Bilayer Formation Research Articles

Stimulations inducing tethered lipid bilayer formation on protein‐modified substrate

AbstractSupported lipid bilayer (SLB) is one artificial biomembrane system used to study transportation reactions through biomembranes using solid devices and surface scientific methods. A key step in the SLB formation is the transformation of spherical lipid vesicles to a planar membrane. We investigated stimulation methods for adsorbed lipid vesicles on a streptavidin‐modified SiO2/Si substrate to induce tethered‐type SLB. We describe the effects of osmotic stress, Ca2+ addition, and a freeze–thaw cycle on the adsorbed vesicles, and on the condition of t‐SLB.

Structural, electronic and optical properties of CdO monolayer and bilayers: Stacking effect investigations

Abstract It is well known that the optoelectronic properties of two-dimensional (2D) materials may vary considerably by changing the layers number as well as the stacking order. In this work, the structural, electronic and optical properties of Cadmium oxide (CdO) monolayer and bilayers with different stacking orders are explored using first principles calculations. Simulations assert that the CdO single layer is a direct gap semiconductor with energy gap of 0.811 (1.883) eV as predicted by PBE(HSE06) functional. The bilayer formation leads to the considerable reduction of this parameter, however the direct nature is retained. Results show that the bilayers band gap depends strongly on the stacking order. The charge density maps are indicative of either chemical or physical interlayers interaction of the CdO bilayers. Our optical properties calculations show that the bilayers are more sensitive to the incident light than the monolayer, where the in-plane polarized light can excite more effectively the electronic transitions from the valence band to the conduction band. Additionally, the prospective optoelectronic applicability of the CdO 2D materials studied here is also demonstrated through the capability of absorbing a wide range of electromagnetic radiation with large absorption coefficient. Results reported here are useful covering the lack of knowledge on the optoelectronic properties of the CdO nanomaterials, and may be good guidance for the design of practical applications.

Asymmetry and Rippling in Mixed Surfactant Bilayers from All-Atom and Coarse-Grained Simulations: Interdigitation and Per Chain Entropy

Understanding lateral organizations of self-assembled bilayers is crucial to gain a control on functionally relevant topologies. We study self-assembled bilayers composed of a surfactant, behenyl trimethyl ammonium chloride (BTMAC), a cosurfactant, stearyl alcohol (SA), at a ratio of 2:1 in the presence of water at 283 K employing subsequent all-atom (AA) and coarse-grained (CG) molecular dynamics simulations. Differences in initial configurations lead to the formation of bilayers at ripple or square phases or interdigitated gel phases of varying trans-leaflet asymmetry. The AA ripple and gel phases are reproduced well at the CG level using bonded potentials from Boltzmann inversion of AA canonical sampling and nonbonded potentials from MARTINI. Inhomogeneous populations of disordered chains with higher per chain configurational entropy and tilt result in rippling stabilized by periodic hydrophobic energy barrier and strong interdigitation. Order parameters of the asymmetric bilayers are sufficiently coupled to the per chain entropies at both levels of resolutions to serve as a reflector of the per chain configurational entropy inaccessible by experiments. Thus, trans-bilayer asymmetry may be a controlling parameter to induce rippling in a bilayer of industrial importance. This work will be useful for future investigation on domain-associated transport and signaling in biomembranes at a low temperature.

Experimental and theoretical study of deactivated HDT catalysts by Si species deposited on their surfaces: Models proposition, structural and thermodynamic analysis

It is known that silicon species originate from the thermal degradation of the polydimethylsiloxane, adsorb on the catalysts surface used for hydrotreatment in the oil refining industry. This severely affects the performance of these catalysts and considerably reduce their lifetime. Combining 29Si and 13C CP/MAS NMR experiments and DFT calculations, we investigated the poisoning process of these catalysts by silicon species in order to obtain a better understanding of this process. Two structural models (mono and bilayer) for amorphous silica deposited on the γ-Al2O3 surface and some intermediates that can be formed during this process were proposed. From the calculated 29Si chemical shifts, it was possible to identify chemical shifts variations due to different structural elements for each species, thereby, it was possible to make a more appropriate assignment of the resonances found in 29Si CP/MAS NMR spectra in the literature. Besides that, through of the good agreements obtained between the experimental and simulated 29Si CP/MAS NMR spectra, we identified that probably the D4, T1, T3, T4, Q1 and Q2 species are present in the initial stage of the contamination and that the amorphous silica bilayer model deposited on the γ-Al2O3 surface best characterizes the final stage of the contamination. Moreover, the thermodynamic analysis revealed that the chemisorption reaction of the Hexamethylcyclotrisiloxane (D3) compound is much more stable than the Octamethylcyclotetrasiloxane (D4) compound and of a fragment (corresponding to 13 or 14 of the D3 and D4compounds, respectively), and the chemisorption reaction of the fragment presented the highest values of ΔG°. This leads us to deduce that the D3 and D4 compounds chemisorb preferentially without breaking. Besides, it also showed that the amorphous silica formation process on the γ-Al2O3 surface is spontaneous and the bilayer formation reaction is more stable than the monolayer.

