Biologically Complex Planar Cell Plasma Membranes Supported on Polyelectrolyte Cushions Enhance Transmembrane Protein Mobility and Retain Native Orientation

Rapid Enrichment of a Native Multipass Transmembrane Protein via Cell Membrane Electrophoresis through Buffer pH and Ionic Strength Adjustment

Supported membrane electrophoresis is a promising technique for collecting membrane proteins in native bilayer environments. However, the slow mobility of typical transmembrane proteins has impeded the technique's advancement. Here, we successfully applied cell membrane electrophoresis to rapidly enrich a 12-transmembrane helix protein, glucose transporter 1 with antibodies (GLUT1 complex), by tuning the buffer pH and ionic strength. The identified conditions allowed the separation of the GLUT1 complex and a lipid probe, Fast-DiO, within a native-like environment in a few minutes. A force model was developed to account for distinct electric and drag forces acting on the transmembrane and aqueous-exposed portion of a transmembrane protein as well as the electroosmotic force. This model not only elucidates the impact of size and charge properties of transmembrane proteins but also highlights the influence of pH and ionic strength on the driving forces and, consequently, electrophoretic mobility. Model predictions align well with experimentally measured electrophoretic mobilities of the GLUT1 complex and Fast-DiO at various pH and ionic strengths as well as with several lipid probes, lipid-anchored proteins, and reconstituted membrane proteins from previous studies. Force analyses revealed the substantial membrane drag of the GLUT1 complex, significantly slowing down electrophoretic mobility. Besides, the counterbalance of similar magnitudes of electroosmotic and electric forces results in a small net driving force and, consequently, reduced mobility under typical neutral pH conditions. Our results further highlight how the size and charge properties of transmembrane proteins influence the suitable range of operating conditions for effective movement, providing potential applications for concentrating and isolating membrane proteins within this platform.

Plant Membrane-On-A-Chip: A Platform for Studying Plant Membrane Proteins and Lipids

The cell plasma membrane is a two-dimensional, fluid mosaic material composed of lipids and proteins that create a semipermeable barrier defining the cell from its environment. Compared with soluble proteins, the methodologies for the structural and functional characterization of membrane proteins are challenging. An emerging tool for studies of membrane proteins in mammalian systems is a "plasma membrane on a chip," also known as a supported lipid bilayer. Here, we create the "plant-membrane-on-a-chip,″ a supported bilayer made from the plant plasma membranes of Arabidopsis thaliana, Nicotiana benthamiana, or Zea mays. Membrane vesicles from protoplasts containing transgenic membrane proteins and their native lipids were incorporated into supported membranes in a defined orientation. Membrane vesicles fuse and orient systematically, where the cytoplasmic side of the membrane proteins faces the chip surface and constituents maintain mobility within the membrane plane. We use plant-membrane-on-a-chip to perform fluorescent imaging to examine protein-protein interactions and determine the protein subunit stoichiometry of FLOTILLINs. We report here that like the mammalian FLOTILLINs, FLOTILLINs expressed in Arabidopsis form a tetrameric complex in the plasma membrane. This plant-membrane-on-a-chip approach opens avenues to studies of membrane properties of plants, transport phenomena, biophysical processes, and protein-protein and protein-lipid interactions in a convenient, cell-free platform.

Solid-State Molecular Protonics Devices of Solid-Supported Biological Membranes Reveal the Mechanism of Long-Range Lateral Proton Transport

Lateral proton transport (PT) on the surface of biological membranes is a fundamental biochemical process in the bioenergetics of living cells, but a lack of available experimental techniques has resulted in a limited understanding of its mechanism. Here, we present a molecular protonics experimental approach to investigate lateral PT across membranes by measuring long-range (70 μm) lateral proton conduction via a few layers of lipid bilayers in a solid-state-like environment, i.e., without having bulk water surrounding the membrane. This configuration enables us to focus on lateral proton conduction across the surface of the membrane while decoupling it from bulk water. Hence, by controlling the relative humidity of the environment, we can directly explore the role of water in the lateral PT process. We show that proton conduction is dependent on the number of water molecules and their structure and on membrane composition, where we explore the role of the headgroup, the tail saturation, the membrane phase, and membrane fluidity. The measured PT as a function of temperature shows an inverse temperature dependency, which we explain by the desorption and adsorption of water molecules into the solid membrane platform. We explain our findings by discussing the role of percolating hydrogen bonding within the membrane structure in a Grotthuss-like mechanism.

