Layer Of Vesicles Research Articles

The heat-transfer method: a versatile low-cost, label-free, fast, and user-friendly readout platform for biosensor applications.

In recent years, biosensors have become increasingly important in various scientific domains including medicine, biology, and pharmacology, resulting in an increased demand for fast and effective readout techniques. In this Spotlight on Applications, we report on the recently developed heat-transfer method (HTM) and illustrate the use of the technique by zooming in on four established bio(mimetic) sensor applications: (i) mutation analysis in DNA sequences, (ii) cancer cell identification through surface-imprinted polymers, (iii) detection of neurotransmitters with molecularly imprinted polymers, and (iv) phase-transition analysis in lipid vesicle layers. The methodology is based on changes in heat-transfer resistance at a functionalized solid-liquid interface. To this extent, the device applies a temperature gradient over this interface and monitors the temperature underneath and above the functionalized chip in time. The heat-transfer resistance can be obtained by dividing this temperature gradient by the power needed to achieve a programmed temperature. The low-cost, fast, label-free and user-friendly nature of the technology in combination with a high degree of specificity, selectivity, and sensitivity makes HTM a promising sensor technology.

Evidence from mathematical modeling that carbonic anhydrase II and IV enhance CO2 fluxes across Xenopus oocyte plasma membranes.

Exposing an oocyte to CO2/HCO3 (-) causes intracellular pH (pHi) to decline and extracellular-surface pH (pHS) to rise to a peak and decay. The two companion papers showed that oocytes injected with cytosolic carbonic anhydrase II (CA II) or expressing surface CA IV exhibit increased maximal rate of pHi change (dpHi/dt)max, increased maximal pHS changes (ΔpHS), and decreased time constants for pHi decline and pHS decay. Here we investigate these results using refinements of an earlier mathematical model of CO2 influx into a spherical cell. Refinements include 1) reduced cytosolic water content, 2) reduced cytosolic diffusion constants, 3) refined CA II activity, 4) layer of intracellular vesicles, 5) reduced membrane CO2 permeability, 6) microvilli, 7) refined CA IV activity, 8) a vitelline membrane, and 9) a new simulation protocol for delivering and removing the bulk extracellular CO2/HCO3 (-) solution. We show how these features affect the simulated pHi and pHS transients and use the refined model with the experimental data for 1.5% CO2/10 mM HCO3 (-) (pHo = 7.5) to find parameter values that approximate ΔpHS, the time to peak pHS, the time delay to the start of the pHi change, (dpHi/dt)max, and the change in steady-state pHi. We validate the revised model against data collected as we vary levels of CO2/HCO3 (-) or of extracellular HEPES buffer. The model confirms the hypothesis that CA II and CA IV enhance transmembrane CO2 fluxes by maximizing CO2 gradients across the plasma membrane, and it predicts that the pH effects of simultaneously implementing intracellular and extracellular-surface CA are supra-additive.

Phase transitions in lipid vesicles detected by a complementary set of methods: heat‐transfer measurements, adiabatic scanning calorimetry, and dissipation‐mode quartz crystal microbalance

We report on the use of the heat transfer method, a novel surface‐sensitive technique based on heat transfer through solid–liquid interfaces, to detect phase transitions of model lipid membranes. We selected the lipid DPPC because of its rich phase behavior in an experimentally accessible temperature range. The vesicles were adsorbed on nanocrystalline diamond films, known as a versatile platform material for biosensing with outstanding heat‐conduction properties. Complementary Peltier‐element‐based adiabatic scanning calorimetry (pASC) and quartz crystal microbalance with dissipation monitoring (QCM‐D) measurements were carried out to monitor the phase transitions in multilamellar and small unilamellar vesicles, respectively. The heat‐transfer measurements revealed reversible jumps upon heating and cooling in the thermal resistance in the vicinity of the expected transition temperature and they agree qualitatively with molecular simulations of the thermal conductivity across a lipid bilayer. The results show the capability of the heat transfer method to detect the main phase transition in DPPC, opening new perspectives for the study of more complex lipid systems and different solid platforms. This work confirms QCM‐D as a useful tool for the assessment of the structural changes upon the phase conversion and shows the capability of pASC to provide high‐resolution thermodynamic information on biophysical systems.Temperature profile of the heat transfer resistance Rth during the main phase transition of a DPPC supported vesicle layer adsorbed on a hydrogen‐terminated nanocrystalline diamond substrate. The arrows indicate the sense of the run: heating (red solid line) and cooling (blue solid line).