Ripples, Wrinkles, and Crumples in Folded Graphene

Separation of two-dimensional thin-film-materials into single layers had been considered very challenging both theoretically and experimentally until the mechanical exfoliation method was discovered. After the successful separation of single- and/or few-layer graphene, the possibility of wrinkle formation has been one of the main open topics because they were not readily observed in experiments. Here, we report experimental observations of different kinds of repetitive nanoscale deformations (ripples, wrinkles, and crumples) in folded single-layer graphene (SLG) on an SiO2 substrate. Using high-vacuum atomic force microscopy, we observed that SLG that was pre-transferred onto an SiO2 substrate was accidentally folded multiple times during the tip-scanning, resulting in the formation of bilayer and trilayer graphene (TLG). Through high-resolution tapping-mode scanning, we could observe the wrinkles, ripples, and crumples in TLG. Additionally, we observed a herringbone pattern that was attributed to an intermediate stage between the wrinkles and ripples; this intermediate state was labeled as wrinklon structure. In our analysis, to characterize the ripples, wrinkles, and crumples, we measured the spatial repetition and amplitude of each pattern using their average line profile and compared them.

Stability and characterization studies of Span 80 niosomes modified with CTAB in the presence of NaCl

This work reports the study of surface and aggregation properties of formulations containing mixed niosomes of the non-ionic surfactant sorbitan monooleate (Span 80) and the cationic surfactant cetyltrimethylammonium bromide (CTAB), in concentrations of 20 and 4 mol/m3, respectively, in salt-free water and in the presence of NaCl (20, 50 and 80 mol/m3). The aim of this work was the formulation of stable Span 80 and CTAB mixed niosomes with low surfactant concentration. The mixed niosomes were prepared by ultrasonication and their properties (surface tension, particle size distribution, ζ-potential, stability over time and morphology) were measured using different techniques. Data were analyzed and compared with those of the individual surfactants. Experimental results show that the addition of salt decreased the critical micelle concentration (CMC) and the surface tension of the surfactant dispersions with relation to their free-salt formulations. The presence of CTAB in the mixed niosome bilayer decreased the particle size and increased the stability of the mixed niosomes in all the formulations studied, compared with those of single Span 80. Synergism between both surfactants was obtained in the formation of niosome bilayers for formulations in pure water and with 20 and 50 mol/m3 of salt, while antagonism was observed in that of 80 mol/m3 NaCl. These results may allow the use of CTAB adsorbed on mixed niosomes in industrial applications, taking advantage of its antiseptic and antibacterial properties and solving the limitation imposed by its high Krafft temperature.

Sorption-desorption mechanisms and environmental friendliness of different surfactants in enhancing remediation of soil contaminated with polycyclic aromatic hydrocarbons

The ionic and nonionic surfactants have different adsorption-desorption models for polycyclic aromatic hydrocarbons (PAHs) in soil-water system, due to the difference in the composition and charge of the hydrophilic groups. Surfactant eluents retained in the soil may also have a secondary effect on the soil environment. Thus, the aim of the study was to investigate sorption-desorption mechanisms and environmental toxicity of different surfactants in enhancing remediation of soil contaminated with PAHs. The distribution of PAHs between different surfactants and soil is influenced by the surfactant bilayer formation. The average molecular density, Sips isotherm, critical micelle concentration (CMC), and critical washing concentration (CWC) models were used to explore the mechanisms involved in the adsorption-desorption of cationic (cetyltrialkylammonium bromide, CTAB), anionic (sodium dodecyl benzene sulfonate, SDBS), and nonionic (TritonX-100, TX100) surfactants. These models were associated with the surfactant-enhanced remediation (SER) of naphthalene-contaminated soil. The mean concentrations and activity of indigenous bacteria were used to detect the toxic effect of the above surfactants on soil environment. The results of SER experiments showed that there are critical washing points (SDBS = 2.4 CMC, TX100 = 4.6 CMC, CTAB = 3.3 CMC) for different surfactants washing naphthalene (Nap). The values of CWC corresponding to critical washing points were key variables driving the need for added surfactants to remove or immobilize Nap. The CWC of different surfactants could be conveniently predicted by a model based on the surfactant-derived organic carbon. In addition, the mean concentration of viable bacteria in biological culture experiment was highest for TX100, followed by CTAB and SDBS. This study revealed the effects of average molecular density and surfactant-derived organic carbon on the distribution of Nap, and suggested a model for calculating CWC of different surfactants, to optimize SER technology. Biological culture experiment indicated that the high concentration and ionic surfactants had a significantly toxic effect on indigenous bacteria.

