Liposomes: technologies and analytical applications

Response of membrane tension to gravity in an approximate cell model

Background

Gravity, especially hypergravity, can affect the morphology of membranes, and further influence most biological processes. Since vesicle structures are relatively simple, the vesicle can be treated as a vital model to study the mechanical properties of membranes in most cases. Basic research on membrane tension has become a vital research topic in cellular biomechanics.

Methods

In this study, a new vesicle model is proposed to quantitatively investigate the response of membrane tension to gravity. In the model, the aqueous lumen inside the vesicle is represented by water, and the vesicle membrane is simplified as a closed, thin, linear elastic shell. Then, the corresponding static equilibrium differential equations of membrane tension are established, and the analytical expression is obtained by the semi-inverse method. The model parameters of the equations are accurately obtained by fitting the reported data, and the values calculated by the model agree well with the reported results.

Results

The results are as follows: First, both the pseudo-ellipsoidal cap and the pseudo-spherical cap can be used to describe the deformed vesicle model; however, the former can better represent the deformation of the vesicle model because the variance of the pseudo-ellipsoidal cap is smaller. Second, the value of membrane tension is no longer a constant for both models. Interestingly, it varies with the vesicle height under the action of gravity. The closer it is to the substrate, the greater the membrane tension. Finally, the inclination between the tangent and the radial lines at a certain point is nearly proportional to the radius of the cross section in both models.

Conclusion

These findings may be helpful to study the vesicle model spreading more accurately by taking into account the influence of gravity because it could affect the distribution of membrane tension. Furthermore, it may also provide some guidance for cell spreading and may have some implications for membrane tension-related mechanobiology studies, especially in the hypergravity conditions.

How Well Can You Tailor the Charge of Lipid Vesicles?

Knowledge and control of surface charge or potential is important for tailoring colloidal interactions. In this work, we compare widely used zeta potential (ζ) measurements of charged lipid vesicle surface potential to direct measurements using the surface force apparatus (SFA). Our measurements show good agreement between the two techniques. On varying the fraction of anionic lipids dimyristoylphosphatidylserine (DMPS) or dimyristoylphosphatidylglycerol (DMPG) mixed with zwitterionic dimyristoylphosphatidylcholine (DMPC) from 0 to 100 mol % we observed a near-linear increase in membrane surface charge or potential up to 20-30 mol % charged lipids beyond which charge saturation occurred in physiological (high) salt conditions. Similarly, in low salt concentrations, a linear increase in charge/potential was found but only up to ∼5-10 mol % charged lipids beyond which the surface charge or potential leveled off. While a lower degree of ionization is expected due to the lower dielectric constant (ε ∼ 4) of the lipid acyl chain environment, increasing intramembrane electrostatic repulsion between neighboring charged lipid head groups at higher charge loading contributes to charge suppression. Measured potentials in physiological salt solutions were consistent with predictions using the Gouy-Chapman-Stern-Grahame (GCSG) model of the electrical double layer with Langmuir binding of counterions, but in low salt conditions, the model significantly overestimated the surface charge/potential. The much lower ionization in low salt (maximum ∼1-2% of total lipids ionized) instead was consistent with counterion condensation at the bilayer surface which limited the charge that could be obtained. The strong interplay between membrane composition, lipid headgroup ionization, electrolyte concentration, and solution pH complicates exact prediction and tuning of membrane surface charge for applications. However, the theoretical frameworks used here can provide guidelines to understand this interplay and establish a range of achievable potentials for a system and predict the response to triggers like pH and salt concentration changes.

Immunoliposome-based fluorometric patulin assay by using immunomagnetic nanoparticles

A fluorometric immunoassay is described for the determination of patulin, a highly toxic fungal metabolite. A rabbit anti-patulin-bovine serum albumin (BSA) IgG conjugate was prepared and used to compose immunoliposomes and immunomagnetic nanoparticles. The immunomagnetic nanoparticles are then added to the sample to form the patulin-antibody composites which can be magnetically separated. The immunoliposomes are then added to form a sandwich. After magnetic separation of the composites and adding n-octyl-β-D-glucopyranoside, the fluorophore sulforhodamine B (SRB) is released. Its fluorescence intensity was then measured at excitation/emission wavelengths of 550/585 nm. The immunoliposome-based immunomagnetic nanoparticle assay can detect 8 μg L⁻¹ of patulin in apple juice without the need for extraction, separation, and purification. The detection limit falls within the European regulatory limit for infants and children’s products (10 μg L⁻¹). The method is rapid, enviroment-friendly, and reliable.

