ИСТИНА

Organized multilayered polymer thin films can be constructed via alternative adsorption of polyelectrolytes. The adsorption of each new layer is to a great extent determined by the state and structure of pre-adsorbed polymer layers. The same rule apparently works when polyelectrolyte-mediated adsorption of enzymes is used for their immobilization, specifically, for a design and fabrication of bioanalytical devices, e.g., biosensors. The amount of an enzyme incorporated and the strength of its binding have the most important influence on basic characteristics, such as activity and operation stability, of these bioanalytical surfaces. The interaction of star-like micelles of an ionic amphiphilic diblock copolymer with a polycationic block, polybutadiene-block-poly(2-(dimethylamino)ethyl methacrylate), PB250-b-PDMAEMA507 with a graphite surface was studied (subscripts denote number-average degrees of polymerization). The adsorption of two enzymes, tyrosinase (Tyr) and choline oxidase (ChO) on the graphite surface modified with this diblock copolymer was also investigated. Finally, the polymer/enzyme bilayers were tested as biosensors for choline and phenol for their activity and stability and compared to already existing setups. PB250-b-PDMAEMA507 micelles adsorbed onto a graphite surface underwent pH-induced changes of their supramolecular structure at pH > 7.0. This results in a more homogeneous coverage of the graphite surface by the diblock copolymer. Therefore, the resulting polymer film can potentially bind more enzyme molecules. This inference is proven by measurements of the enzymatic activities of PB250-b-PDMAEMA507/Tyr and PB250-b-PDMAEMA507/ChO films as a function of pH of polymer solution used at the stage of polymer deposition. A pronounced increase in the enzymatic activities of both tyrosinase and choline oxidase for phenol and choline detection, respectively, was observed with the increasing pH of deposition of PB250-b-PDMAEMA507 micelles from 2.0 to 10.0. Thus, the use of the block copolymer micelles as a component for biosensor coatings allow to achieve more than a 3-fold increase in biosensor sensitivity in a comparison with biosensor coating formed from the same enzymes and corresponding linear homopolyelectrolytes. Additionally, the operation stability of biosensor coatings based on diblock copolymer micelles improves by a factor of ca. three as compared to that of coatings based on the corresponding linear homopolyelectrolytes. These results demonstrate a high potential for the use of micelle-forming diblock copolymers for the construction of polymer-enzyme coatings for biosensors with improved enzymatic activities and enhanced operation stability.