Synthesis and Characterization of Stimuli-Responsive Polymer Brushes in Nanofluidic Channels

Nanochannels with controllable gating behavior are attractive features in a wide range of nanofluidic applications including viral detection, particle sorting, and flow regulation. Here, we use selective sidewall functionalization of nanochannels with a polyelectrolyte brush to investigate the channel gating response to variations in solution pH and ionic strength. The conformational and structural changes of the interfacial brush layer within the channels are interrogated by specular and off-specular neutron reflectometry. Simultaneous fits of the specular and off-specular signals, using a dynamical theory model and a fitting optimization protocol, enable detailed characterization of the brush conformations and corresponding channel geometry under different solution conditions. Our results indicate a collapsed brush state under basic pH, equivalent to an open gate, and an expanded brush state representing a partially closed gate upon decreasing the pH and salt concentration. These findings open new possibilities in noninvasive in situ characterization of tunable nanofluidics and lab-on-chip devices with advanced designs and improved functionality.

Using the Water Absorption Ability of Dried Hydrogels to Form Hydrogel-Supported Lipid Bilayers

The formation of supported lipid bilayers (SLBs) on hydrogels can act as a biocompatible anti-fouling interface. However, generating continuous and mobile SLBs on materials other than conventional glass or mica remains a significant challenge. The interaction between lipid membrane vesicles and a typical hydrogel is usually insufficient to induce membrane vesicle rupture and form a planar lipid membrane. In this study, we demonstrate that the water absorption ability of a dried polyacrylamide (PAAm) hydrogel could serve as a driving force to facilitate the formation of the hydrogel-SLBs. The absorption driving force vanishes after the hydrogels are fully hydrated, leaving no extra interaction hindering lipid lateral mobility in the formed SLBs. Our fluorescence recovery after photobleaching (FRAP) results show that SLBs only form on hydrogels with adequate absorption abilities. Moreover, we discovered that exposure to oxygen during drying could lead to the formation of an oxidized crust on the PAAm hydrogel surface, impeding SLB formation. Therefore, minimizing oxygen exposure during drying is crucial to achieving high-quality hydrogel surfaces for SLB formation. This water absorption method enables the straightforward fabrication of hydrogel-SLBs without the need for additional substrates or charges, thereby expanding their potential applications.

Bacterial Membrane Mimetics: From Biosensing to Disease Prevention and Treatment

Plasma membrane mimetics can potentially play a vital role in drug discovery and immunotherapy owing to the versatility to assemble facilely cellular membranes on surfaces and/or nanoparticles, allowing for direct assessment of drug/membrane interactions. Recently, bacterial membranes (BMs) have found widespread applications in biomedical research as antibiotic resistance is on the rise, and bacteria-associated infections have become one of the major causes of death worldwide. Over the last decade, BM research has greatly benefited from parallel advancements in nanotechnology and bioelectronics, resulting in multifaceted systems for a variety of sensing and drug discovery applications. As such, BMs coated on electroactive surfaces are a particularly promising label-free platform to investigate interfacial phenomena, as well as interactions with drugs at the first point of contact: the bacterial membrane. Another common approach suggests the use of lipid-coated nanoparticles as a drug carrier system for therapies for infectious diseases and cancer. Herein, we discuss emerging platforms that make use of BMs for biosensing, bioimaging, drug delivery/discovery, and immunotherapy, focusing on bacterial infections and cancer. Further, we detail the synthesis and characteristics of BMs, followed by various models for utilizing them in biomedical applications. The key research areas required to augment the characteristics of bacterial membranes to facilitate wider applicability are also touched upon. Overall, this review provides an interdisciplinary approach to exploit the potential of BMs and current emerging technologies to generate novel solutions to unmet clinical needs.

