Langmuir and Langmuir-Blodgett films of lipids and penicillinase: Studies on adsorption and enzymatic activity

Bioelectronic devices, such as biosensors, can be constructed with enzymes immobilized in ultrathin solid films, for which preserving the enzymatic catalytic activity is fundamental for optimal performance. In this sense, nanostructured films in which molecular architectures can be controlled are of interest. In this present work, the adsorption of the enzyme penicillinase onto Langmuir monolayers of the phospholipid dimyristoylphosphatidic acid was investigated and characterized with surface pressure-area isotherms and polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS). The incorporation of the enzyme in the lipid monolayer not only caused the film to expand, but also could be identified through amide bands in the PM-IRRAS spectra, with the C-N and C=O dipole moments being identified, lying parallel to monolayer plane. Structuring of the enzyme into a-helices was identified in the mixed enzyme-phospholipid monolayer and preserved when transferred to solid as a Langmuir-Blodgett (LB) film. The enzyme-lipid LB films were then characterized with PM-IRRAS, atomic force microscopy and fluorescence spectroscopy. Measurements of the catalytic activity showed that the enzyme accommodated in the LB films preserved 76% of the enzyme activity in relation to the homogeneous medium. The method presented here not only allows for enhanced catalytic activity toward penicillin, but also can be useful to explain why certain film architectures exhibit better enzyme activity. (C) 2014 Elsevier B.V. All rights reserved.