Enzyme activity of catalase immobilized in Langmuir-Blodgett films of phospholipids

Using Carbon Nanotubes to Improve Enzyme Activity and Electroactivity of Fatty Acid Langmuir-Blodgett Film-Incorporated Galactose Oxidase for Sensing and Energy Storage Applications

Incorporating enzymes into nanostructured supercapacitor devices represents a groundbreaking advancement in energy storage. Enzyme catalysis using nanomaterials enhances performance, efficiency, and stability by facilitating precise charge transfer, while the nanostructure provides a high surface area and improved conductivity. This synergy yields eco-friendly, high-performance energy storage solutions crucial for diverse applications, from portable electronics to renewable energy systems. In this study, we harnessed the versatility of Langmuir-Blodgett films to create meticulously organized thin films with specific enzyme properties, coupled with carbon nanotubes, to develop biosupercapacitors. Langmuir monolayers were constructed with stearic acid, carbon nanotubes, and galactose oxidase. Following comprehensive characterization using tensiometric, rheological, morphological, and spectroscopic techniques, the monolayers were transferred to solid supports, yielding Langmuir-Blodgett films. These films exhibited superior performance, with persisting enzyme activity. However, increasing film thickness did not enhance enzymatic activity values, indicating a surface-driven process. Subsequently, we explored the electrochemical properties of the films, revealing stability compatible with supercapacitor applications. The introduction of carbon nanotubes demonstrated a higher capacitance, indicating the potential viability of the films for energy storage applications.

Surface characterization and interfacial activity of chitinase chi18-5 against chitosan in langmuir monolayers

One of the challenges for producing active chitinase formulations relies on the gap between the laboratory tests and the biological scenarios where the enzyme will perform its function. In this work, we have employed different Langmuir monolayer arrays to evaluate the interfacial behavior of a recently purified recombinant chitinase, Chi18-5. We have demonstrated that two conformations exist for the chitinase at pH values close to its pI, showing very distinct structural properties at the air/aqueous interface. Enzyme activity was assessed by implementing different kinetic approaches and using a chitosan-1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) mixed film as organized substrate model membrane. Combining these strategies, we demonstrated that better catalytic efficiencies can be obtained for Chi18-5 at pH 5. Moreover, the chitinase activity at the air/aqueous interface can be tuned by introducing in situ pH modifications over the surrounding milieu. We also studied the changes in the topography at the mesoscale level using Brewster Angle Microscopy (BAM). We found that Chi18-5 segregated onto the chitosan domains of the membrane, showing differences in homogeneity depending on the pH imposed. Alternatively, pure Chi18-5 was tested for immobilization onto a hydrophilic activated solid support using the Langmuir-Blodgett technique. Atomic Force Microscopy (AFM) analyses showed successfully stabilization and preservation of molecular features attributed to the pH at which the enzyme deposition was performed.

Graphene Oxide-Cytochrome c Multilayered Structures for Biocatalytic Applications: Decrypting the Role of Surfactant in Langmuir-Schaefer Layer Deposition

Graphene, a two-dimensional single-layer carbon allotrope, has attracted tremendous scientific interest due to its outstanding physicochemical properties. Its monatomic thickness, high specific surface area, and chemical stability render it an ideal building block for the development of well-ordered layered nanostructures with tailored properties. Herein, biohybrid graphene-based layer-by-layer structures are prepared by means of conventional and surfactant-assisted Langmuir-Schaefer layer deposition techniques, whereby cytochrome c molecules are accommodated within ordered layers of graphene oxide. The biocatalytic activity of the as-developed nanobio-architectures toward the enzymatic oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt and decolorization of pinacyanol chloride is tested. The results show that the multilayer structures exhibit high biocatalytic activity and stability in the absence of surfactant molecules during the deposition of the monolayers.

