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

Studies on the Surface Adsorption of Binary Molten Salts

The surface adsorption of eight binary molten salts, AgNO3-M1NO3(M1 = Li, Na, K, Rb), NaNO3-M2NO3 (M2 = K, Rb), Ca(NO3)2-CsNO3, and Cd(NO3)2-NaNO3, has been investigated. It is found that the surface tension and temperature of molten salts at constant pressure and mole fraction satisfy the same equation as that for pure liquid compounds reported in our previous works. The heats of phase transition from the bulk to the surface phase for eight molten salts are determined. The heats per unit area are all at the order of -10-2 J/m2. The phase transition is exothermic because the entropy in the surface phase is smaller than the entropy in the bulk phase. The ratio of the solute surface concentration to the solute bulk concentration is approximated as the first-order polynomials of the solute bulk concentration. Then, curves of the surface tension vs the solute bulk concentration are well fitted. The ratio (ΔcBs/ΔcBα) is used to interpret the changing trend of the surface tension with bulk concentrations of solute. It is also found that the surface tension of molten salts decreases linearly with the solute surface concentration.

On the Preparation of Thin Films of Stearyl Methacrylate Directly Photo-polymerized at the Air-Water Interface

Characterization of bidimensional polymeric films at the air-water interface in the Langmuir trough, despite being a recurrent topic, usually refers to films of already formed polymeric materials, with very scarce reports on direct polymerization at the air-water interface. In the present work, we studied the photo-polymerization of stearyl methacrylate directly at the air-water interface under a nitrogen atmosphere, with the radical initiator solubilized in the aqueous phase. Two-dimensional (2D) polymerization was monitored by measuring the pressure-area isotherm at different irradiation times. The polymerization leads to a film with an isotherm different from that observed for the monomer, where the surface pressure is directly related to the irradiation time. The shape of this isotherm confirms the presence of a compressed liquid phase, where a higher order can be attained as a consequence of stronger packing forces involving polymer chains. The presence of inter-chain interactions allows rearrangements on the surface of the subphase, and even before the collapse a dense 2D ordering (with a solid phase-like behavior) can be observed. We present a new one-step, solvent-free procedure to obtain a photo-polymeric film directly at the air-water interface, which can be transferred to a solid surface by the Langmuir-Blodgett method, allowing film preparation of controlled thickness. Films were characterized by measuring properties such as thickness, roughness, and hydrophobicity and comparing them with films obtained from a conventional polymer. We report the differences between the interfacial behavior of amphiphilic molecules and nanomaterials such as films obtained by photo-polymerization, PSMA, directly on the air-water interface.

Glycopolymer-Based Materials: Synthesis, Properties, and Biosensing Applications

Glycopolymer materials have emerged as a significant biopolymer class that has piqued the scientific community's attention due to their potential applications. Recently, they have been found to be a unique synthetic biomaterial; glycopolymer materials have also been used for various applications, including direct therapeutic methods, medical adhesives, drug/gene delivery systems, and biosensor applications. Therefore, for the next stage of biomaterial research, it is essential to understand current breakthroughs in glycopolymer-based materials research. This review discusses the most widely utilized synthetic methodologies for glycopolymer-based materials, their properties based on structure–function interactions, and the significance of these materials in biosensing applications, among other topics. When creating glycopolymer materials, contemporary polymerization methods allow precise control over molecular weight, molecular weight distribution, chemical activity, and polymer architecture. This review concludes with a discussion of the challenges and complexities of glycopolymer-based biosensors, in addition to their potential applications in the future.

Unraveling interfacial properties of organic-coated marine aerosol with lipase incorporation

Marine aerosols are believed to have an organic surface coating on which fatty acids act as an important component due to their high surface activity. In addition, various kinds of enzyme species are abundantly found in seawater, some of which have been identified to exist in marine aerosols. Herein, from the perspective of marine aerosol interface simulation, we investigate the effect of Burkholderia cepacia lipase on the surface properties of stearic acid (SA) monolayer at the air-water interface by using surface-sensitive techniques of Langmuir trough and Infrared reflection-absorption spectroscopy (IRRAS). Our findings indicate that the stearic acid film undergoes a significant expansion, especially when the lipase concentration is 500 nM, because of the incorporation of lipase as observed from the surface pressure-area (π-A) isotherms. IRRAS spectra also show reduced intensities and ordering in the methylene stretching vibration region of stearic acid as a result of low surface density and disordered packing as the enzyme concentration increases. In particular, when the concentration of lipase is 500 nM, the lowest I_as/I_s values are shown on both pure water subphase and artificial seawater subphase, indicating more gauche conformations for SA. Furthermore, SA films with lipase incorporation were also studied at three different pH of subphase environment, considering the decrease of pH caused by the reaction with acidic gases during the aerosol aging process. The results reflect a more pronounced expansion of SA monolayer in acidic environment at pH 2.5, suggesting that hydrophobic interaction plays an important role in the disorder of the SA monolayer. In view of the coexistence of fatty acids and enzymes in the marine environment, this study provides a further understanding of the surface organization and behavior of organic-coated marine aerosols and deepen the knowledge of lipid-enzyme interfacial interactions occurring in the atmosphere.