Formation and Properties of a Self-Assembled Nanoparticle-Supported Lipid Bilayer Probed through Molecular Dynamics Simulations.

We have carried out coarse-grained molecular dynamics (MD) simulations to study the self-assembly procedure of a system of randomly placed lipid molecules, water beads, and a nanoparticle (NP). The self-assembly results in the formation of the nanoparticle-supported lipid bilayer (NPSLBL), with the self-assembly mechanism being driven by events such as the formation of small lipid clusters, merging of the lipid clusters in the vicinity of the NP to form NP-embedded vesicle with a pore, and collapsing of that pore to eventually form the equilibrated NPSLBL system overcoming a large free-energy barrier. Subsequently, we quantify the properties and the configurations of this NPSLBL system. We reveal that unlike our proposition of an equal number of lipid molecules occupying the inner and outer leaflets in a recent report studying the properties of a preassembled lipid bilayer, the equilibrated self-assembled NPSLBL system demonstrates a much larger number of lipid molecules occupying the outer leaflet as compared to the inner leaflet. Second, the thickness of the water layer entrapped between the NP and the inner leaflet shows similar values as predicted by experiments and our previous study. Finally, we reveal that, similar to our previous study, the diffusivity of the lipid molecules in the outer leaflet is larger than that in the inner leaflet but, due to higher temperature employed during our simulations, are even larger than that predicted by our previous study.

Lipids Lay Thyselves Down: Redox-Induced Lipid Vesicle Fusion Onto Ferrocene-Terminated Self-Assembled Monolayers

Due to the attractive electrochemical properties of ferrocene (fast electron transfer, low oxidation potential, and two stable redox states), ferrocenylalkanethiolates on gold are the most studied and employed electroactive self-assembled monolayer (SAM) system. Oxidation of the SAM-confined ferrocenes to ferroceniums is accompanied by the formation of ion-pairs with counter-ions in solution [1,2]. Ferrocene-terminated SAMs exhibit a reversible electrochemistry in the presence of anionic surfactants such as n-alkyl sulfates and sulfonates, while the less chaotropic n-alkyl phosphates and carboxylates lead to the irreversible oxidation of the SAM-confined ferrocene (Fig. A) [3]. Cyclic voltammetry indicates that these latter surfactants form strong ion pairs with the oxidized ferroceniums; an oxidation peak is observed for the first anodic potential sweep but no reduction peak is detected during the reverse sweep. No redox peaks are observed in subsequent sweeps. The surface plasmon resonance signal does not return back to its original value during reduction, indicating an irreversible adsorption of material to the surface, which in turn suggests the formation of a stable and insoluble ferrocenium-surfactant anion complex or deposit that blocks the redox process. In this work, atomic force microscopy is used to investigate the association of sodium n-dodecanoate to the SAM surface. This electrochemical approach appears to be an effective strategy for triggering the formation of solid-supported lipid membranes by the fusion of phospholipid vesicles onto the ferrocenylalkanethiolate SAM. In fact, phospholipids are double-tailed amphiphiles and these can associate with the oxidized ferrocene (Fig. B). A potential-step hold at 0,64 V for only five minutes induces the immediate adsorption of phosphatidylserine (DMPS, POPS and DOPS) at the SAM-gold/electrolyte interface with a full surface coverage. This technique is a versatile tool that offers many benefits such as, a faster supported lipid bilayers formation mimicking the biological membranes, a larger variety of lipid composition, structure and chemical nature, and a possibility of using metal surfaces considering their potential applications in electrochemical techniques, spectroscopic techniques and surface plasmon resonance. In this work, AFM-based nano-shaving, force spectroscopy, and surface plasmon resonance are combined to determine the thickness of the obtained lipid membrane.