Spherical Blackberry-type Capsules Containing Block Copolymer Aggregates

The design, preparation, and properties of nanosized blackberry-like structures are described. These capsules are composed of two layers of individual block copolymer aggregates, relatively large core vesicles onto which is deposited a layer of smaller vesicles or micelles. The composition of the adjacent layers is such as to ensure strong electrostatic interactions between them. The core vesicles are typically composed of either PS-b-P4VP with a positively charged corona or of PS-b-PAA with a negatively charged corona, and are surrounded by a layer of smaller, oppositely charged block copolymer vesicles or micelles. These composite structures bear a strong resemblance to blackberries, hence the proposed name. The blackberry structures can be prepared in solution or on a flat surface, for example, a silicon wafer. Four compositional possibilities for the blackberries structures were studied, in which the positively or negatively charged core vesicles are covered either by a layer of oppositely charged micelles or by vesicles. These structures represent the earliest stage of a layer-by-layer approach of small spherical aggregates onto a larger spherical hollow core. The strong interaction between the contacting layers is achieved by electrostatic interactions or by complementary acid-base properties, for example, H-bonding. These multicompartmented capsules could be used potentially as delivery vehicles for multiple components; each layer of the capsules could be loaded with hydrophobic (in the core of the micelles or vesicle wall) or hydrophilic molecules (in the vesicle cavity). The overall size of such structures can vary, but in any case can be kept below 1 μm.

Ultrastructural Characteristics of Spermiogenesis inRhynchophorus ferrugineus(Coleoptera: Curculionidae)

Abstract The red palm weevil (RPW), Rhynchophorus ferrugineus Olivier (Coleoptera: Curculionidae), is a pest that is rapidly spreading across the globe. Here, the ultrastructure of R. ferrugineus spermatogenesis and sperm are described. The histology of the testis, sperm ultrastructure, and spermiogenesis were investigated using light and transmission electron microscopy. The differentiation of spermatids was observed to occur within spermiogenetic cysts. Inside each cyst, the spermatids were at the same stage of maturation. During early stages, mitochondria aggregated, fused, and elongated beside the growing flagellar axoneme, while the proacrosome transformed into a triple-layered acrosome, with a perforatorium, acrosomal vesicle, and extra-acrosomal layer. The centriolar adjunct was present in early spermatids but was absent from later spermatid stages and sperm. The sperm's tail displayed a typical axoneme with a 9 + 9 + 2 microtubule arrangement, 2 mitochondrial derivatives of unequal size, and 2 acc...

A polysiloxane surfactant dissolves a poorly soluble drug (nystatin) in water

The aqueous dissolution of a poorly soluble drug nystatin (Nys) was achieved by a simple, excipient-free procedure using a tromethamol-modified polysiloxane (ST) as surfactant. Long-term stable Nys aqueous formulation was prepared and investigated by different methods, in order to understand the mechanism of drug solubilization. The cryo-TEM analysis revealed the presence of soft vesicles in the Nyst_ST solution. According to TEM measurements, the drug is contained in the hydrophobic layer of the surfactant vesicles. The dynamic light scattering (DLS) measurements on Nys_ST showed a main population around 134nm having the Zeta potential of 33.3mV. FT-IR, UV–vis, and thermogravimetric (TG-DTG-DTA) data point toward physical encapsulation, accompanied by a decrease of H-bonding between the drug molecules. The antifungal activity tested in vitro toward four yeast strains was seriously improved compared to the aqueous dispersion of the native drug, although the availability was diminished compared to DMSO solution.

