Enzyme Multilayer-Modified Porous Membranes as Biocatalysts

Abstract

Porous polycarbonate (PC) membranes with pore diameters of either 400 or 100 nm were used as supports for the layer-by-layer deposition of peroxidase−poly(sodium 4-styrenesulfonate) complexes [(POD−PSS)c] and oppositely charged poly(allylamine hydrochloride) (PAH) to prepare high-surface-area thin films for biocatalysis. Formation of the multilayer films was verified by scanning electron microscopy and transmission electron microscopy following dissolution of the porous PC template to generate POD/polyelectrolyte (PE) tubes. An average thickness of ∼5 nm was calculated for each (POD−PSS)c/PAH bilayer, as determined from microscopy images. The activity of the POD/PE multilayer films was found to be dependent on the amount of enzyme in the film (which is determined by the number of (POD−PSS)c layers deposited) and the total membrane surface area. Films deposited on the PC membranes with 100-nm-diameter pores showed maximum bioactivity at five (POD−PSS)c layers. Beyond this layer number the total membrane activity decreased sharply, which is attributed to membrane pore blockage. Films deposited on PC membranes with pore diameters of 400 nm showed regularly increasing bioactivity up to seven (POD−PSS)c layers, with a plateau in activity observed thereafter. Activity enhancements of up to almost an order of magnitude larger were observed for the enzyme films deposited on the PC membranes (e.g., 100-nm pore diameter membranes with 4% porosity), compared with identical films formed on nonporous supports (e.g., quartz slides) with the same geometrical area. The reported method for the preparation of membrane-supported biocatalysts provides a viable approach for the generation of high-enzyme-content thin films with tailored bioactivity.