phosphate is enzymatically consumed and detected at the AP-A polypyrrole electrode, depending on the enzyme activity. For the bienzymatic AP-A/PPO-B polypyrrole electrodes, the activity of each immobilized enzyme clearly affects the biosensor performance, the main limiting factor being the very low efficiency of PPO-B at pH 8.8.