Pluronic-Based Core/Shell Nanoparticles for Drug Delivery and Diagnosis

Pluronic-based core/shell nanoparticles (NPs) were formed using various strategies such as self-assembly and temperature induced-phase transition. To improve their functionality as a nanomedicine for diagnosis and therapy, the vesicle fusion and layer by layer approach were employed. Because of the hydrophilic nature of the Pluronic shell and the relatively small size, Pluronic-based core/shell NPs were used in order to improve their pharmacokinetic behaviors in drugs and in imaging agents. This review will introduce various types of Pluronic-based core/shell NPs according to their preparation method and formation mechanism. The focus will be on the Pluronic-based core/shell NPs for tumor targeting, stimulated release of proteins, and cancer imaging capabilities.

Layer-by-Layer Deposition of Vesicles Mediated by Supramolecular Interactions

Vesicles are dynamic supramolecular structures with a bilayer membrane consisting of lipids or synthetic amphiphiles enclosing an aqueous compartment. Lipid vesicles have often been considered as mimics for biological cells. In this paper, we present a novel strategy for the preparation of three-dimensional multilayered structures in which vesicles containing amphiphilic β-cyclodextrin are interconnected by proteins using cyclodextrin guests as bifunctional linker molecules. We compared two pairs of adhesion molecules for the immobilization of vesicles: mannose-concanavalin A and biotin-streptavidin. Microcontact printing and thiol-ene click chemistry were used to prepare suitable substrates for the vesicles. Successful immobilization of intact vesicles through the mannose-concanavalin A and biotin-streptavidin motifs was verified by fluorescence microscopy imaging and dynamic light scattering, while the vesicle adlayer was characterized by quartz crystal microbalance with dissipation monitoring. In the case of the biotin-streptavidin motif, up to six layers of intact vesicles could be immobilized in a layer-by-layer fashion using supramolecular interactions. The construction of vesicle multilayers guided by noncovalent vesicle-vesicle junctions can be taken as a minimal model for artificial biological tissue.

Sodium selective ion channel formation in living cell membranes by polyamidoamine dendrimer

Polyamidoamine (PAMAM) dendrimers are highly charged hyperbranched protein-like polymers that are known to interact with cell membranes. In order to disclose the mechanisms of dendrimer–membrane interaction, we monitored the effect of PAMAM generation five (G5) dendrimer on the membrane permeability of living neuronal cells followed by exploring the underlying structural changes with infrared-visible sum frequency vibrational spectroscopy (SVFS), small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). G5 dendrimers were demonstrated to irreversibly increase the membrane permeability of neurons that could be blocked in low-[Na+], but not in low-[Ca2+] media suggesting the formation of specific Na+ permeable channels. SFVS measurements on silica supported DPPG–DPPC bilayers suggested G5-specific trans-polarization of the membrane. SAXS data and freeze-fracture TEM imaging of self-organized DPPC vesicle systems demonstrated disruption of DPPC vesicle layers by G5 through polar interactions between G5 terminal amino groups and the anionic head groups of DPPC. We propose a nanoscale mechanism by which G5 incorporates into the membrane through multiple polar interactions that disrupt proximate membrane bilayer and shape a unique hydrophilic Na+ ion permeable channel around the dendrimer. In addition, we tested whether these artificial Na+ channels can be exploited as antibiotic tools. We showed that G5 quickly arrest the growth of resistant bacterial strains below 10μg/ml concentration, while they show no detrimental effect on red blood cell viability, offering the chance for the development of new generation anti-resistant antibiotics.