Rapid lipid bilayer membrane formation on Parylene coated apertures to perform ion channel analyses

We present a chip design allowing rapid and robust lipid bilayer (LBL) membrane formation using a Parylene coated thin silicon nitride aperture. After bilayer formation, single membrane channels can be reconstituted and characterized by electrophysiology. The ability for robust reconstitution will allow parallelization and enhanced screening of small molecule drugs acting on or permeating across the membrane channel. The aperture was realized on a microfabricated silicon nitride membrane by using standard clean-room fabrication processes. To ensure the lipid bilayer formation, the nitride membrane was coated with a hydrophobic and biocompatible Parylene layer. We tested both Parylene-C and Parylene-AF4. The contact angle measurements on both Parylene types showed very good hydrophobic properties and affinity to lipids. No precoating of the Parylene with an organic solvent is needed to make the aperture lipophilic, in contradiction to Teflon membranes. The chips can be easily placed in an array utilizing a 3D printed platform. Experiments show repetitive LBL formation and destruction (more than 6 times) within a very short time (few seconds). Through measurements we have established that the LBL layers are very thin. This allows the investigation of the fusion process of membrane proteins i.e. outer membrane protein (OmpF) in the LBL within a few minutes.

Self-Assembly Properties of Solution Processable, Electroactive Alkoxy, and Alkylthienylene Derivatives of Fused Benzoacridines: A Scanning Tunneling Microscopy Study.

Self-organization in mono- and bilayers on HOPG of two groups of benz[5,6]acridino[2,1,9,8-klmna]acridine derivatives, namely, 8,16-dialkoxybenzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridines with an increasing alkoxy substituent length and 8,16-bis(3- or 4- or 5-octylthiophen-2-yl)benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridines, i.e., three positional isomers of the same benzoacridine, is investigated by scanning tunneling microscopy. The layers were deposited from a solution of the adsorbate (in hexane or dichloromethane) and imaged ex situ at molecular resolution. In all cases, the resulting two-dimensional (2D) supramolecular organization is governed by the interactions between large, fused heteroaromatic cores that form densely packed rows separated by areas covered by substituents. In 8,16-dialkoxybenzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridines, the alkoxy substituents, separating the rows of densely packed cores, are interdigitated. An increasing substituent length leads to an intuitively expected increase in this 2D unit cell parameter that corresponds to the orientation of the substituent in the monolayer. In the case of 8,16-bis(3- or 4- or 5-octylthiophen-2-yl)benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine positional isomers, the self-assembly processes are more complex. Although the determined 2D unit cell is in all cases essentially the same, the role of alkylthienylene substituents in layer formation is distinctly different. Thus, the formation of monolayers and bilayers is very sensitive to isomerism. 8,16-Bis(5-octylthiophen-2-yl)benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine is capable of forming the most stable monolayer and the most labile bilayer. In the case of 8,16-bis(3-octylthiophen-2-yl)benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine, an inverse phenomenon is observed leading to the most labile monolayer and the most stable bilayer. These differences are rationalized in terms of dissimilar molecular geometries of the studied isomers and different interdigitation patterns in their 2D supramolecular structures.

Supported Lipid Bilayer Formation from Phospholipid-Fatty Acid Bicellar Mixtures.

Supported lipid bilayers (SLBs) are versatile cell membrane-mimicking biointerfaces for various applications such as biosensors and drug delivery systems, and there is broad interest in developing simple, cost-effective methods to achieve SLB fabrication. One promising approach involves the deposition of quasi-two-dimensional bicelle nanostructures that are composed of long-chain phospholipids and either short-chain phospholipids or detergent molecules. While a variety of long-chain phospholipids have been used to prepare bicelles for SLB fabrication applications, only two short-chain phospholipids, 1,2-dihexanoyl-sn-glycero-3-phosphocholine and 1,2-diheptanoyl-sn-glycero-3-phosphocholine (collectively referred to as DHPC), have been investigated. There remains an outstanding need to identify natural alternatives to DHPC, especially ones that are more affordable, to improve fabrication prospects and application opportunities. Herein, we explored the potential to fabricate SLBs from bicellar mixtures composed of long-chain phospholipids and lauric acid (LA), which is a low-cost, naturally abundant fatty acid that is widely used in soapmaking and various industrial applications. Quartz crystal microbalance-dissipation (QCM-D) experiments were conducted to track bicelle adsorption onto silica surfaces as a function of bicelle composition and lipid concentration, along with time-lapse fluorescence microscopy imaging and fluorescence recovery after photobleaching (FRAP) experiments to further characterize lipid adlayer properties. The results identified optimal conditions where it is possible to efficiently form SLBs from LA-containing bicelles at low lipid concentrations while also unraveling mechanistic insights into the bicelle-mediated SLB formation process and verifying that LA-containing bicelles are biocompatible with human cells for surface coating applications.