Conjugated Polymers Blended with Lipids and Galactosidase as Langmuir-Blodgett Films To Control the Biosensing Properties of Nanostructured Surfaces

The structure of enzymes must be conserved when incorporated in nanoelectronic devices because their activity determines the function of the device as sensors. Among the systems that can retain their conformational structures, Langmuir-Blodgett (LB) films can be useful to exploit the construction of bioelectronic devices organized at the molecular level because biological and polymeric materials can be coupled as ultrathin films for biosensors and actuators. In this paper, we immobilized a β-galactosidase enzyme in the LB films of stearic acid and the conjugated polymer poly[(9,9-dioctylfluorene)- co-thiophene]. After the characterization of the floating films using tensiometry, vibrational spectroscopy, and Brewster angle microscopy, they were transferred to solid supports as LB films, and the catalytic activity of the enzyme could be preserved as analyzed using UV-vis spectroscopy. We noted that the presence of a supramolecular structure formed in the LB films not only conserved the enzyme activity but also exhibited regular and distinctive output signals in all molecular architectures employed in this work. These results are related to the synergism between the compounds on the active layer associated with a surface morphology that facilitated the analyte diffusion because of an adequate molecular accommodation of all components. This work then demonstrates the viability of employing LB films composed of lipids, enzymes, and synthetic polymers as devices for biosensing applications.

Unique supramolecular assembly through Langmuir - Blodgett (LB) technique

The Langmuir-Blodgett (LB) technique is a way of making supra-molecular assembly in ultrathin films with a controlled layered structure and crystal parameter, which have many envisioned technological applications for optical and molecular electronic devices as well as signal processing and transformation. Probably LB technique is the best method to manipulate materials at molecular level and provides a scope to realize the molecular electronics in reality. In this review article, we have discussed about the general introduction of LB technique and recent development on LB and related system including (i) LB methodology, (ii) characterizations of LB films, (iii) LB films and molecular electronics, (iv) historical review of LB films, (v) research and applications including fundamental research and application towards devices.

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.

Multisensor systems based on phthalocyanines for monitoring the quality of grapes

Arrays of phthalocyanine-based sensors with complementary activity have been used to develop voltammetric electronic tongues. Such systems have demonstrated to be useful in enology for the evaluation of quality of wines in different production stages, from grapes to bottles. In this paper, the state of the art of multisensor systems based on phthalocyanines dedicated to the analysis of musts (juices obtained from crushed grapes) is described. Such multisensor systems cover different types of sensors from simple Carbon Paste Electrodes, to sophiticated nanostructured sensors, including Langmuir–Blodgett or Layer by Layer thin films and biomimetic biosensors where phthalocyanines play a crucial role as electron mediator between enzymes and electrodes. In all cases, multisensor systems based on phthalocyanines have been able to discriminate musts prepared from different varieties of grapes. The performance of these systems can be improved by combining non-specific sensors with biosensors containing enzymes selective to phenols. In this case, excellent relationships have been found between the responses provided by the array and the content in phenols and acids provided by traditional chemical analysis.

Array of biosensors for discrimination of grapes according to grape variety, vintage and ripeness

A bioelectronic tongue based on nanostructured biosensors specific for the simultaneous detection of sugars and phenols has been developed. The array combined oxidases and dehydrogenases immobilized on a lipidic layer prepared using the Langmuir-Blodgett technique where Glucose oxidase, d-Fructose dehydrogenase, Tyrosinase or Laccase were imbibed. A phthalocyanine was co-immobilized in the sensing layer and used as electron mediator. The array thus formed has been used to analyze grapes and provides global information about the samples while providing specific information about their phenolic and their sugar content. Using Principal Component Analysis (PCA) the array of voltammetric biosensors has been successfully used to discriminate musts prepared from different varieties of grapes (Tempranillo, Garnacha, Cabernet-Sauvignon, Prieto Picudo and Mencía). Differences could be also detected between grapes of the same variety and cultivar harvested in two successive vintages (2012 and 2013). Moreover, the ripening of grapes could be monitored from veraison to maturity due to the changes in their phenolic and sugar content. Using Partial Least Squares (PLS-1) analysis, excellent correlations have been found between the responses provided by the array of biosensors and classical parameters directly related to phenols (total polyphenol index, TPI) and sugar concentration (degree Brix) measured by chemical methods with correlation coefficients close to 1 and errors close to 0. It is also worthy to notice the good correlations found with parameters associated with the pH and acidity that can be explained by taking into account the influence of the pH in the oxidation potentials of the phenols and in the enzymatic activity. This bioelectronic tongue can assess simultaneously the sugar and the phenolic content of grapes and could be used to monitor the maturity of the fruit and could be adapted easily to field analysis.

