Immobilization of alcohol dehydrogenase in phospholipid Langmuir-Blodgett films to detect ethanol

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.

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.

Conjugated polymers as Langmuir and Langmuir-Blodgett films: Challenges and applications in nanostructured devices

Initially developed for classic systems composed of fatty acids and phospholipids, the Langmuir and Langmuir-Blodgett (LB) techniques allow the fabrication of nanometer-scale devices at self-assembly interfaces with high control over the thickness and molecular architecture. Their application in the research and production of new plastic materials has grown considerably over the past few decades due to the efficiency of conjugated polymers (CPs) for the production of light-emitting diodes, flexible displays, solar cells, and other photoelectronic devices. The structuring of polymers at different interfaces is not trivial as this class of macromolecules can undergo through different processes of folding/unfolding, which hinders the formation of stable Langmuir monolayers and, consequently, the production of Langmuir-Blodgett films. With these ideas in mind, the present article aims to review a series of elements related to the formation of stable Langmuir and Langmuir-Blodgett films of CPs, especially those based on poly(phenylene vinylene)s, polyfluorenes, and polythiophenes. This review is divided into two parts where we first discuss the formation of neat CP films, and then the strategies for the formation of stable CP films based on the co-immobilization with fatty acids, other polymers, and enzymes as mixed films.

Physicochemical Characterization of Oleanolic Acid-Human Serum Albumin Complexes for Pharmaceutical and Biosensing Applications

Among numerous compounds found in marine organisms, triterpenes have attracted considerable research interest due to a beneficial impact on health including anti-inflammatory, antitumor, antiviral, and antioxidation effects. Specifically, new functionalities of oleanolic acid (OLA) have been revealed recently, indicating possible applications in nutrition and pharmaceuticals. However, this bioactive material has limited value due to low water solubility and stability. Therefore, oleanolic acid needs a carrier that protects it and enables controlled release in the human body. Innovative drug delivery systems provide a promising strategy for overcoming these problems. However, the development of those systems requires a comprehensive understanding of the physicochemical properties of triterpenes and their carriers as well as the interactions between them. Among numerous substances, human serum albumin (HSA) has been widely studied as a drug carrier. In addition, human serum albumin is the main blood plasma protein responsible for the transport of drugs and metabolites; therefore, the interactions between that protein and other substances are of physiological and pharmaceutical importance. Moreover, sensing the HSA level in blood plasma is an important challenge that requires binding studies on a molecular scale. The aim of this study was to investigate the properties of oleanolic acid in the presence of human serum albumin in terms of thermodynamics, morphology, and viscoelasticity at the air/water interface. Moreover, the wettability, surface free energy, and topography of the films after deposition on the solid substrate were determined. The results have been discussed in terms of providing physicochemical insight into the interfacial behavior of the OLA-HSA complex, which is crucial for pharmaceutical and bioanalytical applications.

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.

Temperature, pH, and Molecular Packing Effects on the Penetration of Oleic Acid Monolayer by α-Lactalbumin

Recently, we reported on the interfacial behavior of mixed oleic acid (OA)-α-lactalbumin monolayer and its relevance in the formation of tumoricidal HAMLET (human α-lactalbumin made lethal to tumor cells)-like complex. This complex is probably formed in the gastrointestinal tract, but it has not been proved so far. The molecular base and the underlying physicochemical forces leading to such complexation remain to be known as well. There are also several other issues related with the complex stoichiometry that need to be fully explained. This study provides insight into the mechanism of temperature, pH, and physical state of monolayer-dependent binding of OA by the milk protein- apo-α-lactalbumin. Using the Langmuir and Langmuir-Blodgett approaches, we investigated the interactions between the OA monolayer and the apo-bovine α-lactalbumin (BLA III) at different pH, temperatures, and molecular packing. We found that the most favorable conditions for the formation of mixed OA-BLA III film are relevant to the gastric environment. The stabilization of OA-BLA III at the interface is associated with the conformational changes of protein in the presence of fatty acids induced by low pH and high temperature in the expanded monolayer. Our approach helps to understand the molecular mechanism of HAMLET/bovine α-lactalbumin made lethal to tumor cells formation in vivo.

