1. Conjugated polymers blended with lipids and galactosidase as Langmuir-Blodgett films to control the biosensing properties of nanostructured surfaces
Author: Felipe Tejada Araujo, Laura Oliveira Péres, and Luciano Caseli
Abstract: The structure of enzymes must be conserved when incorporated in nano-electronic devices since their activity determines the device’s function as sensors. Among the systems able to keep their conformational structures, Langmuir-Blodgett (LB) films can be useful to exploit the construction of bioelectronics devices organized at the molecular level since biological and polymeric materials can be coupled as ultrathin films for biosensors and actuators. In this paper, we immobilized a beta-galactosidase enzyme in 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 supramolecular structure formed in the LB film 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 to a surface morphology that facilitated the analyte diffusion due to 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.
2. Interaction of Trastuzumab with biomembrane models at air-water interfaces mimicking cancer cell surfaces
Authors: Andrei Sakai, Ana Paulade Sousa Mesquista, Erica Valadaresde Castro Levatti, Anita Hilda Straus, Helena B.Nader, Carla Cristina Lopes and Luciano Caseli
Journal: Biochimica et Biophysica Acta (BBA) – Biomembranes
Abstract: Trastuzumab (Tmab) is a monoclonal antibody administered as targeted therapy for HER2-positive breast cancer whose molecular interactions at the HER2 receptor microenvironment are not completely clarified yet. This paper describes the influence of Tmab in the molecular organization of films of biological-relevant molecules at the air water interface. For that, we spread components of tumorigenic and non-tumorigenic cells directly on the air-water interface. The physicochemical properties of the films were investigated with surface pressure-area isotherms and Brewster angle microscopy, and distinction between the cellular lines with higher or lower amount of HER2 could be detected based on the physicochemical properties of the interfacial films. The systems organized at the air-water interface were transferred to solid supports as Langmuir-Blodgett films and the nano-scale morphology investigated with atomic force microscopy. The overall results related to Tmab interacting with the films lead to the conclusion that Tmab tends to condense rich-HER2 films, causing irregular dimerization of the receptor protein, changing the membrane topography of the films, with formation of phases with different levels of reflectivity and aggregation morphology, and finally revealing that the interaction of the antibody with proteo-lipidic biointerfaces is modulated by the film composition. We believe that novel perspectives concerning the molecular interactions in the plasma membrane microenvironment through Langmuir monolayers can be obtained from this work in order to enhance the Tmab-based cancer therapy.
3. Strong polarity asymmetry and abnormal mechanical electroresistance effect in organic monolayer tunnel junction
Authors: Gelei Jiang, Yun Chen, Ye Ji, Weijin Chen, Xiaoyue Zhang and Yue Zheng
Journal: ACS Applied Electronic Materials
Abstract: The performance of organic polar tunnel junctions under external electrical/mechanical stimuli is crucial for their great promising in developing flexible and high-performance sensor and memristive devices. Here, we prepared a single P(VDF-TrFE) monolayer on an Au(111) atomic-level surface by using a Langmuir-Blodgett (LB) technique. The polarity stability and electronic transport behavior of the monolayer was investigated via piezoresponse force microscopy (PFM) and conductive atomic force microscopy (c-AFM) measurements. We observed a strong polarity asymmetry in the P(VDF-TrFE) monolayer tunnel junction. Electrical bias as well as mechanical force exerted by the tip both can switch the monolayer from metastable state (“H-Au” state, down polarity) to the stable (“F-Au” state, up polarity). Moreover, the conductance of the monolayer tunnel junction can be controlled not only by the electrical bias, but also by the tip force. Interestingly, a decrease of conductance from ON state to OFF state is caused by the tip force, which is against our common sense that the larger the tip force the larger tunnel conductance. This abnormal mechanical electroresistance effect is attributed to the strong asymmetric interfacial barriers.
4. Facile Preparation of Self-Assembled Layered Double Hydroxide-Based Composite Dye Films as New Chemical Gas Sensors
Authors: Ying He, Ran Wang, Tifeng Jiao, Xiaoya Yan, Mingli Wang, Lexin Zhang, Zhenhua Bai, Qian Zhang and Qiuming Peng
Journal: ACS Sustainable Chemistry & Engineering
Abstract: The useful functionalization and self-assembly of two-dimensional layered materials like hydrotalcite (LDH) are critical for the wide application of nanomaterials. In this work, some self-assembled Langmuir films of ion-exchanged LDH and dyes with different molecular structures were prepared by the Langmuir–Blodgett (LB) technique. The aggregation states of used dye molecules on the surface of the obtained membrane and the structures/properties of the membrane were studied. The hydroxyethyl sulfonate-inserted LDH (LDH-Ise) nanosheets were able to induce the dye formation of highly ordered H- and/or J-aggregate structures. Surface-enhanced Raman scattering (SERS) spectroscopy results demonstrated the uniformity and repeatability of the film. Interestingly, the good acid–base gas response characteristics of present LDH-Ise/dye LB films were investigated by UV-Vis and FT-IR. Present research works provide new clues for the development of gas sensors and chemical switches as well as the preparation of effective functional self-assembled films.