Graphical abstract

Active probing of the mechanical properties of biological and synthetic vesicles

BACKGROUND

The interest in mechanics of synthetic and biological vesicles has been continuously growing during the last decades. Liposomes serve as model systems for investigating fundamental membrane processes and properties. More recently, extracellular vesicles (EVs) have been investigated mechanically as well. EVs are widely studied in fundamental and applied sciences, but their material properties remained elusive until recently. Elucidating the mechanical properties of vesicles is essential to unveil the mechanisms behind a variety of biological processes, e.g. budding, vesiculation and cellular uptake mechanisms.

SCOPE OF REVIEW

The importance of mechanobiology for studies of vesicles and membranes is discussed, as well as the different available techniques to probe their mechanical properties. In particular, the mechanics of vesicles and membranes as obtained by nanoindentation, micropipette aspiration, optical tweezers, electrodeformation and electroporation experiments is addressed.

MAJOR CONCLUSIONS

EVs and liposomes possess an astonishing rich, diverse behavior. To better understand their properties, and for optimization of their applications in nanotechnology, an improved understanding of their mechanical properties is needed. Depending on the size of the vesicles and the specific scientific question, different techniques can be chosen for their mechanical characterization.

GENERAL SIGNIFICANCE

Understanding the mechanical properties of vesicles is necessary to gain deeper insight in the fundamental biological mechanisms involved in vesicle generation and cellular uptake. This furthermore facilitates technological applications such as using vesicles as targeted drug delivery vehicles. Liposome studies provide insight into fundamental membrane processes and properties, whereas the role and functioning of EVs in biology and medicine are increasingly elucidated.

Ti3C2 MXene quantum dot-encapsulated liposomes for photothermal immunoassays using a portable near-infrared imaging camera on a smartphone

Methods based on the photothermal effect (a common phenomenon in nature) have been widely applied in different fields; however, their application in bioanalysis has lagged behind. Herein, we designed a near-infrared (NIR) photothermal immunoassay for the qualitative or quantitative detection of prostate-specific antigen (PSA) using titanium carbide (Ti₃C₂) MXene quantum dot (QD)-encapsulated liposomes with high photothermal efficiency. This system involves a sandwich-type immunoreaction and photothermal measurements. Ti₃C₂ MXene QDs were utilized as innovative photothermal signal beacons and were encapsulated in liposomes for the labeling of the secondary antibody. The assay was carried out by coupling a low-cost microplate with a homemade 3D printed device. Under NIR-laser irradiation, the Ti₃C₂ MXene QDs converted the light energy into heat, and a shift in temperature corresponding with the analyte concentration was obtained on a handheld thermometer. Under optimal conditions, the Ti₃C₂ MXene QD-based photothermal immunoassay exhibited a dynamic linear range from 1.0 ng mL^-1 to 50 ng mL^-1 with a limit of detection of 0.4 ng mL^-1 for PSA detection. Also, we constructed portable equipment using a portable near-infrared imaging camera to collect visual thermal data for the semi-quantitative analysis of the target PSA within 3 min. The specificity, reproducibility and accuracy of the photothermal immunoassay were acceptable. Importantly, our strategy opens new opportunities for protein point-of-care (POC) testing and biosecurity diagnostics.

Tethering functionality to lipid interfaces by a fast, simple and controllable post synthesis method

HYPOTHESIS

Liposomes require careful control of the surface design to ensure colloidal stability in complex matrices and target-specific binding to desired receptor units. Ideally, surface functionalization should be smart and controllable in terms of composition which is seldomly achieved by conventional methods. Therefore, a new strategy (insertion method) was developed and compared to the standard method (modification post-synthesis) using the model receptor biotin.

EXPERIMENTS

Dipalmitoylphosphatidylethanolamine-biotin (DPPE-biotin) was used in both procedures, lipopeptide-biotin and cholesterol-biotin were tested additionally for insertion into the intact lipid bilayer. The insertion method was optimized regarding incubation time, temperature and vesicle stability. The biotinylated vesicles of both functionalization methods were characterized with respect to their size, ζ-potential and binding functionality.

FINDINGS

Standard incorporation resulted in large variations in insertion-efficiency, high batch-to-batch differences, and an incorporation limit of 4 mol%. Best results were obtained through effortless insertion of the lipopeptide-biotin at room temperature. The concentration-controlled functionalization of liposomes (up to 10 mol%) could easily be monitored by the ζ-potential, resulted in reliable, quantitative binding to streptavidin and did not affect the analytical properties of the nanomaterial. This offers the possibility for a general modification strategy for lipid-based nanomaterials ideal for assay optimizations or multi-analyte detection.

