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.

Algal polysaccharides as matrices for the immobilization of urease in lipid ultrathin films studied with tensiometry and vibrational spectroscopy: Physical-chemical properties and implications in the enzyme activity.

Currently, many biological substances extracted from algae have received special attention because of their intrinsic characteristics, which can be applied to different areas of biotechnology. Therefore, in the current study, exopolysaccharides (EPS) from the microalgae Cryptomonas tetrapirenoidosa were employed as an aqueous subphase of a monolayer formed by the lipid dioctadecyldimethylammonium bromide (DODAB). The primary objective of this approach was to evaluate whether EPS could serve as a matrix for the immobilization of the enzyme urease to produce biosensors for urea. After DODAB was spread on the EPS solutions, urease was injected into the aqueous subphase, and the surface was submitted to compression using lateral barriers. The monolayers were subsequently characterized by surface pressure-area isotherms and polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS). The results indicated that EPS enhanced the adsorption of the enzyme on the lipid monolayer. The mixed films were later transferred to solid supports using the Langmuir-Blodgett (LB) technique and were characterized by transfer ratio, PM-IRRAS, quartz crystal microbalance, and atomic force microscopy. The immobilization of the enzyme on solid supports was fundamental for providing an ideal geometrical accommodation of urease because the interaction of EPS with urease in solution causes a decrease of the relative activity of urease. Therefore, these LB films are promising for the fabrication of future urea biosensors, the architecture of which can be manipulated and enhanced at the molecular level.