Carbon Nanotubes and Algal Polysaccharides To Enhance the Enzymatic Properties of Urease in Lipid Langmuir-Blodgett Films.

Algal polysaccharides (extracellular polysaccharides) and carbon nanotubes (CNTs) were adsorbed on dioctadecyldimethylammonium bromide Langmuir monolayers to serve as a matrix for the incorporation of urease. The physicochemical properties of the supramolecular system as a monolayer at the air-water interface were investigated by surface pressure-area isotherms, surface potential-area isotherms, interfacial shear rheology, vibrational spectroscopy, and Brewster angle microscopy. The floating monolayers were transferred to hydrophilic solid supports, quartz, mica, or capacitive electrolyte-insulator-semiconductor (EIS) devices, through the Langmuir-Blodgett (LB) technique, forming mixed films, which were investigated by quartz crystal microbalance, fluorescence spectroscopy, and field emission gun scanning electron microscopy. The enzyme activity was studied with UV-vis spectroscopy, and the feasibility of the thin film as a urea sensor was essayed in an EIS sensor device. The presence of CNT in the enzyme-lipid LB film not only tuned the catalytic activity of urease but also helped to conserve its enzyme activity. Viability as a urease 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 are related to the synergism between the compounds on the active layer, leading to a surface morphology that allowed fast analyte diffusion owing to an adequate molecular accommodation, which also preserved the urease activity. This work demonstrates the feasibility of employing LB films composed of lipids, CNT, algal polysaccharides, and enzymes as EIS devices for biosensing applications.

Structural and viscoelastic properties of floating monolayers of a pectinolytic enzyme and their influence on the catalytic properties.

HYPOTHESIS: The catalytic activity of enzymes immobilized in self-assembly systems as Langmuir-Blodgett (LB) films is influenced by molecular interactions dictated by the composition and viscoelasticity of the previous floating monolayers. We believe that the insertion of carbon nanotubes (CNT) in mixed polygalacturonase/lipid monolayers may influence intermolecular interactions and viscoelastic properties, being then possible to tune system stability and rheological properties, driving catalytic properties of the films for biosensing. EXPERIMENTS: The physicochemical properties of the monolayers were investigated by tensiometry, surface potential, Brewster angle microscopy, infrared spectroscopy, and dilatational rheology. The monolayers were transferred to solid supports LB films and characterized by atomic force microscopy, quartz crystal microbalance, and fluorescence spectroscopy. The catalytic activity of the LB films was verified by colorimetric assay. FINDINGS: The enzyme-CNT-lipid film had a catalytic activity at least twice as high as the pure enzyme owing to the synergy between the components, with the lipid acting as a protector matrix for the enzyme and the CNTs acting as an energy transfer facilitator. These results point to a proof-of-concept system, through which we can propose an alternative to achieve enhanced bio-inspired films with high control of the molecular architecture by using the LB approach.