Cationic Polythiophene-based Colorimetric Assay for Probing the Activity of Protein Kinase A

In this work, a novel colorimetric assay based on polythiophene derivative (PMNT) was designed for the detection of protein kinase A (PKA). PKA can catalyze the phosphorylation of peptide, leading to the conformation change of PMNT from random-coil to planar, with the disappearance of absorption peaks above 500 nm and a color change from pink to yellow. The fabricated assay exhibits a wide linear range of 0.05 - 20 U/mL with a detection limit of 0.02 U/mL for PKA activity detection. The proposed protocol has promising prospects for use in clinical diagnosis related to PKA activity.

Surface Chemistry Studies on the Formation of Mixed Stearic Acid/Phenylalanine Dehydrogenase Langmuir and Langmuir-Blodgett Films

This work investigates the physicochemical properties of mixed stearic acid (HSt)/phenylalanine dehydrogenase enzyme (PheDH) Langmuir films and their immobilization onto solid supports as Langmuir-Blodgett (LB) films. PheDH from the aqueous subphase enters the surfactant matrix up to an exclusion surface pressure of 25.3 mN/m, leading to the formation of stable and highly condensed mixed Langmuir monolayers. Hydrophobic interactions between the enzyme and HSt nonpolar groups tuned the secondary structure of PheDH, evidenced by the presence of β-sheet structures as demonstrated by infrared and circular dichroism spectra. The floating monolayers were successfully transferred to solid quartz supports, yielding Y-type LB films, and then characterized employing fluorescence, circular dichroism, and microscopic techniques, which indicated that PheDH was co-immobilized with HSt proportionally to the number of transferred layers. The enzyme fluidized the HSt monolayers, reducing their maximum dipoles when condensed to their maximum, and disorganized the alkyl chains of the fatty acid, as detected with infrared spectroscopy. The stability of the mixed floating monolayers enabled their transfer to solid supports as LB films, which is important for producing optical and electrochemical sensors for phenylalanine whose molecular architecture can be controlled with precision.

Interfacial behavior of Lactate Oxidase at Air-Subphase interface

This article investigates the main aspects of the surface chemistry properties of the lactate oxidase (LacOx) enzyme monolayer at the air-subphase interface. Surface chemistry study determined the important properties like the surface packing and stability of the formed layer, whereas the spectroscopic experiments provided information regarding its secondary structure conformation of the enzyme. We have demonstrated that the LacOx in the monolayer form remained active for extended time period. In accordance to the data obtained from the isotherm it was also found that LacOx forms a stable monolayer that does not aggregate at the air-subphase interface. The stability of the monolayer at the air-subphase interface was studied by using compression-decompression cycles which revealed the stability with no significant evidence of aggregates or irreversible domains. This was further confirmed by UV-vis absorption and fluorescence measurements. Spectra from circular dichroism (CD) showed that the LB film retains the characteristic of an α-helix conformation.

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.

Evaluation of the effects in cellular membrane models of antitrypanosomal poly-thymolformaldehyde (PTF) using Langmuir monolayers

The polymerization of bioactive compounds may be interesting because the supramolecular structures formed can boost biological action on microorganism membranes. In the present work, poly-thymolformaldehyde (PTF) activity, prepared by condensation of thymol and formaldehyde, was evaluated against trypomastigote forms of Trypanosoma cruzi and related with the physicochemical changes provided by the incorporation of the compound in protozoan cell membrane models. PTF exhibited an EC₅₀ value of 23.4 μg/mL and no toxicity against mammalian cells (CC₅₀ > 200 μg/mL). To understand the molecular action of PTF as an antiprotozoal candidate, this compound was incorporated in Langmuir monolayers of dipalmitoylphosphatidylglycerol (DPPG) as a model for parasite cell membranes. PTF shifted DPPG surface pressure-area isotherms to higher areas, indicating its incorporation in the lipid films. Additionally, it changed the thermodynamic, compressional, structural, and morphological properties of the floating monolayers, decreasing the collapse pressure, reducing the surface elasticity, and segregating molecules at the interface, forming domains with different reflectivities. Infrared spectroscopy showed that the lipid films with PTF presented an increased rate of gauche/all-trans conformers for the methylene groups from the acyl chains, indicating molecular disorder. Therefore, these results show that PTF alters the physicochemical properties of DPPG monolayers as a model for protozoa cell membranes, which can enhance the comprehension of the parasitic action of PTF against T. cruzi.