Innovative Solutions for the Control of Leishmaniases: Nanoscale Drug Delivery Systems

Background:

Leishmania are sandfly-transmitted protozoan parasites that harbour within the macrophages of a mammalian host and cause leishmaniasis, a serious zoonotic disease that threatens the lives of millions worldwide. Its numerous forms (cutaneous, mucocutaneous, and visceral) are currently treated with a sparse arsenal of drugs, specifically antimonials, amphotericin B, miltefosine, and paromomycin, for which drug resistance and clinical failure are rampant. Medicine is presently trending towards nanotechnology to aid in the successful delivery of drugs. Vehicles such as lipid-based nanocarriers, polymer-based nanoparticles, and metal ions and oxides have been previously demonstrated to improve bioavailability of drugs and decrease toxicity for the patient. These cutting-edge solutions can be combined with existing active molecules, as well as novel drugs or plant extracts with promising antileishmanial activity.

Conclusion:

This review explores the current evidence for the treatment of leishmaniases using nanoscale drug delivery systems (specifically lipid-, polymer- and metal-based systems) and encourages further development of the aforementioned nanotechnologies for treatment of Leishmania.

Magnetoliposomes of mixed biomimetic and inorganic magnetic nanoparticles as enhanced hyperthermia agents

Recently, liposomes have been explored as a potential solution to improve the biocompatibility and the colloidal stability of magnetic nanoparticles. Protocols have been developed for producing magnetoliposomes of magnetite nanoparticles obtained inorganically (MNPs). However, the biomimetic synthesis of magnetite using heterologous proteins from magnetotactic bacteria has become a real alternative to produce novel biomimetic magnetic nanoparticles (BMNPs). Among these, the BMNPs obtained in presence of MamC protein from Magnetococcus marinus MC-1 have been proposed as excellent candidates to be potentially used as drug nanocarriers and as hyperthermia agents. However, their colloidal stability still needs to be improved while maintaining their magnetic properties intact. One possibility explored in this manuscript is to form magnetoliposomes that contain BMNPs. Indeed, the protocols developed for producing magnetoliposomes of MNPs need to be tested and modified to be able to include BMNPs. In this context, a protocol has been developed to produce both magnetoliposomes filled with MNPs and/or BMNPs and their potential as hyperthermia agents was tested. In fact, for the first time, these two types of nanoparticles were mixed in different proportions to test the composition that would optimize such as behaviour as hyperthermia agents. Interestingly, it was observed that the hyperthermia behaviour of the magnetoliposomes greatly improved if they were filled with a mixture of MNPs and BMNPs. These results indicate that these magnetoliposomes display optimal characteristics to become a potential agent for hyperthermia and that the opening of those liposomes could be externally controlled by applying an alternate magnetic field.

Study on intracellular delivery of liposome encapsulated quantum dots using advanced fluorescence microscopy

Quantum dots increasingly gain popularity for in vivo applications. However, their delivery and accumulation into cells can be challenging and there is still lack of detailed information. Thereby, the application of advanced fluorescence techniques can expand the portfolio of useful parameters for a more comprehensive evaluation. Here, we encapsulated hydrophilic quantum dots into liposomes for studying cellular uptake of these so-called lipodots into living cells. First, we investigated photophysical properties of free quantum dots and lipodots observing changes in the fluorescence decay time and translational diffusion behaviour. In comparison to empty liposomes, lipodots exhibited an altered zeta potential, whereas their hydrodynamic size did not change. Fluorescence lifetime imaging microscopy (FLIM) and fluorescence correlation spectroscopy (FCS), both combined with two-photon excitation (2P), were used to investigate the interaction behaviour of lipodots with an insect epithelial tissue. In contrast to the application of free quantum dots, their successful delivery into the cytosol of salivary gland duct cells could be observed when applying lipodots. Lipodots with different lipid compositions and surface charges did not result in considerable differences in the intracellular labelling pattern, luminescence decay time and diffusion behaviour. However, quantum dot degradation after intracellular accumulation could be assumed from reduced luminescence decay times and blue-shifted luminescence signals. In addition to single diffusing quantum dots, possible intracellular clustering of quantum dots could be assumed from increased diffusion times. Thus, by using a simple and manageable liposome carrier system, 2P-FLIM and 2P-FCS recording protocols could be tested, which are promising for investigating the fate of quantum dots during cellular interaction.

