Biomedical subjects

Liangfang Zhang

Publications and source records attributed to Liangfang Zhang.

6 recordsLinked to original sources

PubMed2006

Nanoparticle-assisted surface immobilization of phospholipid liposomes.

Phospholipid liposomes (100-200 nm diameter) are deposited onto solid substrates after stabilizing them against fusion with the solid by allowing charged nanoparticles to adsorb at approximately 25% surface coverage. The immobilized vesicles remain stable over a period of days. Epifluorescence imaging shows that they diffuse freely over surfaces with the same charge but adsorb tightly onto surfaces with opposite charge. Nanoparticle adsorption to surface patterns of opposite charge provides a facile method to create large-scale surface-supported arrays of intact liposomes. This surface attachment method is simple chemically and applies generally for solid surfaces that can be hydrophobic or hydrophilic. Offering routes to localize proteins and other vesicle-contained objects at surfaces in tailored spatial patterns, these immobilized liposome arrays may find diverse applications in the emerging field of nanobiotechnology.

Adsorption↗

PubMed2006

Methods to track single-molecule trajectories.

Methods are discussed to track single molecules in planar-supported phospholipid bilayers. Mainly, these methods constitute optimizations for a low signal-to-noise ratio and for the dim optical characteristics of single molecules. Algorithmic modifications to compensate and correct for misidentifications and misassignments are also described. One key advance, which exchanges the typically fragmented reconstruction of the molecules' motion for more complete trajectories, is the incorporation of information about the molecules' past and future positions into the tracking. Although the main point of these methods is to aid in extending methods of object tracking to the single-molecule regime, they may also find use in other situations where the signal-to-noise ratio is low.

Journal Article↗

PubMed2006

Electrostatic stitching in gel-phase supported phospholipid bilayers.

We show that mixing zwitterionic lipids with up to 20% mole % cationic lipids produces gel-phase supported lipid bilayers that are morphologically free of defects detectable using noncontact mode atomic force microscopy (AFM). This contrasts with the observation of massive defects when anionic lipid was added, and also when no charged lipid was added. Infrared measurements of headgroup orientation in the presence of cationic lipid show that the mean headgroup orientation changes only minimally when temperature is lowered from the fluid phase to the gel phase. This is consistent with a tentative explanation, based on simple electrostatic arguments, in which cationic lipids "stitch" the bilayers together. On the functional side, this study demonstrates a simple method by which to minimize defects in gel-supported phospholipid bilayers.

Gels↗

PubMed2006

How to stabilize phospholipid liposomes (using nanoparticles).

The simple strategy of mixing phospholipid liposomes with charged nanoparticles and using sonication to mix them at low volume fraction produces particle-stabilized liposomes that repel one another and do not fuse. Subsequently, the volume fraction can be raised as high as approximately 50%, reversibly, still without fusion. In studies of liposome longevity, we verified the stability of particle-stabilized liposome suspensions with volume fraction up to 16% for up to 50 days, the longest period investigated. Fluorescent dyes were encapsulated within the particle-stabilized liposomes, without leakage. Although these particle-stabilized liposomes were stable against fusion, approximately 75% of the outer liposome surface remained unoccupied. This opens the door to using particle-stabilized liposomes in various applications.

Lipid Bilayers↗

PubMed2005

Lipid diffusion compared in outer and inner leaflets of planar supported bilayers.

The translational diffusion coefficient (D) of lipids located in the outer and inner leaflets of planar supported DLPC (1,2-dilauroyl-sn-glycero-3-phosphocholine) bilayers in the fluid phase was measured using fluorescence correlation spectroscopy of dye-labeled lipids at the low concentration of 0.001% and using iodide quenching of dyes in the outer leaflet to distinguish diffusion in the inner leaflet from that in the outer leaflet. To confirm the generality of these findings, the bilayers were prepared not only by vesicle fusion but also by Langmuir-Blodgett deposition. We conclude that regardless of whether the bilayers were supported on quartz or on a polymer cushion, D in the inner and outer leaflets was the same within an experimental uncertainty of +/-10% but with a small systematic tendency to be slower (by <5%) within the inner leaflet.

Biological Transport↗

PubMed2005

Slaved diffusion in phospholipid bilayers.

The translational diffusion of phospholipids in supported fluid bilayers splits into two populations when polyelectrolytes adsorb at incomplete surface coverage. Spatially resolved measurements using fluorescence correlation spectroscopy show that a slow mode, whose magnitude scales inversely with the degree of polymerization of the adsorbate, coexists with a fast mode characteristic of naked lipid diffusion. Inner and outer leaflets of the bilayer are affected nearly equally. Mobility may vary from spot to spot on the membrane surface, despite the lipid composition being the same. This work offers a mechanism to explain how nanosized domains with reduced mobility arise in lipid membranes.

Biophysics↗