Adsorption, Organization, and Rheology of Catanionic Layers at the Air/Water Interface

We have investigated the adsorption and organization at the air/water interface of catanionic molecules released from a dispersion of solid-like catanionic vesicles composed of myristic acid and cetyl trimethylammonium chloride at the 2:1 ratio. These vesicles were shown recently to be promising foam stabilizers. Using Brewster angle microscopy, we observed the formation of a catanionic monolayer at the air/water interface composed of liquid-condensed domains in a liquid-expanded matrix. Further adsorption of catanionic molecules forced them to pack, thereby forming a very dense monolayer that prevented further vesicle rupture by avoiding contact of the vesicles with air. Moreover, confocal fluorescence microscopy revealed the presence of layers of intact vesicles that were progressively creaming toward this catanionic monolayer; the surface tension of the vesicle dispersion remained constant upon creaming. The catanionic monolayer behaved as a soft glassy material, an amorphous solid with time- and temperature-dependent properties. Using interfacial oscillatory rheology, we found that the monolayer relaxed mechanical stresses in seconds and melted at a temperature very close to the melting transition temperature of the vesicle bilayers. These results have potential application in the design of smart foams that have temperature-tunable stability.

Control over the color transition behavior of polydiacetylene vesicles using different alcohols

In this contribution, we investigate the color transition behavior of polydiacetylene (PDA) vesicles upon exposure to different chemical stimuli. A series of linear and branched alcohols are used as model additives, allowing systematic control of their molecular shape and polarity. The PDA vesicles are fabricated by using three monomers, 10,12-pentacosadiynoic acid (PCDA), 10,12-tricosadyinoic acid (TCDA), and N-(2-amino ethyl)pentacosa-10,12-dyinamide (AEPCDA). When a series of linear alcohols is used, the longer alcohol length causes color transition of all PDA vesicles. In this system, the penetration of linear alcohols into the inner layer of PDA vesicles is dictated by their polarity. The change of –OH position within the alcohol molecule also affects the degree of penetration. It requires a higher amount of the 2-propanol to induce color transitions of the PDAs compared to that of the 1-propanol. The addition of methyl branches into the hydrophobic tail of alcohols causes an increase in steric effect, which hinders the penetration as well. When the 2,2-dimethyl-1-propanol is used as a stimulus, the color transition of PDAs occurs at much higher alcohol concentration compared to 2-methyl-1-butanol, 3-methyl-1-butanol, and 1-pentanol. The variation of PDA structures also affects their ability to interact with the alcohols. The modified head group of poly(AEPCDA) promotes the ability to distinguish between 1-propanol and 2-propanol or 1-propanol and ethanol.

A general template for synthesis of hollow microsphere with well‐defined structure

AbstractUsing chitooligosaccharides (COS) as the backbones and polycaprolactones (PCL) as the branches, a novel type of amphiphilic graft copolymers with a large amount of free OH and NH2 groups remained on the COS backbones was synthesized. The obtained Chitooligosaccharide‐graft‐poly(ε‐caprolactone)(COS‐g‐PCL) was self‐assembled into giant vesicles which served as templates for the preparation of hollow spheres of a series of metals(Au, Ag, Cu, Pt, and Pd). The method involved the initial mixing of COS‐g‐PCL and metal‐containing groups or metal ions to generate corresponding complex, followed by adding the selective solvent of water to induce the self‐assembly of the graft copolymers into giant vesicles; Metal ions were reduced and crosslinked by a subsequent calcination procedure to form metal hollow spheres. In addition, hybrid hollow spheres with fluorescent quantum dots and silica hollow spheres were also prepared by slightly modified procedures. A preliminary study on the trinitrotoluene sensor of CdS/vesicle hybrid hollow spheres revealed a considerable sensitivity, which exemplifies the distinct properties imparted by the hybrid hollow structure. All of the results demonstrate that the giant vesicles self‐assembled from COS‐g‐PCL could be utilized as effective templates for the synthesis of various hollow spheres. Using Chitooligosaccharide‐graft‐poly(ε‐caprolactone) vesicles as general templates, the hollow spheres of a series of metals such as Au, Ag, Cu, and Pt were produced. The method involved the initial absorption of metal ions from solution into the functional surface layer of the graft copolymer giant vesicles. Metal ions were reduced and crosslinked by a subsequent calcination procedure to form metal hollow spheres. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Solubilization of saikosaponin a by ginsenoside Ro biosurfactant in aqueous solution: Mesoscopic simulation