Interaction Kinetics of Individual mRNA-Containing Lipid Nanoparticles with an Endosomal Membrane Mimic: Dependence on pH, Protein Corona Formation, and Lipoprotein Depletion

Lipid nanoparticles (LNPs) have emerged as potent carriers for mRNA delivery, but several challenges remain before this approach can offer broad clinical translation of mRNA therapeutics. To improve their efficacy, a better understanding is required regarding how LNPs are trapped and processed at the anionic endosomal membrane prior to mRNA release. We used surface-sensitive fluorescence microscopy with single LNP resolution to investigate the pH dependency of the binding kinetics of ionizable lipid-containing LNPs to a supported endosomal model membrane. A sharp increase of LNP binding was observed when the pH was lowered from 6 to 5, accompanied by stepwise large-scale LNP disintegration. For LNPs preincubated in serum, protein corona formation shifted the onset of LNP binding and subsequent disintegration to lower pH, an effect that was less pronounced for lipoprotein-depleted serum. The LNP binding to the endosomal membrane mimic was observed to eventually become severely limited by suppression of the driving force for the formation of multivalent bonds during LNP attachment or, more specifically, by charge neutralization of anionic lipids in the model membrane due to their association with cationic lipids from earlier attached LNPs upon their disintegration. Cell uptake experiments demonstrated marginal differences in LNP uptake in untreated and lipoprotein-depleted serum, whereas lipoprotein-depleted serum increased mRNA-controlled protein (eGFP) production substantially. This complies with model membrane data and suggests that protein corona formation on the surface of the LNPs influences the nature of the interaction between LNPs and endosomal membranes.

Impedance sensing of antibiotic interactions with a pathogenic E. coli outer membrane supported bilayer

Antibiotic resistance is a growing global health concern due to the decreasing number of antibiotics available for therapeutic use as more drug-resistant bacteria develop. Changes in the membrane properties of Gram-negative bacteria can influence their response to antibiotics and give rise to resistance. Thus, understanding the interactions between the bacterial membrane and antibiotics is important for elucidating microbial membrane properties to use for designing novel antimicrobial drugs. To study bacterial membrane-antibiotic interactions, we created a surface-supported planar bacterial outer membrane model on an optically-transparent, conducting polymer surface (poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)). This model enables membrane characterization using fluorescence microscopy and electrochemical impedance spectroscopy (EIS). The membrane platform is fabricated using outer membrane vesicles (OMVs) isolated from clinically relevant Gram-negative bacteria, enterohemorrhagic Escherichia coli. This approach enables us to mimic the native components of the bacterial membrane by incorporating native lipids, membrane proteins, and lipopolysaccharides. Using EIS, we determined membrane impedance and captured membrane-antibiotic interactions using the antibiotics polymyxin B, bacitracin, and meropenem. This sensor platform incorporates aspects of the biological complexity found in bacterial outer membranes and, by doing so, offers a powerful, biomimetic approach to the study of antimicrobial drug interactions.

Advances in Cell-Conductive Polymer Biointerfaces and Role of the Plasma Membrane

The plasma membrane (PM) is often described as a wall, a physical barrier separating the cell cytoplasm from the extracellular matrix (ECM). Yet, this wall is a highly dynamic structure that can stretch, bend, and bud, allowing cells to respond and adapt to their surrounding environment. Inspired by shapes and geometries found in the biological world and exploiting the intrinsic properties of conductive polymers (CPs), several biomimetic strategies based on substrate dimensionality have been tailored in order to optimize the cell-chip coupling. Furthermore, device biofunctionalization through the use of ECM proteins or lipid bilayers have proven successful approaches to further maximize interfacial interactions. As the bio-electronic field aims at narrowing the gap between the electronic and the biological world, the possibility of effectively disguising conductive materials to "trick" cells to recognize artificial devices as part of their biological environment is a promising approach on the road to the seamless platform integration with cells.

Dual Mode Sensing of Binding and Blocking of Cancer Exosomes to Biomimetic Human Primary Stem Cell Surfaces

