Surface-immobilized vesicle

Chemical reactions occurring in geometries resembling those found in a cell can be investigated with the help of nanotube-vesicle networks (NVNs, Fig. 23.3 [fO]). NVNs are highly flexible lipid bilayer structures in which the main building blocks are surface-immobilized vesicles connected by nanotubes. 

Lipid bilayers and surface immobilized vesicles provide an alternative architecture for the micro- and nanofabrication of bioreactive and biocompatible platforms [63-67]. In recent years, the modification of solid surfaces with biological molecules has been widely studied as a means to obtain biomimetic interfaces for biomedical and environmental applications. Among the various formats of functionalized interfaces investigated, substrate-supported lipid bilayers have received considerable attention. Proteins have been successfully... 

Biotinylated liposomes usually are created by modification of PE components with an amine-reactive biotin derivative, for example NHS-LC-Biotin (Chapter 11, Section 1). The NHS ester reacts with the primary amine of PE residues, forming an amide bond linkage (Figure 22.19). A better choice of biotinylation agent may be to use the NHS-PEG -biotin compounds (Chapter 18), because the hydrophilic PEG spacer provides better accessibility in the aqueous environment than a hydrophobic biotin spacer. Since the modification occurs at the hydrophilic end of the phospholipid molecule, after vesicle formation the biotin component protrudes out from the liposomal surface. In this configuration, the surface-immobilized biotins are able to bind (strept)avidin molecules present in the outer aqueous medium. 

The hposome inside a hposome configuration is analogous to a vesicle inside a secretory cell during the last stages of the release process. Microelectroporation (77) assisted insertion and careful micromanipulation of a micropipette is required for formation of the artificial cell. Briefly, a micropipette filled with the redox molecule of choice (typically catechol) is positioned next to a surface immobilized giant unilamellar vesicle (GUV) with... 

Figure 6.14 (A) Scheme of an immobilized vesicle on a surface. LSM images of structurally immobilized nanoreactors (B) before and (C) after incubation (20 minutes) with ELF 97 substrate.

Polymerization is found assisting the immobilization of carbonic anhydrase on the surface of vesicles. In these examples, polymerization is stabilizing the vesicular structures as well as eliminating the motional properties of lipids i.e., lateral mobility and rotational motion. This explains the poor immobilization of enzyme on polymerized vesicles containing non-polymerizable metal chelating lipid. Detailed studies on the kinetics of enzyme binding with non-polymerizable metal-chelated lipid inserted in polymer constrained environment of polymerized vesicles may provide an insight about the role of polymerization on enzyme immobilization. 

Fig. 9 Surface modification of cells with ssDNA-PEG-lipid. (a) Real-time monitoring of PEG-lipid incorporation into a supported lipid membrane by SPR. (r) A suspension of small unilamellar vesicles (SUV) of egg yolk lecithin (70 pg/mL) was applied to a CH3-SAM surface. A PEG-lipid solution (100 pg/mL) was then applied, (ii) Three types of PEG-lipids were compared PEG-DMPE (C14), PEG-DPPE (C16), and PEG-DSPE (C18) with acyl chains of 14, 16, and 18 carbons, respectively, (b) Confocal laser scanning microscopic image of an CCRF-CEM cell displays immobilized FITC-oligo(dA)2o hybridized to membrane-incorporated oligo(dT)20-PEG-lipid. (c) SPR sensorigrams of interaction between oligo(dA)2o-urokinase and the oligo (dT)2o-PEG-lipid incorporated into the cell surface, (i) BSA solution was applied to block nonspecific sites on the oligo(dT)20-incorporated substrate, (ii) Oligo(dA)20-urokinase (solid line) or oligo(dT)20-urokinase (dotted line) was applied...

Boukobza, E., Sonnenfeld, A., and Haran, G. (2001). Immobilization in surface-tethered lipid vesicles as a new tool for single biomolecule spectroscopy. J. Phys. Chem. B 105, 12165-12170. 

Alternative approaches for liposome assembhes have also been demonstrated, where histidine-tagged hpids have been introduced in vesicles, which were then anchored to chelator surfaces [39,51]. Similarly, oligonucleotide-modified lipids can be incorporated in the vesicles and bind to complementary sequences immobilized on the sensor surface [52,53]. The latter strategy can also be utilized for spatially resolved immobihzations. 

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