Ginsenoside Ro (Ro), a natural anionic biosurfactant derived from ginseng, has been found to markedly increase the solubility of saikosaponin a (SSa), which is the active ingredient of Radix Bupleuri. SSa is minimally soluble in water. To determine the mechanism by which Ro solubilizes SSa, the self-assembly behavior of Ro and the phase behavior of blended Ro and SSa systems were studied by mesoscopic dynamics (MesoDyn) and dissipative particle dynamics (DPD) simulations. The simulation results show that Ro can form vesicles via the closure of oblate membranes. At low concentrations, SSa molecules are solubilized in the palisade layer of the Ro vesicles. At high concentrations, they interact with Ro molecules to form mixed vesicles with Ro adsorbing on the surfaces of the vesicles. The evaluation of the SSa solubilization process reveals that, at low concentrations, Ro aggregates preferentially to form vesicles, which then absorb SSa into themselves. However, at high concentrations, SSa first self-aggregates and then dissolves. This is because the solubilization behavior of Ro shifts the precipitation–dissolution equilibrium in the direction of dissolution. These results of the simulations are consistent with those of transmission electron microscopy (TEM) and dynamic light scattering (DLS).

Characterization of Phospholipid Bilayer Formation on a Thin Film of Porous SiO2 by Reflective Interferometric Fourier Transform Spectroscopy (RIFTS)

Classical methods for characterizing supported artificial phospholipid bilayers include imaging techniques such as atomic force microscopy and fluorescence microscopy. The use in the past decade of surface-sensitive methods such as surface plasmon resonance and ellipsometry, and acoustic sensors such as the quartz crystal microbalance, coupled to the imaging methods, have expanded our understanding of the formation mechanisms of phospholipid bilayers. In the present work, reflective interferometric Fourier transform spectrocopy (RIFTS) is employed to monitor the formation of a planar phospholipid bilayer on an oxidized mesoporous Si (pSiO(2)) thin film. The pSiO(2) substrates are prepared as thin films (3 μm thick) with pore dimensions of a few nanometers in diameter by the electrochemical etching of crystalline silicon, and they are passivated with a thin thermal oxide layer. A thin film of mica is used as a control. Interferometric optical measurements are used to quantify the behavior of the phospholipids at the internal (pores) and external surfaces of the substrates. The optical measurements indicate that vesicles initially adsorb to the pSiO(2) surface as a monolayer, followed by vesicle fusion and conversion to a surface-adsorbed lipid bilayer. The timescale of the process is consistent with prior measurements of vesicle fusion onto mica surfaces. Reflectance spectra calculated using a simple double-layer Fabry-Perot interference model verify the experimental results. The method provides a simple, real-time, nondestructive approach to characterizing the growth and evolution of lipid vesicle layers on the surface of an optical thin film.