Cancer-derived exosomes (cEXOs) facilitate transfer of information between tumor and human primary stromal cells, favoring cancer progression. Although the mechanisms used during this information exchange are still not completely understood, it is known that binding is the initial contact established between cEXOs and cells. Hence, studying binding and finding strategies to block it are of great therapeutic value. However, such studies are challenging for a variety of reasons, including the need for human primary cell culture, the difficulty in decoupling and isolating binding from internalization and cargo delivery, and the lack of techniques to detect these specific interactions. In this work, we created a supported biomimetic stem cell membrane incorporating membrane components from human primary adipose-derived stem cells (ADSCs). We formed the supported membrane on glass and on multielectrode arrays to offer the dual option of optical or electrical detection of cEXO binding to the membrane surface. Using our platform, we show that cEXOs bind to the stem cell membrane and that binding is blocked when an antibody to integrin β1, a component of ADSC surface, is exposed to the membrane surface prior to cEXOs. To test the biological outcome of blocking this interaction, we first confirm that adding cEXOs to cultured ADSCs leads to the upregulation of vascular endothelial growth factor, a measure of proangiogenic activity. Next, when ADSCs are first blocked with anti-integrin β1 and then exposed to cEXOs, the upregulation of proangiogenic activity and cell proliferation are significantly reduced. This biomimetic membrane platform is the first cell-free label-free in vitro platform for the recapitulation and study of cEXO binding to human primary stem cells with potential for therapeutic molecule screening as it is compatible with scale-up and multiplexing.

Functional Infectious Nanoparticle Detector: Finding Viruses by Detecting Their Host Entry Functions Using Organic Bioelectronic Devices

Emerging viruses will continue to be a threat to human health and wellbeing into the foreseeable future. The COVID-19 pandemic revealed the necessity for rapid viral sensing and inhibitor screening in mitigating viral spread and impact. Here, we present a platform that uses a label-free electronic readout as well as a dual capability of optical (fluorescence) readout to sense the ability of a virus to bind and fuse with a host cell membrane, thereby sensing viral entry. This approach introduces a hitherto unseen level of specificity by distinguishing fusion-competent viruses from fusion-incompetent viruses. The ability to discern between competent and incompetent viruses means that this device could also be used for applications beyond detection, such as screening antiviral compounds for their ability to block virus entry mechanisms. Using optical means, we first demonstrate the ability to recapitulate the entry processes of influenza virus using a biomembrane containing the viral receptor that has been functionalized on a transparent organic bioelectronic device. Next, we detect virus membrane fusion, using the same, label-free devices. Using both reconstituted and native cell membranes as materials to functionalize organic bioelectronic devices, configured as electrodes and transistors, we measure changes in membrane properties when virus fusion is triggered by a pH drop, inducing hemagglutinin to undergo a conformational change that leads to membrane fusion.

Functional Reconstitution of Dopamine D2 Receptor into a Supported Model Membrane in a Nanometric Confinement

Dopamine D2 receptor (D2R), a G-protein-coupled receptor (GPCR), plays critical roles in neural functions and represents the target for a wide variety of drugs used to treat neurological diseases. However, its fundamental physicochemical properties, such as dimerization and affinity to different lipid environments, remain unknown. Here, reconstitution and characterization of D2R in a supported model membrane in nanometric confinement are reported. D2R is expressed in Chinese hamster ovary (CHO) cells and transferred into the supported model membrane as cell membrane blebs. D2R molecules are reconstituted with an elevated density in the cleft between the substrate and poly(dimethylsiloxane) (PDMS) elastomer. Reconstituted D2R retains the physiological functions, as evaluated from its binding to an antagonist and dimerization lifetime. The transient dimer formation of D2R, similar to the live cell, suggests that it is an innate property that does not depend on the cellular structures such as actin filaments. Although the mechanism of this unique reconstitution process is currently not fully understood, the finding points to a new possibility of using a nanometric space (<100 nm thick) as a platform for reconstituting and studying membrane proteins under the quasi-physiological conditions, which are difficult to be created by other methods.

Clinically Relevant Bacterial Outer Membrane Models for Antibiotic Screening Applications