Resveratrol-Loaded Lipid Nanocarriers Are Internalized By Endocytosis in Yeast

Different positive pharmacological effects have been attributed to the natural product resveratrol (RSV), including antioxidant, antiaging, and cancer chemopreventive properties. However, its low bioavailability and rapid metabolic degradation has led to the suspicion that many of the biological activities of this compound observed in vitro may not be attainable in humans. To improve its bioavailability and pharmacokinetic profile, attempts have been made to encapsulate RSV into lipid-based nanocarrier systems. Here, the dioctadecyldimethylammonium bromide (DODAB):monoolein (MO) liposomal system (1:2) loaded with RSV revealed appropriate characteristics for drug release purposes: reduced size for cellular uptake (157 ± 23 nm), stability up to 80 days, positive surface charge (ζ ≈ +40 mV), and a controlled biphasic release of RSV from the lipid nanocarriers over a period of almost 50 h at pH 5.0 and 7.4. Moreover, the encapsulation efficiency of the nanocarrier ranged from 70% to 92% and its RSV loading capacity from 9% to 14%, when [RSV] was between 100 and 200 μM. The partition coefficient ( K_p) of RSV between lipid and aqueous phase was log K_p = 3.37 ± 0.10, suggesting moderate to high lipophilicity of this natural compound and reinforcing the lipid nanocarriers' suitability for RSV incorporation. The thermodynamic parameters of RSV partitioning in the lipid nanocarriers at 37 °C (Δ H = 43.76 ± 5.68 kJ mol^-1; Δ S = 0.20 ± 0.005 kJ mol^-1; and Δ G = -18.46 ± 3.48 kJ mol^-1) reflected the spontaneity of the process and the establishment of hydrophobic interactions. The cellular uptake mechanism of the RSV-loaded nanocarriers labeled with the lipophilic fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH) was studied in the eukaryotic model system Saccharomyces cerevisiae. Thirty minutes after incubation, yeast cells readily internalized nanocarriers and the spots of blue fluorescence of DPH clustered around the central vacuole in lipid droplets colocalized with the green fluorescence of the lipophilic endocytosis probe FM1-43. Subsequent studies with the endocytosis defective yeast deletion mutant ( end3Δ) and with the endocytosis inhibitor methyl-β-cyclodextrin supported the involvement of an endocytic pathway. This novel nanotechnology approach opens good perspectives for medical applications.

Synthetic Minimal Cell: Self-Reproduction of the Boundary Layer

A critical aspect in the bottom-up construction of a synthetic minimal cell is to develop an entity that is capable of self-reproduction. A key role in this process is the expansion and division of the boundary layer that surrounds the compartment, a process in which content loss has to be avoided and the barrier function maintained. Here, we describe the latest developments regarding self-reproduction of a boundary layer with a focus on the growth and division of phospholipid-based membranes in the context of a synthetic minimal cell.

AFM Study on Superlubricity between Ti6Al4V/Polymer Surfaces Achieved with Liposomes

Liposomes have been considered as the boundary lubricant in natural joints. They are also the main component of bionic lubricant. In this study, the tribological properties of liposomes on Ti6Al4V/polymer surface were studied by atomic force microscope (AFM) at the nanoscale. The superlubricity with a friction coefficient of 0.007 was achieved under the maximal pressure of 15 MPa, consisting with the lubrication condition of natural joints. Especially, when the AFM probe was hydrophilically modified and preadsorbed, the friction coefficient and load bearing capacity could be further improved. In addition, the probe with a large radius could maintain the stable lubrication of liposomes in the contact zone. Finally, an optimal lubrication model of liposomes was established and the critical force for superlubricity was also proposed. It was the boundary between elastic deformation and plastic deformation for vesicles. It was also the indicator of the plough effect appearing on the adsorbed layer. This work reveals the interfacial behavior of liposomes and realizes the controllable superlubricity system, providing more guidance for clinical application.

Application of liposome membrane as the reaction field: A case study using the Horner-Wadsworth-Emmons reaction

The properties of the liposome membrane as a reaction field were investigated by focusing on the Horner-Wadsworth-Emmons reaction as a case study. Use of the liposomes existing in the gel phase resulted in the enhanced activity of the substrates and furnished the products with same E/Z stereoselectivity as in the liposome-free system. The membrane environment in the gel phase most likely assisted the formation of adducts that induced selective generation of the E-isomer. The possible role of liposomes is to assist the proton removal from the reactant, rather than providing the basic interfacial environment.

Cubosomes: The Next Generation of Smart Lipid Nanoparticles?

Cubosomes are highly stable nanoparticles formed from the lipid cubic phase and stabilized by a polymer based outer corona. Bicontinuous lipid cubic phases consist of a single lipid bilayer that forms a continuous periodic membrane lattice structure with pores formed by two interwoven water channels. Cubosome composition can be tuned to engineer pore sizes or include bioactive lipids, the polymer outer corona can be used for targeting and they are highly stable under physiological conditions. Compared to liposomes, the structure provides a significantly higher membrane surface area for loading of membrane proteins and small drug molecules. Owing to recent advances, they can be engineered in vitro in both bulk and nanoparticle formats with applications including drug delivery, membrane bioreactors, artificial cells, and biosensors. This review outlines recent advances in cubosome technology enabling their application and provides guidelines for the rational design of new systems for biomedical applications.

A 3D printing-based portable photoelectrochemical sensing device using a digital multimeter

An enzyme-free photoelectrochemical sensing method based on a 3D-printing device was developed for CEA detection coupling glucose-encapsulated liposomes with digital multimeter readout.

