4 research outputs found
Change of Line Tension in Phase-Separated Vesicles upon Protein Binding
We measured the effect of a model membrane-binding protein
on line
tension and morphology of phase-separated lipid-bilayer vesicles.
We studied giant unilamellar vesicles composed of a cholesterol/dioleoylphosphatidylcholine/palmitoylsphingomyelin
mixture and a controlled mole fraction of a Ni-chelating lipid. These
vesicles exhibited two coexisting fluid-phase domains at room temperature.
Owing to the line tension, σ, between the two phases, the boundary
between them was pulled like a purse string so that the smaller domain
formed a bud. While observing the vesicles in a microscope, histidine-tagged
green fluorescent protein was added, which bound to the Ni-chelating
lipid. As protein bound, the vesicle shape changed and the length
of the phase boundary increased. The change in morphology was attributed
to a reduction of σ between the two phases because of preferential
accumulation of histidine-tagged green fluorescent protein–Ni-chelating
lipid clusters at the domain boundary. Greater reductions of σ
were found in samples with higher concentrations of Ni-chelating lipid;
this trend provided an estimate of the binding energy at the boundary,
approximately <i>k</i><sub>B</sub><i>T</i>. The
results show how domain boundaries can lead to an accumulation of
membrane-binding proteins at their boundaries and, in turn, how proteins
can alter line tension and vesicle morphology
Wax Spreading in Paper under Controlled Pressure and Temperature
This
work describes a novel rapid method to fabricate high-resolution
paper-based microfluidic devices using wax-ink-based printing. This
study demonstrates that both temperature and pressure are important
knobs in controlling the device resolution. High-resolution lines
and patterns were obtained by heating the paper asymmetrically from
one side up to 110 °C while applying pressure up to 49 kPa. Starting
with wax lines with an initial width of 130 μm, we achieve a
thorough penetration through a 190 μm-thick paper with lateral
spreading on the front as narrow as 90 μm. The role of temperature
and pressure are systematically studied and compared with the prediction
of the Lucas–Washburn equation. We found that the temperature
dependence of spreading can be explained by the viscosity change of
the wax, according to the Lucas–Washburn equation. The pressure
dependence deviates from Lucas–Washburn behavior because of
compression of the paper. An optimal condition for achieving full
depth penetration of the wax yet minimizing lateral spreading is suggested
after exploring various parameters including temperature, pressure,
and paper type. These findings could lead to a rapid roll-to-roll
fabrication of high-resolution paper-based diagnostic devices
Confined Assemblies of Colloidal Particles with Soft Repulsive Interactions
We investigate the microconfinement
of charged silica nanoparticles
dispersed in refractive index matching monomers in polyÂ(dimethylsiloxane)
(PDMS) porous membrane. Here, the silica colloidal particles interact
with each other and the pore wall via electrostatic double layer forces.
Different from the hard sphere systems where the assembled morphologies
are prescribed by the diameter ratio between the cylindrical confinement
and the nanoparticles, here we observe a much richer variety of assemblies
that are highly sensitive to both bulk and local nanoparticle concentration
with fixed particle size and channel size. The experimentally observed
assembly morphologies are consistent with theoretical predictions
from the literature, based on Yukawa potential in the low packing
density regime. Also, most of the configurations found in the experiment
are well described by computer simulations using pairwise additive
long-range repulsive interactions, demonstrating the ability to control
the system to obtain a desired structure
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