Antibiotic resistance is a growing global health concern that has been increasing in prevalence over the past few decades. In Gram-negative bacteria, the outer membrane is an additional barrier through which antibiotics must traverse to kill the bacterium. In addition, outer membrane features and properties, like membrane surface charge, lipopolysaccharide (LPS) length, and membrane porins, can be altered in response to antibiotics and therefore, further mediate resistance. Model membranes have been used to mimic bacterial membranes to study antibiotic-induced membrane changes but often lack the compositional complexity of the actual outer membrane. Here, we developed a surface-supported membrane platform using outer membrane vesicles (OMVs) from clinically relevant Gram-negative bacteria and use it to characterize membrane biophysical properties and investigate its interaction with antibacterial compounds. We demonstrate that this platform maintains critical features of outer membranes, like fluidity, while retaining complex membrane components, like OMPs and LPS, which are central to membrane-mediated antibiotic resistance. This platform offers a non-pathogenic, cell-free surface to study such phenomena that is compatible with advanced microscopy and surface characterization tools like quartz crystal microbalance. We confirm these OMV bilayers recapitulate membrane interactions (or lack thereof) with the antibiotic compounds polymyxin B, bacitracin, and vancomycin, validating their use as representative models for the bacterial surface. By forming OMV bilayers from different strains, we envision that this platform could be used to investigate underlying biophysical differences in outer membranes leading to resistance, to screen and identify membrane-active antibiotics, or for the development of phage technologies targeting a particular membrane surface component.

Biomembranes in bioelectronic sensing

Cell membranes are integral to the functioning of the cell and are therefore key to drive fundamental understanding of biological processes for downstream applications. Here, we review the current state-of-the-art with respect to biomembrane systems and electronic substrates, with a view of how the field has evolved towards creating biomimetic conditions and improving detection sensitivity. Of particular interest are conducting polymers, a class of electroactive polymers, which have the potential to create the next step-change for bioelectronics devices. Lastly, we discuss the impact these types of devices could have for biomedical applications.

High-Resolution Nanopatterning of Free-Standing, Self-Supported Helical Polypeptide Rod Brushes via Electron Beam Lithography

In this study of nanopatterned helical poly(benzyl-l-glutamate) (PBLG) brushes, rod-type brush arrays were fabricated via an integrated process of high-resolution lithography and surface-initiated vapor deposition polymerization (SI-VDP). "Nanospikes" of polymer brushes with spacings of less than 100 nm were produced. The topology and areal behavior of the resulting patterned rod-like brushes were analyzed and compared with patterned coil-type brushes. A geometric study of these self-assembled "nanospikes" was carried out, and their cross sections were investigated via focused ion beam (FIB) and scanning electron microscopy (SEM). Furthermore, the presence of poly(N-isopropylacrylamide) (PNIPAM) brushes in unpatterned regions was shown to inhibit undesired "inter-spike" bridging of the PBLG brushes, resulting in more well-defined nanostructures. It was shown that rod-like polypeptide brushes are capable of self-segregation and become arranged vertically without any external support from their surroundings, to form a rod bundle end-point functional topography that could provide possible pathways for studies of model biological surfaces, directed assembly of nanoparticles, or binary mixed brush surfaces with dual properties.

Why Do Tethered-Bilayer Lipid Membranes Suit for Functional Membrane Protein Reincorporation?

Membrane proteins (MPs) are essential for cellular functions. Understanding the functions of MPs is crucial as they constitute an important class of drug targets. However, MPs are a challenging class of biomolecules to analyze because they cannot be studied outside their native environment. Their structure, function and activity are highly dependent on the local lipid environment, and these properties are compromised when the protein does not reside in the cell membrane. Mammalian cell membranes are complex and composed of different lipid species. Model membranes have been developed to provide an adequate environment to envisage MP reconstitution. Among them, tethered-Bilayer Lipid Membranes (tBLMs) appear as the best model because they allow the lipid bilayer to be decoupled from the support. Thus, they provide a sufficient aqueous space to envisage the proper accommodation of large extra-membranous domains of MPs, extending outside. Additionally, as the bilayer remains attached to tethers covalently fixed to the solid support, they can be investigated by a wide variety of surface-sensitive analytical techniques. This review provides an overview of the different approaches developed over the last two decades to achieve sophisticated tBLMs, with a more and more complex lipid composition and adapted for functional MP reconstitution.