Numerical experiment of cyclic layering in a solidified binary eutectic melt

In shallow magmatic intrusions, a characteristic layering structure (hereafter referred to as cyclic layering) can sometimes be observed. This cyclic layering is caused by double diffusion and crystallization kinetics, and different from what is observed as rhythmic layering caused by gravity. The cyclic layering is visualized as differential weathering in response to the differential stiffness caused by textural variations such as those in the volume fraction, number density, and size of vesicles or crystals. The spacing of layers seems to increase according to a geometric progression, like as in Liesegang bands of a diffusion‐precipitation system. In order to understand the development condition for cyclic layering and the characteristics of textural variations, such as the spacing of layering in crystallized multi‐component melts by conductive cooling, we carried out a numerical experiment on the 1D crystallization process of a binary eutectic melt. This simulation took into account the cooling from contact with country rock as well as the compositional and thermal diffusion and the kinetics of diffusion‐limited crystallization. The governing equations include dimensionless control parameters describing the relative importance of thermal diffusion or compositional diffusion (Lewis number, Le) and the effective latent heat release (Stefan number, St). From the results of the numerical experiments, it was found that the layering develops through eutectic oscillation (compositional and thermal oscillation below the eutectic point), suggesting that the bi‐activating condition, whereby both phases cooperatively activate their crystallization rates, is essential for the development of layering. No layering is observed at the margin, and the length of the region with no layering increases exponentially with decreasing St. The amplitude of textural oscillation decreases with decreasing St. Thus, practically no layering develops at small latent heat release. Three types of layering structure or oscillatory profiles of texture are observed (short, long and multiple types), depending mainly on Le. Realistic values of Le and St suggest that natural cyclic layering is the multiple or long type of layering. The common ratios of geometric progressions converge with increasing Le to constants in the range of approximately 1.02–1.05, which is similar to the range of the natural observations. Experiments with no latent heat release by the second‐phase simulating vesicles show similar oscillatory behaviors, suggesting that the latent heat release of the first crystallizing phase is an essential factor for the development of vesicle layering.

Hydration lubrication: exploring a new paradigm

Lubrication by hydration shells that surround, and are firmly attached to, charges in water, and yet are highly fluid, provide a new mode for the extreme reduction of friction in aqueous media. We report new measurements, using a mica surface-force balance, on several different systems which exhibit hydration lubrication, extending earlier studies significantly to shed new light on the nature and limits of this mechanism. These include lubrication by hydrated ions trapped between charged surfaces, and boundary lubrication by surfactants, by polyzwitterionic brushes and by close-packed layers of phosphatidylcholine vesicles. Sliding friction coefficients as low as 10(-4) or even lower, and mean contact pressures of up to 17 MPa or higher are indicated. This suggests that the hydration lubrication mechanism may underlie low-friction sliding in biological systems, in which such pressures are rarely exceeded.

Induced dye leakage by PAMAM G6 does not imply dendrimer entry into vesicle lumen

Dendrimers are polymers with unique properties that make them promising in a variety of applications such as potential drug and gene delivery systems. Polyamidoamine (PAMAM) dendrimers, in particular, have been widely investigated since they enter rapidly into cells. The entry mechanism, however, is still not yet fully clarified as both passive and active uptake have been proposed. In this work we focus on understanding passive uptake, for which simple cell model systems are used in order to ensure that only dendrimer–lipid interactions are probed. We developed protocols for investigating independently the effect of the dendrimer on lipid bilayer integrity, in terms of permeability of small dyes and effective dendrimer translocation. This was achieved by the use of membrane labeled giant unilamellar vesicles (GUVs) either containing Alexa 488 hydrazide in the vesicle lumen or FITC-labeled PAMAM G6 dendrimers. Vesicle integrity and dendrimer–membrane binding were then assessed by fluorescence microscopy. The importance of membrane fluidity and charge was investigated using GUVs composed of various lipid compositions. A quartz crystal microbalance with dissipation was used to probe the effect of dendrimers on the rigidity of vesicle layers. The results indicate that PAMAM dendrimers can locally alter the membrane properties. An increased bilayer permeability towards soluble small dyes but no effective translocation, where PAMAM dendrimers could dissociate from the lipid membrane into the vesicle lumen, was observed. To our knowledge this is the first time it is shown that PAMAM G6 dendrimer does not effectively translocate the lipid bilayer although it readily interacts with the model membrane, regardless of lipid membrane properties. However, bilayer charge and fluidity modulate the dendrimer interaction in agreement with previous reports. The results clearly highlight the importance of the choice of the model system when investigating nanoparticles interaction with lipid membranes.

