Layered nanoarchitectures between cationic and anionic materials - Composite assemblies of polyions, lipid bilayers, and proteins

Many functional molecules such as polyions, proteins, colloidal particles, dyes, and lipid membranes, can be assembled as thin films through layer-by- layer alternate adsorption. This technique is useful for preparing nano-siz ed enzyme reactors where the enzymes are sandwiched between molecular films of polyions or lipids. In order to systematically compare the enzymatic ac tivity and the related properties between the polyion-protein assemblies an d lipid-protein assemblies, in this study, we prepared both kinds of assemb lies and examined their enzymatic activity. Two kinds of enzymes, lactate d ehydrogenase (LDH) and alcohol dehydrogenase (ADH), were assembled with the polycation, poly(diallyldimethylammonium chloride) (PDDA), and an artifici al cationic lipid. The assembling behavior was analyzed by a quartz crystal microbalance (QCM) with nanogram precision which revealed that the polyion , the lipid membrane, and the enzyme layers can be repeatedly and reproduci bly assembled. The catalytic activity of the obtained films was spectrophot ometrically examined. The activity of the LDH on a lipid-surface film was a pparently greater than that of the LDH on a polyion-surface film. This diff erence might originate from the difference in the surface nature of the fil ms. The Michaelis-Menten analysis suggested that the concentration increase in an anionic substrate in the vicinity of the cationic lipid surface led to the enhanced enzymatic activity. The surface morphology of the film was investigated using atomic force microscopy(AFM). The lipid-surface film app arently has a rough surface, while a relatively smooth surface morphology w as observed for the polyion-surface film. This difference in the surface mo rphology might affect the activity of the immobilized enzymes.