Formation of Supported Lipid Bilayers Derived from Vesicles of Various Compositional Complexity on Conducting Polymer/Silica Substrates

Supported lipid bilayers (SLBs) serve important roles as minimalistic models of cellular membranes in multiple diagnostic and pharmaceutical applications as well as in the strive to gain fundamental insights about their complex biological function. To further expand the utility of SLBs, there is a need to go beyond simple lipid compositions to thereby better mimic the complexity of native cell membranes, while simultaneously retaining their compatibility with a versatile range of analytical platforms. To meet this demand, we have in this work explored SLB formation on PEDOT:PSS/silica nanoparticle composite films and mesoporous silica films, both capable of transporting ions to an underlying conducting PEDOT:PSS film. The SLB formation process was evaluated by using the quartz crystal microbalance with dissipation (QCM-D) monitoring, total internal reflection fluorescence (TIRF) microscopy, and fluorescence recovery after photobleaching (FRAP) for membranes made of pure synthetic lipids with or without the reconstituted membrane protein β-secretase 1 (BACE1) as well as cell-derived native lipid vesicles containing overexpressed BACE1. The mesoporous silica thin film was superior to the PEDOT:PSS/silica nanoparticle composite, providing successful formation of bilayers with high lateral mobility and low defect density even for the most complex native cell membranes.

Interaction between Bottlebrush Polymers and Phospholipid Membranes in Solutions

In this work, the interactions between bottlebrush polymers and phospholipid membranes were investigated using dissipative particle dynamics simulations. The weak and strong adsorption phenomena between the polymers and membranes were examined by calculating the system parameters. A spring model was introduced to explain the variances in the shape factors and the radius of gyration of the bottlebrush polymers, as well as the order parameters of the phospholipid membrane in the pulling processes. This work provides further understanding for the application of bottlebrush polymers in biological processes.

New Frontiers for Selective Biosensing with Biomembrane-Based Organic Transistors

Biosensing plays vital roles in multiple fields, including healthcare monitoring, drug screening, disease diagnosis, and environmental pollution control. In recent years, transistor-based devices have been considered to be valid platforms for fast, low-cost sensing of diverse analytes. Without additional functionalization, however, these devices lack selectivity; several strategies have been developed for the direct immobilization of bioreceptors on the transistor surface to improve detection capabilities. In this scenario, organic transistors have gained attention for their abilities to be coupled to biological systems and to detect biomolecules. In this Perspective, we discuss recent developments in organic-transistor-based biosensors, highlighting how their coupling with artificial membranes provides a strategy to improve sensitivity and selectivity in biosensing applications. Looking at future applications, this class of biosensors represents a breakthrough starting point for implementing multimodal high-throughput screening platforms.

Optical and Electronic Ion Channel Monitoring from Native Human Membranes

Transmembrane proteins represent a major target for modulating cell activity, both in terms of therapeutics drugs and for pathogen interactions. Work on screening such therapeutics or identifying toxins has been severely limited by the lack of available methods that would give high content information on functionality (ideally multimodal) and that are suitable for high-throughput. Here, we have demonstrated a platform that is capable of multimodal (optical and electronic) screening of ligand gated ion-channel activity in human-derived membranes. The TREK-1 ion-channel was expressed within supported lipid bilayers, formed via vesicle fusion of blebs obtained from the HEK cell line overexpressing TREK-1. The resulting reconstituted native membranes were confirmed via fluorescence recovery after photobleaching to form mobile bilayers on top of films of the polymeric electroactive transducer poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS). PEDOT:PSS electrodes were then used for quantitative electrochemical impedance spectroscopy measurements of ligand-mediated TREK-1 interactions with two compounds, spadin and arachidonic acid, known to suppress and activate TREK-1 channels, respectively. PEDOT:PSS-based organic electrochemical transistors were then used for combined optical and electronic measurements of TREK-1 functionality. The technology demonstrated here is highly promising for future high-throughput screening of transmembrane protein modulators owing to the robust nature of the membrane integrated device and the highly quantitative electrical signals obtained. This is in contrast with live-cell-based electrophysiology assays (e.g., patch clamp) which compare poorly in terms of cost, usability, and compatibility with optical transduction.