Supported Lipid Bilayers on Biocompatible Polysaccharide Multilayers

Formation of supported lipid bilayers on soft polymer cushions is a useful approach to decouple the membrane from the substrate for applications involving membrane proteins. We prepared biocompatible polymer cushions by the layer-by-layer assembly of two polysaccharide polyelectrolytes, chitosan (CHI) and hyaluronic acid, on glass and silicon substrates. (CHI/HA)(5) films were characterized by atomic force microscopy, giving an average thickness of 57 nm and roughness of 25 nm in aqueous solution at pH 6.5. Formation of zwitterionic lipid bilayers by the vesicle fusion method was attempted using DOPC vesicles at pH 4 and 6.5 on (CHI/HA)(5) films. At higher pH adsorbed lipids had low mobility and large immobile lipid fractions; a combination of fluorescence and AFM indicated that this was attributable to formation of poor quality membranes with defects and pinned lipids rather than to a layer of surface-adsorbed vesicles. By contrast, more uniform bilayers with mobile lipids were produced at pH 4. Fluorescence recovery after photobleaching gave diffusion coefficients that were similar to those for bilayers on PEG cushions and considerably higher than those measured on other polyelectrolyte films. The results suggest that the polymer surface charge is more important than the surface roughness in controlling formation of mobile supported bilayers. These results demonstrate that polysaccharides provide a useful alternative to other polymer cushions, particularly for applications where biocompatibility is important.

Screening of antimicrobial membrane-active metabolites of soil microfungi by using chromatic phospholipid/polydiacetylene vesicles

The focus of this study is screening of antimicrobial membrane-active metabolites of soil microfungi by using chromatic phospholipid/polydiacetylene vesicles. In this work, soil samples were collected from desert, forest, farm, lake shore and mineral zones of Northern and Central parts of Iran. These parts were not studied for antimicrobial potential of the soil isolates producing metabolites with membrane activity in particular, from microfungi. In the primary screening that was performed to evaluate the antimicrobial activity, isolates were analyzed in terms of their general inhibition effects to indicator strains including Escherichia coli, Candida albicans, and Saccharomyces cerevisiae. In the secondary screening, isolates producing membrane-active metabolites were determined using a Rapid Chromatic Detection method. The chromatic technology is simple and this method provides a rapid and easy evaluation of interactions between antimicrobial membrane-active metabolites and lipid layers of vesicles as well. A total number of 59 species of fungi was isolated from the soil samples. It has been found that 20 isolates were effective against indicator strains. Based on color and fluorescence changes that are easily identified by the naked eye and fluorescent microscopy and can be recorded by UV-Vis spectrophotometery, one fungus showed antimicrobial membrane-activity effect against some of the indicator strains. This isolate was identified to the genus level that belonged to Aspergillus. As resistance is barely developed against membrane-active antibiotics, in this paper, we demonstrated the application of the chromatic vesicle model for screening of antimicrobial membrane-active metabolites as potential new antibiotics from soil microfungi.

Formation of an intact liposome layer adsorbed on oxidized gold confirmed by three complementary techniques: QCM‐D, AFM and confocal fluorescence microscopy

Supported layers of vesicles of dimyristoyl and dipalmitoyl phosphatidylcholine (DMPC and DPPC) containing cholesterol (CHOL) are adequate models for eukaryotic plasma membranes. Among the possible substrates to support these layers, gold offers the possibility of being used as an electrode for application in sensors. However, the formation of intact liposome layers on gold is not completely understood and several authors use more or less complex strategies to bind the liposomes. In this work we investigate the adsorption of unilamellar vesicles of DMPC, DMPC/CHOL and DMPC/DPPC/CHOL on the surface of oxidized gold using a quartz crystal microbalance with dissipation, atomic force microscopy and laser scanning confocal fluorescence microscopy. The results of all techniques indicate that for lipid concentrations ≥ 0.7 mg⋅mL–1 a dense layer of intact liposomes irreversibly adsorbs on the gold surface. Copyright © 2011 John Wiley & Sons, Ltd.