Improvement of electrocatalytic effect in voltammetric sensors based on phthalocyanines

Voltammetric sensors based on phthalocyanines have been used to detect a variety of compounds. In this paper, the state of the art of sensors prepared using classical techniques will be revised. Then, new strategies to improve the performance of the sensors will be described using as example sensors chemically modified with lutetium bisphthalocyanine (LuPc[Formula: see text] dedicated to the detection of phenols of interest in the food industry. Classical LuPc2 carbon paste electrodes can detect phenols such as catechol, caffeic acid or pyrogallol with limits of detection in the range of 10[Formula: see text]–10[Formula: see text] M. The performance can be improved by using nanostructured Langmuir–Blodgett (LB) or Layer by Layer (LbL) films. The enhanced surface to volume ratio produce an increase in the sensitivity of the sensors. Limits of detection of 10[Formula: see text]–10[Formula: see text] M are attained, which are one order of magnitude lower than those obtained using conventional carbon paste electrodes. Moreover, these techniques can be used to co-immobilize two electrocatalytic materials in the same device. The limits of detection obtained in LB sensors combining LuPc2/AuNPs or LuPc2/CNT are further improved. Finally, the LB technique has been used to prepare biosensors where a phenol oxydase (such as tyrosinase or lacasse) is immobilized in a biomimetic environment that preserves the enzymatic activity. Moreover, LuPc2 can be co-immobilized with the enzyme in a lipidic film formed by arachidic acid (AA). LuPc2 can act as an electron mediator facilitating the electron transfer. These biomimetic sensors formed by LuPc2/AA/enzyme show Limits of detection of 10[Formula: see text] M and an enhanced selectivity.

Nanomaterials for diagnosis: challenges and applications in smart devices based on molecular recognition

Clinical diagnosis has always been dependent on the efficient immobilization of biomolecules in solid matrices with preserved activity, but significant developments have taken place in recent years with the increasing control of molecular architecture in organized films. Of particular importance is the synergy achieved with distinct materials such as nanoparticles, antibodies, enzymes, and other nanostructures, forming structures organized on the nanoscale. In this review, emphasis will be placed on nanomaterials for biosensing based on molecular recognition, where the recognition element may be an enzyme, DNA, RNA, catalytic antibody, aptamer, and labeled biomolecule. All of these elements may be assembled in nanostructured films, whose layer-by-layer nature is essential for combining different properties in the same device. Sensing can be done with a number of optical, electrical, and electrochemical methods, which may also rely on nanostructures for enhanced performance, as is the case of reporting nanoparticles in bioelectronics devices. The successful design of such devices requires investigation of interface properties of functionalized surfaces, for which a variety of experimental and theoretical methods have been used. Because diagnosis involves the acquisition of large amounts of data, statistical and computational methods are now in widespread use, and one may envisage an integrated expert system where information from different sources may be mined to generate the diagnostics.

Cellulase and alcohol dehydrogenase immobilized in Langmuir and Langmuir-Blodgett films and their molecular-level effects upon contact with cellulose and ethanol

The key challenges for producing devices based on nanostructured films with control over the molecular architecture are to preserve the catalytic activity of the immobilized biomolecules and to provide a reliable method for determining the intermolecular interactions and the accommodation of molecules at very small scales. In this work, the enzymes cellulase and alcohol dehydrogenase (ADH) were coimmobilized with dipalmitoylphosphatidylcholine (DPPC) as Langmuir-Blodgett (LB) films, and their biological activities were assayed by accommodating the structure formed in contact with cellulose. For this purpose, the polysaccharide was dissolved in an ionic liquid, 1-buthyl-3-methylimidazolium chloride (BMImCl), and dropped on the top of the hybrid cellulase-ADH-DPPC LB film. The interactions between cellulose and ethanol, which are the catalytic substrates of the enzymes as well as important elements in the production of second-generation fuels, were then investigated using polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS). Investigation of the secondary structures of the enzymes was performed using PM-IRRAS, through which the presence of ethanol and cellulose was observed to highly affect the structures of ADH and cellulase, respectively. The detection of products formed from the catalyzed reactions as well as the changes of secondary structure of the enzymes immobilization could be carried out, which opens the possibility to produce a means for producing second-generation ethanol using nanoscale arrangements.