Self-Assembly of Mammalian-Cell Membranes on Bioelectronic Devices with Functional Transmembrane Proteins

Transmembrane proteins (TMPs) regulate processes occurring at the cell surface and are essential gatekeepers of information flow across the membrane. TMPs are difficult to study, given the complex environment of the membrane and its influence on protein conformation, mobility, biomolecule interaction, and activity. For the first time, we create mammalian biomembranes supported on a transparent, electrically conducting polymer surface, which enables dual electrical and optical monitoring of TMP function in its native membrane environment. Mammalian plasma membrane vesicles containing ATP-gated P2X2 ion channels self-assemble on a biocompatible polymer cushion that transduces the changes in ion flux during ATP exposure. This platform maintains the complexity of the native plasma membrane, the fluidity of its constituents, and protein orientation critical to ion channel function. We demonstrate the dual-modality readout using microscopy to characterize protein mobility by single-particle tracking and sensing of ATP gating of P2X2 using electrical impedance spectroscopy. This measurement of TMP activity important for pain sensing, neurological activity, and sensory activity raises new possibilities for drug screening and biosensing applications.

Facile Fabrication of Bio- and Dual-Functional Poly(2-oxazoline) Bottle-Brush Brush Surfaces

Poly(2-oxazoline)s (POx) bottle-brush brushes have excellent biocompatible and lubricious properties, which are promising for the functionalization of surfaces for biomedical devices. Herein, a facile synthesis of POx is reported which is based bottle-brush brushes (BBBs) on solid substrates. Initially, backbone brushes of poly(2-isopropenyl-2-oxazoline) (PIPOx) were fabricated via surface initiated Cu0 plate-mediated controlled radical polymerization (SI-Cu0 CRP). Poly(2-methyl-2-oxazoline) (PMeOx) side chains were subsequently grafted from the PIPOx backbone via living cationic ring opening polymerization (LCROP), which result in ≈100 % increase in brush thickness (from 58 to 110 nm). The resultant BBBs shows tunable thickness up to 300 nm and high grafting density (σ) with 0.42 chains nm-2 . The synthetic procedure of POx BBBs can be further simplified by using SI-Cu0 CRP with POx molecular brush as macromonomer (Mn =536 g mol-1 , PDI=1.10), which results in BBBs surface up to 60 nm with well-defined molecular structure. Both procedures are significantly superior to the state-of-art approaches for the synthesis of POx BBBs, which are promising to design bio-functional surfaces.

Boosting or moderating surface-initiated Cu(0)-mediated controlled radical polymerization with external additives

External additives regulate the copper disproportionation/comproportionation equilibrium to control polymer brush growth in surface-initiated Cu(0)-mediated controlled radical polymerization.

Interaction Mechanisms of Giant Unilamellar Vesicles with Hydrophobic Glass Surfaces and Silicone Oil-Water Interfaces: Adsorption, Deformation, Rupture, Dynamic Shape Changes, Internal Vesicle Formation, and Desorption

Phospholipid monolayers at oil-water interfaces are often obtained via vesicle adsorption. However, the interaction mechanisms of vesicles with these oil-water interfaces remain unclear. Herein, we studied the adsorption of giant unilamellar vesicles (GUVs) of approximately 2-5 μm diameter onto silicone oil-water interfaces and glass surfaces modified with hexamethyldisilazane (HMDS) and octadecyltrimethoxysilane (ODTMS) using fluorescence microscopy. The GUVs exhibited various modes of interaction, adsorbing on the silanized glass surfaces without sizable deformation, whereas GUVs bound to the silicone oil-water interface exhibited large deformation. After adsorption, GUV rupture occurred within 350, 110, and 3 ms on HMDS-modified glass, ODTMS-modified glass, and silicone oil-water interface, respectively. On glass surfaces, GUV rupture was often initiated and proceeded with pore formation near the surface. The monolayer patches formed by GUV rupture on HMDS-modified glass remained for at least 1 h over an area approximately twice of that estimated from the original GUV. On the ODTMS-modified glass and silicone oil surfaces, the monolayer patch structures disappeared in milliseconds owing to lipid diffusion across the interface. When adsorbed on the oil-water interface, the GUVs spontaneously underwent dynamic shape changes, internal vesicle formation, and desorption without rupture. Thus, it can be concluded that these different pathways arose from different lipid-surface affinities.