Supported Planar Single and Multiple Bilayer Formation by DOPC Vesicle Rupture on Mica Substrate: A Mechanism as Revealed by Atomic Force Microscopy Study

A planar lipid bilayer on a solid support serves as model system that explains fundamental aspects of membrane biology and enables us to characterize wide-range surface-sensitive techniques, including molecular engineering. The present study aims at understanding the process of single and multiple bilayer formation after the exposure of small unilamellar vesicles (SUVs) of dioleoyl phosphatidylcholine (DOPC) to mica substrate. Isolated single bilayer formation and co-existence of double and triple lipid bilayers in the aqueous medium have been quantitatively measured by atomic force microscopy and discussed the physicochemical mechanism. It has been observed that due to the strong adhesion of DOPC SUV to mica surface, vesicles of diluted solution rupture spontaneously and form isolated bilayer patches when they come in contact with the mica surface. No further lateral growth or movement of the bilayer patches has been observed upon increase of incubation time. However, the increase of vesicle number on the same surface area by successive deposition of DOPC solution of same concentration and increasing incubation time shows merging of the nearby patches as well as development of stacked second and third bilayers due to edge-guided rupture of adsorbed vesicles on first or second bilayer patches. Mechanisms of single and multi-bilayer formation and a theoretical interpretation of the process have been elucidated.

Stimulations Inducing Tethered Lipid Bilayer Formation on Protein-Modified Substrate

Stimulations Inducing Tethered Lipid Bilayer Formation on Protein-Modified Substrate

Hybrid Lipid-Polymer Bilayers: pH-Mediated Interactions between Hybrid Vesicles and Glass.

One practical approach towards robust and stable biomimetic platforms is to generate hybrid bilayers that incorporate both lipids and block co-polymer amphiphiles. The currently limited number of reports on the interaction of glass surfaces with hybrid lipid and polymer vesicles—DOPC mixed with amphiphilic poly(ethylene oxide-b-butadiene) (PEO-PBd)—describe substantially different conclusions under very similar conditions (i.e., same pH). In this study, we varied vesicle composition and solution pH in order to generate a broader picture of spontaneous hybrid lipid/polymer vesicle interactions with rigid supports. Using quartz crystal microbalance with dissipation (QCM-D), we followed the interaction of hybrid lipid-polymer vesicles with borosilicate glass as a function of pH. We found pH-dependent adsorption/fusion of hybrid vesicles that accounts for some of the contradictory results observed in previous studies. Our results show that the formation of hybrid lipid-polymer bilayers is highly pH dependent and indicate that the interaction between glass surfaces and hybrid DOPC/PEO-PBd can be tuned with pH.

Development and Validation of a Two-Stage Kinetic Sorption Model for Polymer and Surfactant Transport in Porous Media.

Understanding the sorption processes is critical to the successful design and implementation of a variety of technologies in subsurface application. Most transport models assume minimal interactions between adsorbed species and, thus, are unable to accurately describe the formation of adsorbed bilayers. To address this limitation, a two-stage kinetic sorption model is developed and incorporated into a one-dimensional advective-dispersive-reactive transport simulator. The model is evaluated using data obtained from column experiments conducted with a representative polymer [gum arabic (GA)] and a nonionic surfactant [Witconol 2722 (WT)] under a range of experimental conditions. Model simulations demonstrate that the first-stage polymer/surfactant-surface sorption rate is at least 1 order of magnitude greater than the second-stage rate, associated with bilayer formation, indicating that the first-stage reaction is more favorable. The reversibility of the second-stage sorption process is found to be compound-specific, with irreversible sorption observed for GA and prolonged tailing observed for WT. This study demonstrates that the developed two-stage kinetic model is superior to a two-stage equilibrium-based model in its replication of two-leg breakthrough curves observed in core flood experiments; the normalized root-mean-square error between measurement and regressed model simulations was reduced by an average of 41% with the kinetic approach.