5. Influence of levofloxacin and clarithromycin on the structure of DPPC monolayers
Authors: Stephanie Ortiz-Collazos, Paulo H.S.Picciani, Osvaldo N.Oliveira Jr, Andre S.Pimentel and Karen J.Edler
Journal: Biochimica et Biophysica Acta (BBA) – Biomembranes
Abstract: Research on lipid/drug interactions at the nanoscale underpins the emergence of synergistic mechanisms for topical drug administration. The structural understanding of bio-mimetic systems employing 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) as a lung surfactant model mixed with antibiotics, as well as their biophysical properties, is of critical importance to modulate the effectiveness of therapeutic agents released directly to the airways. In this paper, we investigate the structural details of the interaction between Levofloxacin, ‘a respiratory quinolone’, and the macrolide Clarithromycin, with DPPC monolayers at the air-water interface, using a combination of Brewster angle microscopy, polarization modulation-infrared reflection-adsorption spectroscopy (PM-IRRAS), surface pressure isotherms and neutron reflectometry (NR) to describe the structural details of this interaction. The results allowed association of changes in the π-A isotherm profile with changes in the molecular organization and the co-localization of the antibiotics within the lipid monolayer by NR measurements. Overall, both antibiotics are able to increase the thickness of the acyl tails in DPPC monolayers with a corresponding reduction in tail tilt as well as to interact with the phospholipid headgroups as shown by PM-IRRAS experiments. The effects on the DPPC monolayers are correlated with the physical-chemical properties of each antibiotic and dependent on its concentration.
6. Enhancing Supramolecular Stability of Monolayers by Combining Dipolar with Amphiphilic Motifs: Case of Amphiphilic Push-Pull-Thiazole
Authors: Maximilian L Hupfer, Martin Kaufmann, Sylvio May, Julia Preiß, Dieter Weiss, Benjamin Dietzek, Rainer Beckert and Martin Presselt
Journal: Physical Chemistry Chemical Physics
Abstract: Equipping a thiazole dye with push and pull moieties adds dipolar intermolecular interactions and two hydrophilic anchors to a centrally anchored π-stacking and otherwise mono-amphiphilic dye. We show that, despite the resulting irregular shape of the tripodal amphiphile, the enhanced intermolecular interactions and amphiphilicity yields smooth and stable thin films. Further, we present a first approach for deriving supramolecular binding energies from Langmuir-Blodgett hysteresis data.
7. Cellulose Nanofiber Nanosheet Multilayers by the Langmuir–Blodgett Technique
Authors: M. Mahbubul Bashar, Hiroaki Ohara, Huie Zhu, Shunsuke Yamamoto, Jun Matsui, Tokuji Miyashita and Masaya Mitsuishi
Abstract: We describe a systematic approach for producing cellulose nanofiber (CNF) nanosheets using the Langmuir–Blodgett (LB) technique. The CNFs were obtained from sulfuric acid hydrolysis of commercially available microfibrillated cellulose. Needle-like CNFs, negatively charged by grafted sulfate groups, were maintained at the air–water interface, assisted by amphiphilic polymer, poly(N-dodecyl acrylamide) (pDDA). The CNFs produced a stable monolayer. The surface pressure increased steadily with a high collapse pressure of 50 mN m–1 when spread with formic acid and pDDA. The composite monolayers were transferred onto solid substrates as Y-type LB films using a vertical dipping method. Upstroke and downstroke transfer ratios of the films were, respectively, unity and 0.88, indicating that full coverage was achieved by the monolayer even for more than 200 layers. Results obtained using atomic force microscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy showed that CNF nanosheets possess well-defined layer structures with average monolayer thickness of 5.3 nm. The relative amount of CNFs in the nanosheets was calculated as 62.6 wt % using the quartz crystal microbalance technique. The as-prepared nanosheets are optically transparent to visible light and have high hydrophobicity. In fact, the nanosheet transparency was higher than 88% at 600 nm wavelength for 24 layers. A miniscule amount of pDDA enables demonstration of free-standing CNF nanosheets with 1 cm width and 45.6 nm thickness (23 layers).