Facile Generation of Biomimetic-Supported Lipid Bilayers on Conducting Polymer Surfaces for Membrane Biosensing

Membrane biosensors that can rapidly sense pathogen interaction and disrupting agents are needed to identify and screen new drugs to combat antibiotic resistance. Bioelectronic devices have the capability to read out both ionic and electrical signals, but their compatibility with biological membranes is somewhat limited. Supported lipid bilayers (SLBs) have served as useful biomimetics for a myriad of research topics involving biological membranes. However, SLBs are traditionally made on inert, rigid, inorganic surfaces. Here, we demonstrate a versatile and facile method for generating SLBs on a conducting polymer device using a solvent-assisted lipid bilayer (SALB) technique. We use this bioelectronic device to form both mammalian and bacterial membrane mimetics to sense the membrane interactions with a bacterial toxin (α-hemolysin) and an antibiotic compound (polymyxin B), respectively. Our results show that we can form high quality bilayers of both types and sense these particular interactions with them, discriminating between pore formation, in the case of α-hemolysin, and disruption of the bilayer, in the case of polymyxin B. The SALB formation method is compatible with many membrane compositions that will not form via common vesicle fusion methods and works well in microfluidic devices. This, combined with the massive parallelization possible for the fabrication of electronic devices, can lead to miniaturized multiplexed devices for rapid data acquisition necessary to identify antibiotic targets that specifically disrupt bacterial, but not mammalian membranes, or identify bacterial toxins that strongly interact with mammalian membranes.

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

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

Constructing Supported Cell Membranes with Controllable Orientation

Membrane proteins play important roles in various cellular processes. Methods that can retain their structure and membrane topology information during their characterization are desirable for understanding their structure-function behavior. Here, we use giant plasma membrane vesicles (GPMVs) to form the supported cell membrane and develop a blotting method to control the orientation of the deposited cell membrane in order to study membrane proteins from either the extracellular or the cytoplasmic sides. We show that the membrane orientation can be retained in the directly-deposited membrane and the deposited membrane on mica can be blotted onto glass to reverse the membrane orientation. We used Aquaporin 3 (AQP3), an abundant native transmembrane protein in Hela cells, as a target to examine the cell membrane orientation in the directly-deposited and reversed membrane platforms. The immunostaining of antibodies targeting either the cyto-domain or ecto-domain of AQP3 shows that the intracellular side of the cell membrane faced the bulk aqueous environment when the GPMVs spontaneously ruptured on the support and that the membrane orientation was reversed after blotting. With this blotting method, we can thus control the orientation of the supported cell membrane to study membrane protein functions and structures from either side of the cell plasma membrane.

Surface-Initiated Cu(0)-Mediated CRP for the Rapid and Controlled Synthesis of Quasi-3D Structured Polymer Brushes

Surface-initiated controlled radical polymerization mediated by Cu(0) plate (SI-Cu(0)_plate-CRP) is an extremely effective and versatile technique for the synthesis of functional polymer brushes from vinyl monomers on planar substrates. The advantages of SI-Cu(0)_plate-CRP in comparison to "classical" SI-CRP methods not only rely on the easy accessibility, handling, and recycling of the catalyst source, but also on the faster brush growth rates, and exceptionally high reinitiation efficiencies and grafting densities for the obtained brushes. The confined geometry of the SI-Cu(0)_plate-CRP reaction setup, with a Cu(0) plate placed in close proximity to the initiator bearing substrate, considerably simplifies the preparation of polymer brushes over large areas, and the fabrication of gradient, patterned and arrayed polymer brushes. In this viewpoint we summarize the recent developments and applications of SI-Cu(0)_plate-CRP, emphasizing its mechanism, advantages, and standing challenges.

Single Virion Tracking Microscopy for the Study of Virus Entry Processes in Live Cells and Biomimetic Platforms

The most widely-used assays for studying viral entry, including infectivity, cofloatation, and cell-cell fusion assays, yield functional information but provide low resolution of individual entry steps. Structural characterization provides high-resolution conformational information, but on its own is unable to address the functional significance of these conformations. Single virion tracking microscopy techniques provide more detail on the intermediate entry steps than infection assays and more functional information than structural methods, bridging the gap between these methods. In addition, single virion approaches also provide dynamic information about the kinetics of entry processes. This chapter reviews single virion tracking techniques and describes how they can be applied to study specific virus entry steps. These techniques provide information complementary to traditional ensemble approaches. Single virion techniques may either probe virion behavior in live cells or in biomimetic platforms. Synthesizing information from ensemble, structural, and single virion techniques ultimately yields a more complete understanding of the viral entry process than can be achieved by any single method alone.