Chemistry Reference
In-Depth Information
Fig. 4.4
Two lipidmonolayers are brought together by controlled pumping through themicrofluidic
channel. The contrast between the aqueous and oil phase can be clearly seen in the leftmost image.
The structure in the dashed box is of interest in the current investigation. The scale bar is 50 microns
point-like, also called micro-focus, lab sources various approaches are presented in
literature [
34
-
36
].
4.3.3 Data Analysis and Fitting
The images resulting from the process of lipid membrane formation by bringing two
oil-water interfaces are shown in Fig.
4.4
. It can already be seen that a single oil-
water interface decorated by a lipid monolayer leads to a significant phase contrast.
While the diffraction due to this single lipid monolayer can be analysed using an
asymmetric phase slit model [
37
], the focus of this present investigation is the lipid
membrane. The diffraction pattern due to such a membrane can also be seen with
a maximum in the center with symmetric peaks on either side of this maxima. This
is to be expected from the symmetry of the bilayer structure that is formed in the
microfluidic channel.
From such an image, a one-dimensional profile of the diffraction intensity is
constructed by taking an average over a certain region of interest as shown in Fig.
4.5
.
Data fitting is then performed in MatLab using a
2
-minimization algorithm called
“Nelder-Mead simplex method” [
38
]. The image formation, as described earlier
is determined by a few main parameters viz. the thickness of the lipid membrane
d
, the refractive index difference
χ
and the effective propagation distance
z
eff
.
While the difference in the refractive indices
δ
δ
=
δ
BLM
−
δ
H
2
0
is calculated
using the literature electron density values of water, solvent, and lipids, giving
δ
∼
10
−
7
. The propagation distance
z
eff
is defined by the experimental setup as
discussed earlier. The computational details and the source codes of the algorithms
used in the fitting procedure are described in an earlier thesis [
37
].
−
1
.
23
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