Nanoscale Chemical Imaging of Individual, Chemotherapeutic Cytarabine-loaded Liposomal Nanocarriers

Dosage of chemotherapeutic drugs is a tradeoff between efficacy and side-effects. Liposomes are nanocarriers that increase therapy efficacy and minimize side-effects by delivering otherwise difficult to administer therapeutics with improved efficiency and selectivity. Still, variabilities in liposome preparation require assessing drug encapsulation efficiency at the single liposome level, an information that, for non-fluorescent therapeutic cargos, is inaccessible due to the minute drug load per liposome. Photothermal induced resonance (PTIR) provides nanoscale compositional specificity, up to now, by leveraging an atomic force microscope (AFM) tip contacting the sample to transduce the sample's photothermal expansion. However, on soft samples (e.g. liposomes) PTIR effectiveness is reduced due to the likelihood of tip-induced sample damage and inefficient AFM transduction. Here, individual liposomes loaded with the chemotherapeutic drug cytarabine are deposited intact from suspension via nES-GEMMA (nano-electrospray gas-phase electrophoretic mobility molecular analysis) collection and characterized at the nanoscale with the chemically-sensitive PTIR method. A new tapping-mode PTIR imaging paradigm based on heterodyne detection is shown to be better adapted to measure soft samples, yielding cytarabine distribution in individual liposomes and enabling classification of empty and drug-loaded liposomes. The measurements highlight PTIR capability to detect ≈ 103 cytarabine molecules (≈ 1.7 zmol) label-free and non-destructively.

Light-Driven Biocatalysis in Liposomes and Polymersomes: Where Are We Now?

The utilization of light energy to power organic-chemical transformations is a fundamental strategy of the terrestrial energy cycle. Inspired by the elegance of natural photosynthesis, much interdisciplinary research effort has been devoted to the construction of simplified cell mimics based on artificial vesicles to provide a novel tool for biocatalytic cascade reactions with energy-demanding steps. By inserting natural or even artificial photosynthetic systems into liposomes or polymersomes, the light-driven proton translocation and the resulting formation of electrochemical gradients have become possible. This is the basis for the conversion of photonic into chemical energy in form of energy-rich molecules such as adenosine triphosphate (ATP), which can be further utilized by energy-dependent biocatalytic reactions, e.g. carbon fixation. This review compares liposomes and polymersomes as artificial compartments and summarizes the types of light-driven proton pumps that have been employed in artificial photosynthesis so far. We give an overview over the methods affecting the orientation of the photosystems within the membranes to ensure a unidirectional transport of molecules and highlight recent examples of light-driven biocatalysis in artificial vesicles. Finally, we summarize the current achievements and discuss the next steps needed for the transition of this technology from the proof-of-concept status to preparative applications.

DNA Oligonucleotide-Functionalized Liposomes: Bioconjugate Chemistry, Biointerfaces, and Applications

Interfacing DNA with liposomes has produced a diverse range of programmable soft materials, devices, and drug delivery vehicles. By simply controlling liposomal composition, bilayer fluidity, lipid domain formation, and surface charge can be systematically varied. Recent development in DNA research has produced not only sophisticated nanostructures but also new functions including ligand binding and catalysis. For noncationic liposomes, a DNA is typically covalently linked to a hydrophobic or lipid moiety that can be inserted into lipid membranes. In this article, we discuss fundamental biointerfaces formed between DNA and noncationic liposomes. The methods to prepare such conjugates and the interactions at the membrane interfaces are also discussed. The effect of DNA lateral diffusion on fluid bilayer membranes and the effect of membrane on DNA assembly are emphasized. DNA hybridization can be programmed to promote fusion of lipid membranes. Representative applications of this conjugate for drug delivery, biosensor development, and directed assembly of materials are briefly described toward the end. Some future research directions are also proposed to further understand this biointerface.

Nanoparticles for postinfarct ventricular remodeling

In recent years, tremendous progress has been made in the treatment of acute myocardial infarction, but pathological ventricular remodeling often causes survivors to suffer from fatal heart failure. Currently, there is no effective therapy to attenuate ventricular remodeling. Recently, nanoparticle-based drug delivery systems are widely applied in biomedicine especially in cancer and liver fibrosis, owing to its excellent physical, chemical and biological properties. Therefore, the use of nanoparticles as delivery vehicles of small molecules, polypeptides, etc. to improve postinfarct ventricular remodeling is expected. In this review, we summarize the updated researches in this fast-growing area and suggest further works needed.