Novel Perfluorinated Triblock Amphiphilic Copolymers for Lipid-Shelled Microbubble Stabilization

Amphiphilic triblock (Atri) copolymers made of perfluorinated alkyl chain linked to hydrocarbon chain and methoxy-poly(ethylene glycol) of three different molecular weights were synthesized. In vitro evaluation demonstrated that these new compounds were noncytotoxic. Characterization and interaction of each triblock copolymer with a branched polyamine myristoyl lipid (2-{3[bis-(3-amino-propyl)-amino]-propylamino}- N-ditetradecyl carbamoyl methyl-acetamide, DMAPAP) were studied by the Langmuir film method and thermal analysis. The triblock copolymer/cationic lipids (1:10, w/w) were mixed with perfluorobutane gas to form microbubbles (MBs). The latter were characterized by optical microscopy to get the microbubble size and concentration by densimetry to determine the amount of encapsulated gas and by ultrasound to assess oscillation properties. Atri with the lowest and intermediate weights were shown to interact with the cationic lipid DMAPAP and stabilize the Langmuir film. In that case, monodisperse microbubbles ranging from 2.3 ± 0.1 to 2.8 ± 0.1 μm were obtained. The proportion of encapsulated gas within the MB shell increased up to 3 times after the incorporation of the copolymer with the lowest and intermediate weights. Moreover, the acoustic response of the microbubbles was maintained in the presence of the copolymers.

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.

Mesoporous carbon nitride based biosensor for highly sensitive and selective analysis of phenol and catechol in compost bioremediation

Herein, we reported here a promising biosensor by taking advantage of the unique ordered mesoporous carbon nitride material (MCN) to convert the recognition information into a detectable signal with enzyme firstly, which could realize the sensitive, especially, selective detection of catechol and phenol in compost bioremediation samples. The mechanism including the MCN based on electrochemical, biosensor assembly, enzyme immobilization, and enzyme kinetics (elucidating the lower detection limit, different linear range and sensitivity) was discussed in detail. Under optimal conditions, GCE/MCN/Tyr biosensor was evaluated by chronoamperometry measurements and the reduction current of phenol and catechol was proportional to their concentration in the range of 5.00 × 10(-8)-9.50 × 10(-6)M and 5.00 × 10(-8)-1.25 × 10(-5)M with a correlation coefficient of 0.9991 and 0.9881, respectively. The detection limits of catechol and phenol were 10.24 nM and 15.00 nM (S/N=3), respectively. Besides, the data obtained from interference experiments indicated that the biosensor had good specificity. All the results showed that this material is suitable for load enzyme and applied to the biosensor due to the proposed biosensor exhibited improved analytical performances in terms of the detection limit and specificity, provided a powerful tool for rapid, sensitive, especially, selective monitoring of catechol and phenol simultaneously. Moreover, the obtained results may open the way to other MCN-enzyme applications in the environmental field.

Serum albumin in 2D: a Langmuir monolayer approach

Understanding of protein interaction at the molecular level raises certain difficulties which is the reason a model membrane system such as the Langmuir monolayer technique was developed. Ubiquitous proteins such as serum albumin comprise 50% of human blood plasma protein content and are involved in many biological functions. The important nature of this class of protein demands that it be studied in detail while modifying the experimental conditions in two dimensions to observe it in all types of environments. While different from bulk colloidal solution work, the two dimensional approach allows for the observation of the interaction between molecules and subphase at the air-water interface. Compiled in this review are studies which highlight the characterization of this protein using various surroundings and also observing the types of interactions it would have when at the biomembrane interface. Free-energy changes between molecules, packing status of the bulk analyte at the interface as well as phase transitions as the monolayer forms a more organized or aggregated state are just some of the characteristics which are observed through the Langmuir technique. This unique methodology demonstrates the chemical behavior and physical behavior of this protein at the phase boundary throughout the compression of the monolayer.

Vibrational spectroscopy for probing molecular-level interactions in organic films mimicking biointerfaces

Investigation into nanostructured organic films has served many purposes, including the design of functionalized surfaces that may be applied in biomedical devices and tissue engineering and for studying physiological processes depending on the interaction with cell membranes. Of particular relevance are Langmuir monolayers, Langmuir-Blodgett (LB) and layer-by-layer (LbL) films used to simulate biological interfaces. In this review, we shall focus on the use of vibrational spectroscopy methods to probe molecular-level interactions at biomimetic interfaces, with special emphasis on three surface-specific techniques, namely sum frequency generation (SFG), polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) and surface-enhanced Raman scattering (SERS). The two types of systems selected for exemplifying the potential of the methods are the cell membrane models and the functionalized surfaces with biomolecules. Examples will be given on how SFG and PM-IRRAS can be combined to determine the effects from biomolecules on cell membrane models, which include determination of the orientation and preservation of secondary structure. Crucial information for the action of biomolecules on model membranes has also been obtained with PM-IRRAS, as is the case of chitosan removing proteins from the membrane. SERS will be shown as promising for enabling detection limits down to the single-molecule level. The strengths and limitations of these methods will also be discussed, in addition to the prospects for the near future.