Studies of Langmuir and Langmuir-Schaefer Films of Poly(3-Hexylthiophene) and Poly(Vinylidene Fluoride)

The synergistic use of blends of regioregular poly(3-hexylthiophene) (P3HT) and poly(vinylidene fluoride) (PVDF) or poly((vinylidene fluoride)-block-(methyl methacrylate)) (PVDF-PMMA) to form Langmuir and Langmuir-Schaefer (LS) films is reported. P3HT has wide applications in sensor devices because of its properties such as conductivity, luminescence, and chromism; however, the stiffness of the films and the difficulty in organizing the molecules may pose a problem in these applications. In this context, polymers based on PVDF can be used in the formation of thin P3HT films and present an alternative to improve the organization of P3HT molecules. In addition, PVDF acts as a plasticizer, making the film less rigid. The films were obtained from the blends of P3HT/PVDF and P3HT/PVDF-PMMA in a solution containing chloroform and DMAc (N,N-dimethylacetamide). Surface pressure isotherms, in situ ultraviolet-visible (UV-vis) spectroscopy, polarization-modulation infrared reflection-absorption spectroscopy, and Brewster angle microscopy techniques were used to analyze Langmuir films. The surface morphology of LS films was characterized by atomic force microscopy and UV-vis spectroscopy, and their degradation was analyzed by UV-vis spectroscopy after exposure to natural light under atmospheric conditions. The Langmuir films containing PVDF indicate a direct formation of the ferroelectric β phase, with dipoles parallel to the water surface. The Langmuir films formed by P3HT presented dipoles of side chains parallel and aromatic groups perpendicular to the water surface. P3HT and PVDF or PVDF-PMMA films show high molecular organization compared with pure P3HT films. The results suggest that these films could be used to improve the properties of P3HT in several device applications, such as in optical and electrical sensors.

Molecular Information on the Potential of Europium Complexes for Local Recognition of a Nucleoside-Based Drug by Using Nanostructured Interfaces Assembled as Langmuir-Blodgett Films

The production of nanostructured materials for biological and medical applications may be applied toward the conjugation of adequate substances to boost the stimulus response of sensors and diagnostic probes. In this sense, Langmuir-Blodgett films constituted of bioinspired and biomimetic materials have attracted attention because of the ease of manipulation of the molecular architecture. In this paper, we employed a nucleoside-based drug, which was linked with a sterol hydrophobic moiety (3',4'-acetonide-uridine-succinate-cholesterol conjugate) to provide it an amphiphilic character. The drug was spread on the air-water interface, alone or mixed with stearic acid, forming Langmuir monolayers, and the complex Eu(tta)₃(H₂O)₂ was incorporated in the drug-containing monolayer. Interactions at the air-water interface between stearic acid, the drug, and the europium complex were then investigated with tensiometry, surface potential, infrared spectroscopy, and Brewster angle microscopy. The Langmuir films were transferred to solid supports as Langmuir-Blodgett films, which presented luminescent properties that could be tuned according to the molecular architecture. We believe that these results can serve as a novel approach to characterize and assemble materials organized in the molecular scale for medical applications.

Self-Assembled Polymeric Membranes and Nanoassemblies on Surfaces: Preparation, Characterization, and Current Applications

Biomembranes play a crucial role in a multitude of biological processes, where high selectivity and efficiency are key points in the reaction course. The outstanding performance of biological membranes is based on the coupling between the membrane and biomolecules, such as membrane proteins. Polymer-based membranes and assemblies represent a great alternative to lipid ones, as their presence not only dramatically increases the mechanical stability of such systems, but also opens the scope to a broad range of chemical functionalities, which can be fine-tuned to selectively combine with a specific biomolecule. Tethering the membranes or nanoassemblies on a solid support opens the way to a class of functional surfaces finding application as sensors, biocomputing systems, molecular recognition, and filtration membranes. Herein, the design, physical assembly, and biomolecule attachment/insertion on/within solid-supported polymeric membranes and nanoassemblies are presented in detail with relevant examples. Furthermore, the models and applications for these materials are highlighted with the recent advances in each field.