Enhanced Fluorescent Protein Activity in Polymer Scaffold-Stabilized Phospholipid Nanoshells Using Neutral Redox Initiator Polymerization Conditions

Phospholipid nanoshells, for example, liposomes, provide a versatile enabling platform for the development of nanometer-sized biosensors and molecular delivery systems. Utilization of phospholipid nanoshells is limited by the inherent instability in complex biological environments, where the phospholipid nanoshell may disassemble and degrade, thus releasing the contents and destroying sensor function. Polymer scaffold stabilization (PSS), wherein the phospholipid nanoshells are prepared by partitioning reactive monomers into the lipid bilayer lamella followed by radical polymerization, has emerged to increase phospholipid nanoshell stability. In this work, we investigated the effects of three different radical initiator conditions to fabricate stable PSS-phospholipid nanoshells yet retain the activity of encapsulated model fluorescent sensor proteins. To identify nondestructive initiation conditions, UV photoinitiation, neutral redox initiation, and thermal initiation were investigated as a function of PSS-phospholipid nanoshell stabilization and fluorescence emission intensity of enhanced green fluorescent protein (eGFP) and tandem dimer Tomato (td-Tomato). All three initiator approaches yielded comparably stable PSS-phospholipid nanoshells, although slight variations in PSS-phospholipid nanoshell size were observed, ranging from ca. 140 nm for unstabilized phospholipid nanoshells to 300-500 nm for PSS-phospholipid nanoshells. Fluorescence emission intensity of encapsulated eGFP was completely attenuated under thermal initiation (0% vs control), moderately attenuated under UV photoinitiation (40 ± 4% vs control), and unaffected by neutral redox initiation (97 ± 3% vs control). Fluorescence emission intensity of encapsulated td-Tomato was significantly attenuated under thermal initiation (13 ± 3% vs control), moderately attenuated UV photoinitiation (64 ± 5% vs control), and unaffected by neutral redox initiation (98% ± 4% vs control). Therefore, the neutral redox initiation method provides a significant advancement toward the preparation of protein-functionalized PSS-phospholipid nanoshells. These results should help to guide future applications and designs of biosensor platforms using PSS-phospholipid nanoshells and other polymer systems employing protein transducers.

Post-translational and transcriptional dynamics - regulating extracellular vesicle biology

Introduction: Extracellular vesicles (EVs) are secreted into their extracellular environment, contain a specific repertoire of cellular cargo, and represent a novel vehicle for cell-cell communication. Protein post-translational modifications (PTMs) are emerging as major effectors of EV biology and function, and in turn, regulate cellular signaling. Areas covered: Discovery and investigation of PTMs such as methylation, glycosylation, acetylation, phosphorylation, sumoylation, and many others has established fundamental roles for PTMs within EVs and associated EV function. The application of enrichment strategies for modifications, high-resolution quantitative mass spectrometry-based proteomics, and improved technological approaches have provided key insights into identification and characterization of EV-based PTMs. Recently, an overwhelming appreciation for the diversity of modifications, including post-transcriptional modifications, dynamic roles of these modifications, and their emerging interplay, including protein-protein, protein-lipid, protein-RNA, and variable RNA modifications, is emerging. At a cellular level, such interplay is essential for gene expression/genome organization, protein function and localization, RNA metabolism, cell division, and cell signaling. Expert commentary: The understanding of these modifications and interactions will provide strategies toward how distinct cargo is localized, sorted, and delivered through EVs to mediate intercellular function, with further understanding of such modifications and intermolecular interactions will provide advances in EV-based therapeutic strategies.

Liposome: composition, characterisation, preparation, and recent innovation in clinical applications

In the last decades, pharmaceutical interested researches aimed to develop novel and innovative drug delivery techniques in the medical and pharmaceutical fields. Recently, phospholipid vesicles (Liposomes) are the most known versatile assemblies in the drug delivery systems. The discovery of liposomes arises from self-forming enclosed phospholipid bilayer upon coming in contact with the aqueous solution. Liposomes are uni or multilamellar vesicles consisting of phospholipids produced naturally or synthetically, which are readily non-toxic, biodegradable, and are readily produced on a large scale. Various phospholipids, for instance, soybean, egg yolk, synthetic, and hydrogenated phosphatidylcholine consider the most popular types used in different kinds of formulations. This review summarises liposomes composition, characterisation, methods of preparation, and their applications in different medical fields including cancer therapy, vaccine, ocular delivery, wound healing, and some dermatological applications.