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.

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.

Quantification of prothrombin in human plasma amplified by autocatalytic reaction

By site directed mutagenesis, we have produced recombinant mutants of human and mouse prethrombin-2 which are able to convert themselves autocatalytically into α-thrombin. We also have created a new method to amplify the signal of bioanalytical assays based on the autocatalytic activation of these mutated proenzymes. The activation of the mutants by active α-thrombin triggers an autocatalytic reaction which leads to more active thrombin resulting in the amplification of the readout signal. Addition of mutated mouse prethrombin-2 into the conventional assay for prothrombin level in human plasma, employing ecarin and the fluorogenic substrate, resulted in improvement of the detection limit by 2 orders of magnitude.

Recent advances in electronic tongues

This minireview describes the main developments of electronic tongues (e-tongues) and taste sensors in recent years, with a summary of the principles of detection and materials used in the sensing units. E-tongues are sensor arrays capable of distinguishing very similar liquids employing the concept of global selectivity, where the difference in the electrical response of different materials serves as a fingerprint for the analysed sample. They have been widely used for the analysis of wines, fruit juices, coffee, milk and beverages, in addition to the detection of trace amounts of impurities or pollutants in waters. Among the various principles of detection, electrochemical measurements and impedance spectroscopy are the most prominent. With regard to the materials for the sensing units, in most cases use is made of ultrathin films produced in a layer-by-layer fashion to yield higher sensitivity with the advantage of control of the film molecular architecture. The concept of e-tongues has been extended to biosensing by using sensing units capable of molecular recognition, as in films with immobilized antigens or enzymes with specific recognition for clinical diagnosis. Because the identification of samples is basically a classification task, there has been a trend to use artificial intelligence and information visualization methods to enhance the performance of e-tongues.

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

A major challenge for producing low cost biosensors based on nanostructured films with control of molecular architectures is to preserve the catalytic activity of the immobilized biomolecules. In this study, we show that catalase (HRP) keeps its activity if immobilized in Langmuir-Blodgett (LB) films of dipalmitoyl phosphatidylglycerol (DPPG). The incorporation of catalase into a DPPG monolayer at the air-water interface was demonstrated with surface pressure and surface potential isotherms, in addition to polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). According to the PM-IRRAS data, catalase was not denatured upon adsorption on a preformed DPPG monolayer and could be transferred onto a solid substrate. The catalytic activity of catalase in a mixed LB film with DPPG was ca. 13% higher than in solution. The control of molecular architecture and choice of a suitable phospholipid matrix allows catalase-containing LB films to be used in sensing hydrogen peroxide.

Langmuir-Blodgett films of pyridyldithio-modified multiwalled carbon nanotubes as a support to immobilize hydrogenase

Pyridylthio-modified multiwalled carbon nanotubes (pythio-MWNTs) have been prepared by a reaction of the oxidized MWNTs with S-(2-aminoethylthio)-2-thiopyridine hydrochloride. The obtained pythio-MWNTs nanocomposites formed stable floating monolayers at the air-water interface, which were transferred onto substrate surfaces by the Langmuir-Blodgett (LB) method. Compositions and morphologies of the LB films were characterized by absorption, Raman, X-ray photoelectron spectra as well as by scan electron microscopy and atomic force microscopy. These pythio-MWNTs LB films were then used as a support to immobilize hydrogenase (H(2)ase) to form bionanocomposite of pythio-MWNTs-H(2)ase. Cyclic voltammograms for indium tin oxide electrode covered with the pythio-MWNTs-H(2)ase films were investigated in both Ar and H(2) saturated 0.05 M KCl electrolyte solutions at pH from 4.0 to 9.0. A reversible redox couple of [4Fe-4S](2+/1+) clusters of H(2)ase was recorded when the pH value was 6.0 and 9.0, with reduction and oxidation potentials appearing at about -0.70 and -0.35 V vs Ag/AgCl, respectively. It was revealed that the H(2)ase was of high catalytic activity and strong stability in the LB films of pythio-MWNTs-H(2)ase. Hence, we suggested that the present bionanocomposites could be used as heterogeneous biocatalyst to catalyze reversible reaction between protons and H(2), resulting in potential applications in biohydrogen evolution and H(2) biofuel cells.