8. In situ electrochemical and PM-IRRAS Studies of colicin E1 ion channels in the floating bilayer lipid membrane
Authors: Zhang Fei, Derek Ho, Allan Rod Merrill and Jacek Lipkowski
Abstract: Colicin E1 is a channel-forming bacteriocin produced by certain E. coli cells in an effort to reduce competition from other bacterial strains. The colicin E1 channel domain was incorporated into a 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) floating bilayer situated on a 1-thio--D-glucose modified gold (111) surface. The electrochemical properties of the colicin E1 channel in the floating bilayer were measured by electrochemical impedance spectroscopy (EIS); the configuration and orientation of colicin E1 in the bilayer were determined by polarization-modulation-infrared-reflection absorption spectroscopy (PM-IRRAS). The EIS and IR results indicate that colicin E1 adopts a closed channel state at the positive transmembrane potential, leading to high membrane resistance and a large tilt angle of -helices. When the transmembrane potential becomes negative, colicin E1 begins to insert into the lipid bilayer, corresponding to low membrane resistance and a low tilt angle of -helices. The insertion of colicin E1 into the lipid bilayer is driven by the negative transmembrane potential, and the ion channel open and closed states are potential reversible. The data in this report provide new insights into the voltage-gated mechanism of colicin E1 ion channels in phospholipid bilayers and illustrate that the floating bilayer lipid membrane at the metal electrode surface is a robust platform to study membrane-active proteins and peptides in a quasi-natural environment.
9. Preparation of Wrinkled Nanoribbons Consisting of Langmuir-Blodgett Films
Authors: Watanabe, Masashi
Journal: Journal of Nanoscience and Nanotechnology
Abstract: Langmuir-Blodgett films are normally deposited on hard substrates, such as mica plates. In this study, soft substrates consisting of a poly(dimethylsiloxane) elastomer were used for film deposition. A docosanoic acid monolayer was transferred onto the substrate by moving it in an upward direction while immersed in a subphase CoCl2 solution. Interestingly, the obtained deposited layer showed a ribbon-like morphology that oriented itself parallel to the water surface. Subsequently, by shrinking the substrate, wrinkled ribbons were obtained. This novel wrinkling method is unique to soft substrates because hard substrates cannot be shrunk. Such a wrinkling method can be useful to control the morphology of the LB films, and thus improve its properties as functional materials.
10. Sample Preparation for Transmission Electron Microscopy
Authors: Parastou Tizro, Cecilia Choi and Negar Khanlou
Abstract: Transmission electron microscopy (TEM) is an ideal device to study the internal structure of cells and different types of biological materials, but adverse conditions inside electron microscopes such as damage induced by electron bombardment and vacuum evaporation of structural water necessitates complex preparation methods to survive this environment. In order to introduce the sample into the evacuated microscope column, it should be stabilized and altered to small enough (about 3 mm in diameter) and thin enough parts to permit the transmission of electrons. Depending on applications different thicknesses are required; for example, in biological research studies usually 300–500 nm thickness is indicated. To stabilize the specimen and preserve the sample structures, different preparation methods are used involving different steps based on the type of study and the specimen, although the ultimate goal of all these preparation technics is to maintain the native structure of the sample. In this chapter, we try to explain the series of steps that involve in preparation. Virtually every step can affect the quality of sample, and therefore it is important to execute each step in detail.
11. Surface interactions determined by stereostructure on the example of 7-hydroxycholesterol epimers – The Langmuir monolayer study
Authors: Anna Chachaj-Brekiesz, Anita Wnętrzak, Ewelina Lipiec and Patrycja Dynarowicz-Latka
Journal: Biochimica et Biophysica Acta (BBA) – Biomembranes
Abstract: Stereoselective interactions are pivotal for molecular recognition between biomolecules and lipid surfaces. The aim of this study was to determine factors differencing molecular interactions between 7-hydroxycholesterol epimers (oxysterols, which excessively appear in pathological processes in human body) and natural membrane phospholipids. Two-component systems of different mutual proportions of 7-hydroxycholesterol (7α-hydroxycholesterol or 7-β-hydroxycholesterol, in short 7α-OH or 7β-OH) and membrane lipids (POPC, DPPC, DPPE, DPPS, SM) were systematically analyzed in artificial membranes modeled as Langmuir monolayers. Classical surface pressure measurements were complemented with direct visualization of films texture both in situ (with Brewster angle microscopy, BAM) and after their transfer onto solid supports (with Atomic Force Microscopy, AFM). Our results clearly show striking differences in surface properties of the studied binary mixtures, emphasizing distinct effects of both 7-hydroxycholesterol epimers on the organization of lipid layers. Systematic study allowed to conclude that the structure of polar head group and interfacial region of the molecule play important role in oxysterol-phospholipid interactions, while the hydrophobic region is significantly less important in this respect.