Adsorption of O and Cl on Tl/Si(111)––Suppressed spin polarization via bilayer formation

Adsorption of O and Cl on Tl/Si(111) is studied using density functional theory. The surface of the Cl-Tl/Si(111) system was found to be metallic while that for O-Tl/Si(111), semiconducting. It is found, however, that the O/Tl and Cl/Tl interactions in Tl/Si(111) are very similar in nature and lead to the formation of the Tl-O and Tl-Cl bilayers weakly bonded to the Si(111)-1 × 1 substrate. The spin polarization of the Tl-induced gap states, originally present in Tl/Si(111), is also suppressed in both systems.

Proximity Spin–Orbit Torque on a Two-Dimensional Magnet within van der Waals Heterostructure: Current-Driven Antiferromagnet-to-Ferromagnet Reversible Nonequilibrium Phase Transition in Bilayer CrI3

The recently discovered two-dimensional magnetic insulator CrI3 is an intriguing case for basic research and spintronic applications since it is a ferromagnet in the bulk, but an antiferromagnet in bilayer form, with its magnetic ordering amenable to external manipulations. Using first-principles quantum transport approach, we predict that injecting unpolarized charge current parallel to the interface of bilayer-CrI3monolayer-TaSe2 van der Waals heterostructure will induce spin-orbit torque and thereby driven dynamics of magnetization on the first monolayer of CrI3 in direct contact with TaSe2. By combining calculated complex angular dependence of spin-orbit torque with the Landau-Lifshitz-Gilbert equation for classical dynamics of magnetization, we demonstrate that current pulses can switch the direction of magnetization on the first monolayer to become parallel to that of the second monolayer, thereby converting CrI3 from antiferromagnet to ferromagnet while not requiring any external magnetic field. We explain the mechanism of this reversible current-driven nonequilibrium phase transition by showing that first monolayer of CrI3 carries current due to evanescent wavefunctions injected by metallic transition metal dichalcogenide TaSe2, while concurrently acquiring strong spin-orbit coupling via such proximity effect, whereas the second monolayer of CrI3 remains insulating. The transition can be detected by passing vertical read current through the vdW heterostructure, encapsulated by bilayer of hexagonal boron nitride and sandwiched between graphite electrodes, where we find tunneling magnetoresistance of ∼240%.

Simultaneous measurement of surface and bilayer tension in a microfluidic chip.

Freestanding lipid bilayers are one of the most used model systems to mimic biological cell membranes. To form an unsupported bilayer, we employ two aqueous fingers in a microfluidic chip surrounded by an oily phase that contains lipids. Upon pushing two aqueous fingers forward, their interface becomes decorated with a lipid monolayer and eventually zip to form a bilayer when the monolayers have nanoscopic contact with each other. Using this straightforward approach, the quick and easy bilayer formation is facilitated by oil draining into the microfluidic device material consisting of polydimethylsiloxane. However, the oil drainage limits the lifetime of a bilayer to about 1 h. We demonstrate that this drainage can be managed, resulting in superior bilayer stability and an increased lifetime of several hours when using a pressure-controlled system. Applying different pressures to the aqueous fingers in the microfluidic chip, the formed bilayer can even be bent to a desired curvature. Extracting the contact angle and the resulting curvature of the bilayer region, for a given applied pressure difference, both the bilayer tension and the surface tension of each lipid monolayer can be derived from a single experiment using the Young Laplace pressure equation.

Gasochromic response of optical sensing platform integrated with polyaniline and poly(3,4-ethylenedioxythiophene) exposed to NH3 gas

The optical NH3 gas sensing performance of polyaniline (PANI) and poly(3,4-ethylenedioxythiophene (PEDOT) in the form of bilayers and copolymers was analysed in this study. The order of the bilayers and the presence of acid dopant on the fabrication of the sensing platform produced different absorbance responses upon exposure to NH3 gas. The limit of detection of the bilayer (PANI(aq.)/PEDOT(aq.)) was 7.86 ppm which is under the threshold limit value of NH3, with response and recovery times of 2.33 min and 46.8 s, respectively. The gasochromic behaviour of PANI and PEDOT during the adsorption of NH3 gas was closely related to the changes in the oxidation state which have simultaneously altered the colour intensity of the respective sensing layer.