Graphene Oxide Modulating the Bioelectronic Properties of Penicillinase Immobilized in Lipid Langmuir-Blodgett Films.

In this paper, graphene oxide was incorporated in penicillinase-lipid Langmuir monolayers and transferred to solid supports as Langmuir-Blodgett (LB) films so that the enzyme catalytic properties could be evaluated. Adsorption of penicillinase and graphene oxide on dimyristoylphosphatidic acid (DMPA) monolayers at the air-water interface was investigated by tensiometry, vibrational spectroscopy, and Brewster angle microscopy. The LB films were characterized by quartz crystal microbalance, infrared spectroscopy, luminescence spectroscopy, and atomic force microscopy. Enzyme activity was studied with UV-vis spectroscopy, and the feasibility of the supramolecular device nanostructured as ultrathin films was essayed as an optical sensor device. The presence of graphene oxide in the enzyme-lipid LB film not only tuned the catalytic activity of penicillinase but also helped conserve its enzyme activity after weeks. These results may be related not only to the molecular architecture provided by the film but also to the synergism between the compounds on the active layer, leading to a molecular architecture that allowed a fast analyte diffusion owing to a suitable molecular accommodation which also preserved the penicillinase activity. This work then demonstrates the feasibility of employing LB films composed of lipids, graphene oxide, and enzymes as optical devices for biosensing applications as a proof-of-concept experiment.

Carbon Nanotubes Arranged As Smart Interfaces in Lipid Langmuir-Blodgett Films Enhancing the Enzymatic Properties of Penicillinase for Biosensing Applications.

In this paper, carbon nanotubes (CNTs) were incorporated in penicillinase-phospholipid Langmuir and Langmuir-Blodgett (LB) films to enhance the enzyme catalytic properties. Adsorption of the penicillinase and CNTs at dimyristoylphosphatidic acid (DMPA) monolayers at the air-water interface was investigated by surface pressure-area isotherms, vibrational spectroscopy, and Brewster angle microscopy. The floating monolayers were transferred to solid supports through the LB technique, forming mixed DMPA-CNTs-PEN films, which were investigated by quartz crystal microbalance, vibrational spectroscopy, and atomic force microscopy. Enzyme activity was studied with UV-vis spectroscopy and the feasibility of the supramolecular device nanostructured as ultrathin films were essayed in a capacitive electrolyte-insulator-semiconductor (EIS) sensor device. The presence of CNTs in the enzyme-lipid LB film not only tuned the catalytic activity of penicillinase but also helped conserve its enzyme activity after weeks, showing increased values of activity. Viability as penicillin sensor was demonstrated with capacitance/voltage and constant capacitance measurements, exhibiting regular and distinctive output signals over all concentrations used in this work. These results may be related not only to the nanostructured system provided by the film, but also to the synergism between the compounds on the active layer, leading to a surface morphology that allowed a fast analyte diffusion because of an adequate molecular accommodation, which also preserved the penicillinase activity. This work therefore demonstrates the feasibility of employing LB films composed of lipids, CNTs, and enzymes as EIS devices for biosensing applications.