Light scattering corrections to linear dichroism spectroscopy for liposomes in shear flow using calcein fluorescence and modified Rayleigh-Gans-Debye-Mie scattering

The interpretation of data from absorbance spectroscopy experiments of liposomes in flow systems is often complicated by the fact that there is currently no easy way to account for scattering artefacts. This has proved particularly problematic for linear dichroism (LD) spectroscopy, which may be used to determine binding modes of small molecules, peptides and proteins to liposomes if we can extract the absorbance signal from the combined absorbance/scattering experiment. Equations for a modified Rayleigh-Gans-Debye (RGD) approximation to the turbidity (scattering) LD spectrum are available in the literature though have not been implemented. This review summarises the literature and shows how it can be implemented. The implementation proceeds by first determining volume loss that occurs when a spherical liposome is subjected to flow. Calcein fluorescence can be used for this purpose since at high concentrations (> 60 mM) it has low intensity fluorescence with maxima at 525 and 563 nm whereas at low concentrations (<1 mM) the fluorescence intensity is enhanced and the band shifts to 536 nm. The scattering calculation process yields the average axis ratios of the distorted liposome ellipsoids and extent of orientation of the liposomes in flow. The scattering calculations require methods to estimate liposome integrity, volume loss, and orientation when subjected to shear stresses under flow.

Large-Scale Preparation of Giant Vesicles by Squeezing a Lipid-Coated Marshmallow-like Silicone Gel in a Buffer

Giant vesicles were efficiently produced by squeezing a lipid (l-α-phosphatidylcholine from egg yolk)-coated marshmallow-like flexible macroporous silicone monolith in a buffer. The mean diameter of the obtained vesicles was 2 μm, showing a wide distribution, up to tens of micrometers, which was similar to that of vesicles formed by a natural swelling method. It was possible to prepare vesicle dispersions on a scale from several microliters to several hundred milliliters. A protein synthesis system (PURE system) contained in vesicles prepared using this method functioned effectively. Our absorbing-squeezing method is expected to help in studies that use giant vesicles such as artificial cells and drug delivery systems.

Single-Vesicle Assays Using Liposomes and Cell-Derived Vesicles: From Modeling Complex Membrane Processes to Synthetic Biology and Biomedical Applications

The plasma membrane is of central importance for defining the closed volume of cells in contradistinction to the extracellular environment. The plasma membrane not only serves as a boundary, but it also mediates the exchange of physical and chemical information between the cell and its environment in order to maintain intra- and intercellular functions. Artificial lipid- and cell-derived membrane vesicles have been used as closed-volume containers, representing the simplest cell model systems to study transmembrane processes and intracellular biochemistry. Classical examples are studies of membrane translocation processes in plasma membrane vesicles and proteoliposomes mediated by transport proteins and ion channels. Liposomes and native membrane vesicles are widely used as model membranes for investigating the binding and bilayer insertion of proteins, the structure and function of membrane proteins, the intramembrane composition and distribution of lipids and proteins, and the intermembrane interactions during exo- and endocytosis. In addition, natural cell-released microvesicles have gained importance for early detection of diseases and for their use as nanoreactors and minimal protocells. Yet, in most studies, ensembles of vesicles have been employed. More recently, new micro- and nanotechnological tools as well as novel developments in both optical and electron microscopy have allowed the isolation and investigation of individual (sub)micrometer-sized vesicles. Such single-vesicle experiments have revealed large heterogeneities in the structure and function of membrane components of single vesicles, which were hidden in ensemble studies. These results have opened enormous possibilities for bioanalysis and biotechnological applications involving unprecedented miniaturization at the nanometer and attoliter range. This review will cover important developments toward single-vesicle analysis and the central discoveries made in this exciting field of research.

Linear dichroism as a probe of molecular structure and interactions

Linear dichroism (LD) spectroscopy involves measuring the wavelength (or energy) dependence of the difference in absorption of light parallel and perpendicular to an orientation direction. It requires samples to have a net orientation. The aim of this review is to summarise some UV-visible linear dichroism (LD) methods that can be usefully applied to increase our understanding of biomacromolecules and their complexes that have a high aspect ratio. LD shares the advantages of most spectroscopic techniques including the fact that data collection is fairly straightforward and many sample types can be investigated. Conversely, LD shares the disadvantage that the measured signal is an average over all species in the sample on which the light beam is incident. LD mitigates this disadvantage somewhat in that only species which are oriented give a net signal. How the data can be analysed to give structural information about small molecules in stretched films and membrane systems or bound to biomacromolecules and directly about biomacromolecules such as DNA and protein fibres forms part of this review. In the UV-visible region LD often suffers noticeably from light scattering since the samples tend to be large relative to the wavelength of the incident light, so consideration is also given to data analysis challenges including removal of scattering contributions to an observed signal. Brief mention is made of fluorescence detected LD.

