Acylated Carrageenan Changes the Physicochemical Properties of Mixed Enzyme–Lipid Ultrathin Films and Enhances the Catalytic Properties of Sucrose Phosphorylase Nanostructured as Smart Surfaces

Insertion of carbon nanotubes in Langmuir-Blodgett films of stearic acid and asparaginase enhancing the catalytic performance

In this paper, carbon nanotubes (CNT) were adsorbed on stearic acid (SA) Langmuir monolayers to serve as matrices for the incorporation of asparaginase. The interaction between the components at the air-water interface was evaluated by surface pressure-area isotherms, surface potential-area isotherms, polarization-modulation reflection absorption infrared spectroscopy (PM-IRRAS), and Brewster angle microscopy (BAM). The enzyme expanded the monolayers and changed the thermodynamic and electrical properties of the SA-CNT monolayers, as detected with the isotherms. PM-IRRAS spectra showed that the enzyme keeps its secondary structure when adsorbed at the monolayers and also alters the morphology of the air-water interface, as identified with BAM. The hybrid floating films were transferred to solid supports through the Langmuir-Blodgett (LB) technique, and the cotransfer of the enzyme was confirmed with fluorescence spectroscopy. The catalytic activity of asparaginase in the LB films was studied with UV-vis spectroscopy, which showed that the presence of CNT in the enzyme-lipid LB film not only tuned the catalytic activity, but also helped conserve its enzyme activity after weeks, showing higher persisting values of activity. UV-vis spectroscopy also showed that the catalytic activity is dependent basically on the enzyme molecules present on the surface of the LB films since multilayer films did not provide a proportional increase of enzyme activity. These results are related to the synergism between the compounds on the active layer, leading to a molecular architecture that allowed the adequate molecular accommodation of the analyte with the catalytic sites of the enzyme, which also preserved the asparaginase activity. This work then demonstrates the feasibility of employing LB films composed of fatty acids, CNT, and enzymes as devices for biosensing applications.

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.

Langmuir–Blodgett films of perylene bisimide derivatives and fluorescent recognition of diamines

A fluorescent film was constructed with the well-known Langmuir–Blodgett technique, and it showed exceptional sensing performances for some diamine vapors.

Adsorption and enzyme activity of asparaginase at lipid Langmuir and Langmuir-Blodgett films

In this present work, the surface activity of the enzyme asparaginase was investigated at the air-water interface, presenting surface activity in high ionic strengths. Asparaginase was incorporated in Langmuir monolayers of the phospholipid dipalmitoylphosphatidylcholine (DPPC), forming a mixed film, which was characterized with surface pressure-area isotherms, surface potential-area isotherms, polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS), and Brewster angle microscopy (BAM). The adsorption of the enzyme at the air-water interface condensed the lipid monolayer and increased the film compressibility at high surface pressures. Amide bands in the PM-IRRAS spectra were identified, with the CN and CO dipole moments lying parallel to monolayer plane, revealing the structuring of the enzyme into α-helices and β-sheets. The floating monolayers were transferred to solid supports as Langmuir-Blodgett (LB) films and characterized with fluorescence spectroscopy and atomic force microscopy. Catalytic activities of the films were measured and compared to the homogenous medium. The enzyme accommodated in the LB films preserved more than 78% of the enzyme activity after 30days, in contrast for the homogeneous medium, which preserved less than 13%. The method presented in this work not only allows for an enhanced catalytic activity, but also can help explain why certain film architectures exhibit better performance.