Activation of G-protein-coupled receptors in cell-derived plasma membranes supported on porous beads

The ATTO 565 Dye and Its Applications in Microscopy

ATTO 565, a Rhodamine-type dye, has garnered significant attention due to its remarkable optical properties, such as a high fluorescence quantum yield, and the fact that it is a relatively stable structure and has low biotoxicity. ATTO 565 has found extensive applications in combination with microscopy technology. In this review, the chemical and optical properties of ATTO 565 are introduced, along with the principles behind them. The functionality of ATTO 565 in confocal microscopy, stimulated emission depletion (STED) microscopy, single-molecule tracking (SMT) techniques, two-photon excitation-stimulated emission depletion microscopy (TPE-STED) and fluorescence correlation spectroscopy (FCS) is discussed. These studies demonstrate that ATTO 565 plays a crucial role in areas such as biological imaging and single-molecule localization, thus warranting further in-depth investigations. Finally, we present some prospects and concepts for the future applications of ATTO 565 in the fields of biocompatibility and metal ion detection. This review does not include theoretical calculations for the ATTO 565 molecule.

Supported Cell Membrane Sheets to Monitor Protein Assembly

Studying protein-protein and protein-lipid interactions in their native environment is highly desirable, yet, the heterogeneity and complexity of cellular systems limits the repertoire of experimental methods available. In cells, interactions are often taking place in confined microenvironments where factors such as avidity, hindered diffusion, reduced dimensionality, crowding etc. strongly influence the binding kinetics and therefore it can be problematic to equate binding affinities obtained by bulk in-solution methods (e.g., Fluorescence Polarization, Isothermal titration calorimetry, Microscale thermophoresis) with those occurring in real cellular environments. The Supported Cell Membrane Sheet method presented here, addresses these issues by allowing access to the inner leaflet of the apical plasma membrane. The method is a highly versatile, near-native platform for both qualitative and quantitative studies of protein-protein and protein-lipid interactions occurring directly in or on the plasma membrane.

Nanohole array plasmonic biosensors: Emerging point-of-care applications

Point-of-care (POC) applications have expanded hugely in recent years and is likely to continue, with an aim to deliver cheap, portable, and reliable devices to meet the demands of healthcare industry. POC devices are designed, prototyped, and assembled using numerous strategies but the key essential features that biosensing devices require are: (1) sensitivity, (2) selectivity, (3) specificity, (4) repeatability, and (5) good limit of detection. Overall the fabrication and commercialization of the nanohole array (NHA) setup to the outside world still remains a challenge. Here, we review the various methods of NHA fabrication, the design criteria, the geometrical features, the effects of surface plasmon resonance (SPR) on sensing as well as current state-of-the-art of existing NHA sensors. This review also provides easy-to-understand examples of NHA-based POC biosensing applications, its current status, challenges, and future prospects.

Formation of biomembrane microarrays with a squeegee-based assembly method

Lipid bilayer membranes form the plasma membranes of cells and define the boundaries of subcellular organelles. In nature, these membranes are heterogeneous mixtures of many types of lipids, contain membrane-bound proteins and are decorated with carbohydrates. In some experiments, it is desirable to decouple the biophysical or biochemical properties of the lipid bilayer from those of the natural membrane. Such cases call for the use of model systems such as giant vesicles, liposomes or supported lipid bilayers (SLBs). Arrays of SLBs are particularly attractive for sensing applications and mimicking cell-cell interactions. Here we describe a new method for forming SLB arrays. Submicron-diameter SiO2 beads are first coated with lipid bilayers to form spherical SLBs (SSLBs). The beads are then deposited into an array of micro-fabricated submicron-diameter microwells. The preparation technique uses a "squeegee" to clean the substrate surface, while leaving behind SSLBs that have settled into microwells. This method requires no chemical modification of the microwell substrate, nor any particular targeting ligands on the SSLB. Microwells are occupied by single beads because the well diameter is tuned to be just larger than the bead diameter. Typically, more 75% of the wells are occupied, while the rest remain empty. In buffer SSLB arrays display long-term stability of greater than one week. Multiple types of SSLBs can be placed in a single array by serial deposition, and the arrays can be used for sensing, which we demonstrate by characterizing the interaction of cholera toxin with ganglioside GM1. We also show that phospholipid vesicles without the bead supports and biomembranes from cellular sources can be arrayed with the same method and cell-specific membrane lipids can be identified.

Downscaling the analysis of complex transmembrane signaling cascades to closed attoliter volumes

Cellular signaling is classically investigated by measuring optical or electrical properties of single or populations of living cells. Here we show that ligand binding to cell surface receptors and subsequent activation of signaling cascades can be monitored in single, (sub-)micrometer sized native vesicles with single-molecule sensitivity. The vesicles are derived from live mammalian cells using chemicals or optical tweezers. They comprise parts of a cell's plasma membrane and cytosol and represent the smallest autonomous containers performing cellular signaling reactions thus functioning like minimized cells. Using fluorescence microscopies, we measured in individual vesicles the different steps of G-protein-coupled receptor mediated signaling like ligand binding to receptors, subsequent G-protein activation and finally arrestin translocation indicating receptor deactivation. Observing cellular signaling reactions in individual vesicles opens the door for downscaling bioanalysis of cellular functions to the attoliter range, multiplexing single cell analysis, and investigating receptor mediated signaling in multiarray format.

High-density arrays of submicron spherical supported lipid bilayers

Lipid bilayer membranes found in nature are heterogeneous mixtures of lipids and proteins. Model systems, such as supported lipid bilayers (SLBs), are often employed to simplify experimental systems while mimicking the properties of natural lipid bilayers. Here, we demonstrate a new method to form SLB arrays by first forming spherical supported lipid bilayers (SSLBs) on submicrometer-diameter SiO(2) beads. The SSLBs are then arrayed into microwells using a simple physical assembly method that requires no chemical modification of the substrate nor modification of the lipid membrane with recognition moieties. The resulting arrays have submicrometer SSLBs with 3 μm periodicity where >75% of the microwells are occupied by an individual SSLB. Because the arrays have high density, fluorescence from >1000 discrete SSLBs can be acquired with a single image capture. We show that 2-component random arrays can be formed, and we also use the arrays to determine the equilibrium dissociation constant for cholera toxin binding to ganglioside GM1. SSLB arrays are robust and are stable for at least one week in buffer.