Reverse Transcription Polymerase Chain Reaction in Giant Unilamellar Vesicles

We assessed the applicability of giant unilamellar vesicles (GUVs) for RNA detection using in vesicle reverse transcription polymerase chain reaction (RT-PCR). We prepared GUVs that encapsulated one-pot RT-PCR reaction mixture including template RNA, primers, and Taqman probe, using water-in-oil emulsion transfer method. After thermal cycling, we analysed the GUVs that exhibited intense fluorescence signals, which represented the cDNA amplification. The detailed analysis of flow cytometry data demonstrated that rRNA and mRNA in the total RNA can be amplified from 10–100 copies in the GUVs with 5–10 μm diameter, although the fraction of reactable GUV was approximately 60% at most. Moreover, we report that the target RNA, which was directly transferred into the GUV reactors via membrane fusion, can be amplified and detected using in vesicle RT-PCR. These results suggest that the GUVs can be used as biomimetic reactors capable of performing PCR and RT-PCR, which are important in analytical and diagnostic applications with additional functions.

Exploring Molecular-Biomembrane Interactions with Surface Plasmon Resonance and Dual Polarization Interferometry Technology: Expanding the Spotlight onto Biomembrane Structure

The molecular analysis of biomolecular-membrane interactions is central to understanding most cellular systems but has emerged as a complex technical challenge given the complexities of membrane structure and composition across all living cells. We present a review of the application of surface plasmon resonance and dual polarization interferometry-based biosensors to the study of biomembrane-based systems using both planar mono- or bilayers or liposomes. We first describe the optical principals and instrumentation of surface plasmon resonance, including both linear and extraordinary transmission modes and dual polarization interferometry. We then describe the wide range of model membrane systems that have been developed for deposition on the chips surfaces that include planar, polymer cushioned, tethered bilayers, and liposomes. This is followed by a description of the different chemical immobilization or physisorption techniques. The application of this broad range of engineered membrane surfaces to biomolecular-membrane interactions is then overviewed and how the information obtained using these techniques enhance our molecular understanding of membrane-mediated peptide and protein function. We first discuss experiments where SPR alone has been used to characterize membrane binding and describe how these studies yielded novel insight into the molecular events associated with membrane interactions and how they provided a significant impetus to more recent studies that focus on coincident membrane structure changes during binding of peptides and proteins. We then discuss the emerging limitations of not monitoring the effects on membrane structure and how SPR data can be combined with DPI to provide significant new information on how a membrane responds to the binding of peptides and proteins.

Investigation on the Nanomechanics of Liposome Adsorption on Titanium Alloys: Temperature and Loading Effects

The mechanical properties of liposomes, determined by the lipid phase state at ambient temperature, have a close relationship with their physiological activities. Here, atomic force microscopy (AFM) was used to produce images and perform force measurements on titanium alloys at two adsorbed temperatures. The mechanical properties were evaluated under repeated loading and unloading, suggesting a better reversibility and resistance of gel phase liposomes. The liquid phase liposomes were irreversibly damaged during the first approach while the gel phase liposomes could bear more iterations, resulting from water flow reversibly going across the membranes. The statistical data offered strong evidence that the lipid membranes in the gel phase are robust enough to resist the tip penetration, mainly due to their orderly organization and strong hydrophobic interactions between lipid molecules. This work regarding the mechanical properties of liposomes with different phases provides guidance for future clinical applications, such as artificial joints.

Integrity of Membrane Structures in Giant Unilamellar Vesicles as Assay for Antioxidants and Prooxidants

We have attempted to evaluate, on the basis of optical microscopy for a single giant unilamellar vesicle (GUV), the potency of antioxidants in protecting GUV membranes from oxidative destruction. Photosensitized membrane budding of GUVs prepared from soybean phosphatidylcholine with chlorophyll a (Chl a) and β-carotene (β-Car) as photosensitizer and protector, respectively, were followed by microscopic imaging. A dimensionless entropy parameter, ΔE, as derived from the time-resolved microscopic images, was employed to describe the evolution of morphological variation of GUVs. As an indication of membrane instability, the budding process showed three successive temporal regimes as a common feature: a lag phase prior to the initiation of budding characterized by LP (in s), a budding phase when ΔE increased with a rate of kΔE (in s-1), and an ending phase with morphology stabilized at a constant ΔEend (dimensionless). We show that the phase-associated parameters can be objectively obtained by fitting the ΔE-t kinetics curves to a Boltzmann function and that all of the parameters are rather sensitive to β-Car concentration. As for the efficacy of these parameters in quantifying the protection potency of β-Car, kΔE is shown to be most sensitive for β-Car in a concentration regime of biological significance of <1 × 10-7 M, whereas LP and ΔEend are more sensitive for β-Car concentrations exceeding 1 × 10-7 M. Furthermore, based on the results of GUV imaging and fluorescence and Raman spectroscopies, we have revealed for different phases the mechanistic interplay among 1O2* diffusion, PC-OOH accumulation, Chl a and/or β-Car consumption, and the morphological variation. The developed assay should be valuable for characterizing the potency of antioxidants or prooxidants in the protection or destruction of the membrane integrity of GUVs.