PULSED-LASER METAL CONTACTING OF BIOSENSORS ON THE BASIS OF CRYSTALLINE ENZYME-PROTEIN LAYER COMPOSITES

Crystalline bacterial cell surface layers (S-layers) composed of monom olecular arrays of protein subunits are accessible to a wide variety o f possible proteinchemical reactions. This enables the attachment and immobilization of enzyme molecules in a tightest packing, which has no t been achieved with other immobilization matrices. When immobilized t o an S-layer lattice, the enzyme entities are surrounded by nanometer pores. Thus, they can react electrochemically with the analyte liquid streaming through these pores. The control over this process has to ta ke place by way of an inert electrical contact in a distance of less t han 1 nm. The relatively voluminous, but specially shaped sensor enzym e molecules have to be connected with an optimum metallic contact, whi ch must not disturb the protein structure. Previously, platinum films were applied on enzyme layers immobilized on S-layer protein by argon sputtering. This conventional technique, however, exhibits substantial limitations. One, for instance, is the volume change of the S-layer/e nzyme composite system when it is introduced into a conventional vacuu m coating apparatus. This coating problem can be circumvented by a com pletely new deposition method, i.e. the pulse-laser-deposition (PLD) o n protein crystal composite films with optimized laser parameters and reaction atmospheres. Enzyme activities of 70-80% were achieved, thus demonstrating that composite systems consisting of the 2D-protein-laye r/enzyme/metal sequence can successfully serve as highly efficient sen sor systems. (C) 1997 Elsevier Science S.A.