Adsorption and enzyme activity of sucrose phosphorylase on lipid Langmuir and Langmuir-Blodgett films

The production of bioelectronic devices, including biosensors, can be conducted using enzymes immobilized in ultrathin solid films, for which preserving the enzymatic catalytic activity is crucial for optimal performance. In this sense, nanostructured films that allow for control over molecular architectures are of interest. In this paper, we investigate the adsorption of sucrose phosphorylase onto Langmuir monolayers of the phospholipid dimyristoylphosphatidic acid, which caused the surface pressure isotherms to expand. With polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS), the amide bands from the enzyme could be identified, with the C-N and C=O dipole moments lying parallel to the air-water interface. Structuring of the enzyme into an α-helix was noted, and this structure was preserved when the mixed enzyme-phospholipid monolayer was transferred in the form of a Langmuir-Blodgett (LB) film. The latter was demonstrated with measurements of the catalytic activity of sucrose phosphorylase, which presented the highest enzyme activity for multilayer LB film. The approach presented in this study not only allows for optimized catalytic activity toward sucrose but also permits to explain why certain film architectures exhibit superior performance.

High enzymatic activity preservation with carbon nanotubes incorporated in urease-lipid hybrid Langmuir-Blodgett films

The search for optimized architectures, such as thin films, for the production of biosensors has been challenged in recent decades, and thus, the understanding of molecular interactions that occur at interfaces is essential to improve the construction of nanostructured devices. In this study, we investigated the possibility of using carbon nanotubes in hybrid Langmuir-Blodgett (LB) films of lipids and urease to improve the catalytic performance of the immobilized enzyme. The molecular interactions were first investigated at the air-water interface with the enzyme adsorbed from the aqueous subphase onto Langmuir monolayers of dimyristoylphosphatidic acid (DMPA). The transfer to solid supports as LB films and the subsequent incorporation of carbon nanotubes in the hybrid film permitted us to evaluate how these nanomaterials changed the physical properties of the ultrathin film. Colorimetric measurments indicated that the presence of nanotubes preserved and enhanced the enzyme activity of the film, even after 1 month. These results show that the use of such hybrid films is promising for the development of biosensors with an optimized performance.

Monolayer collapse regulating process of adsorption-desorption of palladium nanoparticles at fatty acid monolayers at the air-water interface

In this paper, we investigate the affinity of palladium nanoparticles, stabilized with glucose oxidase, for fatty acid monolayers at the air-water interface, exploiting the interaction between a planar system and spheroids coming from the aqueous subphase. A decrease of the monolayer collapse pressure in the second cycle of interface compression proved that the presence of the nanoparticles causes destabilization of the monolayer in a mechanism driven by the interpenetration of the enzyme into the bilayer/multilayer structure formed during collapse, which is not immediately reversible after monolayer expansion. Surface pressure and surface potential-area isotherms, as well as infrared spectroscopy [polarization modulation infrared reflection adsorption spectroscopy (PM-IRRAS)] and deposition onto solid plates as Langmuir-Blodgett (LB) films, were employed to construct a model in which the nanoparticle has a high affinity for the hydrophobic core of the structure formed after collapse, which provides a slow desorption rate from the interface after monolayer decompression. This may have important consequences on the interaction between the metallic particles and fatty acid monolayers, which implies the regulation of the multifunctional properties of the hybrid material.

Biocatalysts immobilized in ultrathin ordered films

The immobilization of enzymes and other proteins into ordered thin materials has attracted considerable attention over the past few years. This research has demonstrated that biomolecules immobilized in different [Langmuir-Blodgett (LB)/Langmuir-Schaefer (LS)] matrixes retain their functional characteristics to a large extent. These new materials are of interest for applications as biosensors and biocatalysts. We review the growing field of oxidases immobilized onto ordered Langmiur-Blodgett and Langmuir-Schaefer films. Strategies for the preparation of solid supports and the essential properties of the resulting materials with respect to the envisaged applications are presented. Basic effects of the nature of the adsorption and various aspects of the application of these materials as biosensors, biocatalysts are discussed. Outlook of potential applications and further challenges are also provided.