Elucidating How Bamboo Salt Interacts with Supported Lipid Membranes:
Influence of Alkalinity on Membrane Fluidity
Supporting Information
Jong Hee Jeong+,6, Jae-Hyeok Choi+,1,2, Min Chul Kim+,1,2, Jae Hyeon Park1,2, Jason Scott
Herrin1, Seung Hyun Kim5, Haiwon Lee4,6, Nam-Joon Cho*,1,2, 3
1
School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang
Avenue 639798, Singapore
2
Centre for Biomimetic Sensor Science, Nanyang Technological University, 50 Nanyang Drive
637553, Singapore
3
School of Chemical and Biomedical Engineering, Nanyang Technological University, 62
Nanyang Drive 637459, Singapore
4
Department of Chemistry, College of Natural Science, Hanyang University, Seoul 133791,
Korea
5
Department of Neurology, College of Medicine, Hanyang University 133791, Seoul, Korea
6
Department of Convergence Nanoscience, College of Natural Science, Hanyang University,
Seoul 133070, Korea
+
The authors contributed equally to this work.
*Corresponding author.
E-mail: njcho@ntu.edu.sg
1
Extended-DLVO Model Calculation Method
The general method of our model calculations is based on the work by Jackman et al.1 A full
description of the equations used to calculate the van der Waals, double-layer electrostatic, and
hydration interaction energies is presented in the corresponding reference. In contrast to the
previous work focused on titanium oxide, we consider here a supported lipid bilayer on silicon
oxide and a summary table of the parameters used in our modeling calculations is presented
below:
Medium
SiO2 (Ref. 2)
Lipid (Ref. 2)
Water (Ref. 2)
Dielectric
Constant
3.8
2.04
77.6
Oscillator
Parameter
1.098
1.041
0.762
Absorption
Frequency (UV)
3.21×1015
2.64×1015
3.17×1015
Av=0 (J)
Av>0 (J)
2.67×10-21
1.99×10-21
The inverse Debye length for our system is calculated by
𝜀 𝜀 𝑘 𝑇
𝑟 0 𝐵
𝜅 −1 = √ 2𝑁
𝑒2𝐼
𝐴
(1)
I is the ionic strength of electrolyte in the units of mol/m3, e.g., 150 mol/m3 in the model
calculations. As an example, for 150 mM monovalent salt, the calculated inverse Debye length
would 1.2805 nm-1.
2
Figure Legend
Table S1. Summary of Surface Potentials Used in Double-Layer Electrostatic Force
Calculations. Zeta potential measurements of zwitterionic lipid vesicles were originally
performed in 10 mM NaCl aqueous salt solution (Fig. 1 from Ref. 3). To a first approximation4,
the zeta potential values are assumed to be equal to the corresponding surface potential values
and electrostatic shielding is also accounted for by Eq. (10) from Nabika et al.5. An ionic
strength corresponding to 150 mM monovalent salt solution was used in the calculations because
similar conditions were used in previous experimental works6, 7 and the condition is also similar
to the experimental work in the present study. A similar approach was employed for silicon
oxide surfaces using values obtained from Ref. 8.
Figure S1. QCM-D Characterization of Supported Lipid Bilayer. 0.2 mg/mL POPC lipid
vesicles in 10 mM Tris buffer [pH 7.5] with 150 mM NaCl were added at t=5 min to a silicon
oxide surface, leading to supported lipid bilayer formation. At t=25 min, a solution-exchange
was performed in order to introduce bamboo salt solution of varying ionic strength. At t=38 min,
another solution-exchange was performed in order to introduce Tris buffer solution which is
equivalent to the solution used in the first step. Each panel presents buffer-exchange with the
following ionic strength of bamboo salt solution: (A) 150 mM; (B) 1000 mM; (C) 2000 mM; and
(D) 3750 mM.
Figure S2. Influence of Ionic Strength on the Fluidity of a Supported Lipid Bilayer on
Glass. Epifluorescence microscopy was performed in order to visualize supported lipid bilayers
in bamboo salt solutions prepared with the commercial product, Sample One. Panels A-D present
time-lapsed fluorescence micrographs of supported lipid bilayers incubated in alkaline pH 10
Tris buffer solutions of varying ionic strength. Photobleaching was performed at t=0 min, and
3
bleached spot corresponds to the dark spot in the center of the micrograph. The left and right
micrographs correspond to snapshots recorded at t=0 and t=90 sec, respectively. The
fluorescence intensity as a function of distance across the bleached spot at the two times is
presented below the micrographs.
Figure S3. Influence of Ionic Strength on the Fluidity of a Supported Lipid Bilayer on
Glass. Epifluorescence microscopy was performed in order to visualize supported lipid bilayers
in bamboo salt solutions prepared with the commercial product, Sample Two.
Figure S4. Influence of Ionic Strength on the Fluidity of a Supported Lipid Bilayer on
Glass. Epifluorescence microscopy was performed in order to visualize supported lipid bilayers
in bamboo salt solutions prepared with the commercial product, Sample Three.
Figure S5. Influence of Ionic Strength on the Fluidity of a Supported Lipid Bilayer on
Glass. Epifluorescence microscopy was performed in order to visualize supported lipid bilayers
in alkaline pH 10 Tris buffer solution.
Figure S6. van der Waals Interaction Energy as a Function of Separation Distance. Curves
are presented corresponding to lipid bilayer on silicon oxide under varying ionic strength
conditions.
Figure S7. Double-Layer Electrostatic Interaction Energy as a Function of Separation
Distance. Curves are presented corresponding to lipid bilayer on silicon oxide under varying
ionic strength conditions.
Figure S8. Hydration Interaction Energy as a Function of Separation Distance. In the model
calculations, different values corresponding to the decay length of the hydration force for a lipid
bilayer on silicon oxide were tested, including (A) 0.15 and (B) 0.25 nm.
4
Table S1
Ionic Strength
(mM)
150
300
500
1000
2000
3750
SiO2 Surface Potential
(mV)
-21
-14.9
-11.5
-8.1
-5.8
-4.2
5
Vesicle Surface Potential
(mV)
-6
-4.2
-3.3
-2.3
-1.6
-1.2
Figure S1
BS
0
4
-10
3
-20
2
-30
1
-40
0
-50
Frequency (Hz)
BS
50
-1
15
10
20
30
Time (min)
40
-20
-30
-40
0
40
BS
R
50
R
50
40
-30
-60
-90
-20
30
-25
25
-30
20
-35
15
-40
10
-50
30
20
5
-45
-150
6
20
30
Time (min)
IB VLB
0
-120
50
10
10
0
10
20
30
40
50
0
0
10
20
30
Time (min)
40
50
-6
0
-10
D
20
5
10
9
8
7
6
5
4
3
2
1
0
-1
R
0
-60
25
R
BS
R
Energy Dissipation (10 )
R
40
-6
10 IB VLB
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
0
10
20
30
Time (min)
IB VLB
-6
10
Energy Dissipation (10 )
C
0
10
-50
-6
-60
B
5
R
Frequency (Hz)
R
Frequency (Hz)
Frequency (Hz)
IB VLB
Energy Dissipation (10 )
10
Energy Dissipation (10 )
A
Figure S2
7
Figure S3
8
Figure S4
9
Figure S5
10
Figure S6
11
Figure S7
12
Figure S8
13
Supporting Information References
1.
2.
3.
4.
5.
6.
7.
8.
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