Interaction of Multiwalled Carbon Nanotubes with
Model Cell Membranes: A QCM-D Study
PENG YI and Kai Loon Chen (PI)
Department of Geography and Environmental Engineering
Johns Hopkins University
1
OverviewBackground and objectivePreparation and characterization of multi-walled carbon nanotubes (MWNTs)Deposition kinetics of MWNTs on SLBsReversibility of MWNT deposition on SLBsAttachment of MWNTs to phospholipid vesiclesConclusions
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Carbon Nanotubes (CNTs)
www.basesciences.commrbarlow.wordpress.com
Single-walled carbon nanotubes
(SWNTs)
Multiwalled carbon nanotubes(MWNTs)
3
Applications of Carbon Nanotubes
Mechanical properties: high strength; light weight
Electronic properties: semiconducting or metallic
Cao et al., Nature, 2008, 495-500
phys.org
4
Potential Release of Carbon Nanotubes
Consumer products which contain CNTsFactories producing CNTs and CNT-based productsWaste disposal facilities, e.g., incinerators and landfills
Potential Routes of Release
–COOH
–OH
=O
CNTs can be oxidized in natural and engineered environments
5
Toxicity of Carbon NanotubesCause respiratory toxicity in rats
Inactivate microorganisms
Kang et al., Langmuir2007, 8670-8673
Muller et al., Toxicology and Applied Pharmacology 2005, 221-231
2 mg MWNTs/rat granulomas
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Toxicity of Carbon NanotubesInduce apoptosis of human epidermal keratinocytes
Shvedova et al., Journal of Toxicology & Environmental Health , Part A, 2003, 1909-1926
Monteiro-Riviere et al., Toxicology Letters, 2005, 377-384
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Interaction of CNTs with Cell Membranes
Sylvia S. Mader, Biology, 9th ed., 2007, McGraw-Hill Companies, Inc.
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Recent Research on Adsorption of Nanoparticles on Model Cell Membranes
C60 fullerol pH 3
pH 4
pH 5
pH 7.4
pH 5
pH 7.4
Hou et al., Langmuir, 2011, 11899-11905
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Objective
To investigate the influence of solution chemistry on deposition and remobilization of MWNTs on model cell membranes
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Oxidization and Characterization of MWNTs
Expose pristine MWNTs to a 3:1 acid mixture of 98% H2SO4 and 69% HNO3The distribution of oxygen-containing functional groups was quantified by X-ray photoelectron spectroscopy in conjunction with vapor phase chemical derivatization
O (Total) O(C-OH) O(COOH) O(C=O) O(Others)0
2
4
6
8
10
12A
tom
ic P
erce
ntag
e o
f Oxy
gen
(%)
Oxygen-Containing Functional Groups
Yi and Chen, Langmuir 2011,27, 3588–3599.
–COOH
–OH
=O
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Preparation of MWNT Stock Suspensions
Sonication
Centrifugation
20 hours
5 mins,1400 RCF
Supernatant
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Electrokinetic Properties of MWNTs in NaCl and CaCl2 Solutions
Electrophoretic mobility (EPM)
Brookhaven ZetaPALSAt pH 7.3, most carboxyl
groups are expected to be deprotonated
0.1 1 10 100-4
-3
-2
-1
0
EP
M (1
0-8m
2 /Vs)
Electrolyte Concentration (mM)
CaCl2 NaCl
37 CpH 7.3
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Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D)
Laminar flow at 0.6 mL/min[MWNT] = ca. 0.5 mg/LT = 37 ºC, pH = 7.3 or 2.0
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Principle of QCM-DFrequency and Dissipation
Generally, the frequency decreases as the deposited mass on the crystal increases
The dissipation increases as the softness of the deposited layer increases
A(t)=A0exp(-t/)sin(2ft+)
D=1/f
Time
Amplitude
From qsense
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Preparation of Vesicle Suspensions
From Avanti Polar Lipids, Inc.http://www.avantilipids.com/
HEPES buffer (10 mM HEPES, 150 mM NaCl, pH 7.4)
Chloroform
Dry under vacuum
Extrusion through50-nm membrane
90 nm in diameter
DOPC:(1,2-dioleoyl-sn-glycero-3-
phosphocholine)
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Preparation of Vesicle Suspensions
From Avanti Polar Lipids, Inc.http://www.avantilipids.com/ 17
Electrophoretic Mobilities of DOPC Vesicles
0.1 1 10 100-2
-1
0
1
2
EP
M (1
0-8m
2 /Vs)
Electrolyte Concentration (mM)
CaCl2 NaCl
37 CpH 7.3 The surface charge of
vesicles approaches neutral at high NaCl concentrations
The surface charge of vesicles is reversed when CaCl2 concentration is above 0.5 mM
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Formation of SLBs on Silica-coated QCM-D Crystals
0 5 10 15 20 25-60
-50
-40
-30
-20
-10
0
10
20
HEPES buffer DOPC liposomes (formation of SLB)HEPES buffer
Frequency Dissipation
Time (min)
Freq
uenc
y S
hift,
f (5
)(Hz)
DI water
-2
0
2
4
6
8
10
12
14
Dis
sipa
tion
Shi
ft,
D(5
)(10-6
)
T = 37 ºCpH = 7.3
Cartoons are from qsensehttp://www.qsense.com/ 19
Formation of SLBs on Silica Wafer
Richter et al., Biophysical Journal, 2003, 3035-3047
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Deposition of MWNTs on SLBs
70 80 90 100 110 120-32
-30
-28
-26
-24
-22
-20
MWNT deposition on SLBs at 3 mM CaCl2
3 mM CaCl2
Time (min)
Freq
uenc
y S
hift,
f (5
)(Hz)
dtdf )5(
The decrease of frequency is proportional to the mass of deposited MWNTs
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Deposition Rates of MWNTs on DOPC SLBsin the presence of CaCl2 at pH 7.3
SLB (–)Silica (–)
0.1 1 100.0
0.2
0.4
0.6
0.8
|df
(5)/d
t| (H
z/m
in)
CaCl2 Concentration (mM)
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Deposition Rates of MWNTs on PLL-modified Surfaces in CaCl2 at pH 7.3
PLL (+)Silica (–)
0.1 1 100.00.20.40.60.81.01.21.4
|d
f (5)/d
t| (H
z/m
in)
CaCl2 Concentration (mM)
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0.1 1 100.1
1
Atta
chm
ent E
ffici
ency
CaCl2 Concentration (mM)
Deposition Kinetics of MWNTs on SLBsin the presence of CaCl2
fav
dtdfdtdf
//
)5(
)5(
Attachment Efficiency:
α is the fraction of collision between CNTs and membrane surfaces that will result in permanent attachment. 24
Deposition Kinetics of MWNTs on SLBsin the presence of CaCl2
fav
dtdfdtdf
//
)5(
)5(
Attachment Efficiency:
0.1 1 100.1
1
Atta
chm
ent E
ffici
ency
CaCl2 Concentration (mM)
critical deposition concentration = 0.46 mM
Unfavorable Favorable
EDL and van der Waals interactions
Charge reversal of SLBs when CaCl2 concentration is higher than CDC 25
Deposition Kinetics of MWNTs on SLBsin the presence of NaCl
fav
dtdfdtdf
//
)5(
)5(
Attachment Efficiency:
The EPM of DOPC vesicles at 70 mM NaCl was close to zero. Thus, electrostatic repulsion was not the dominant interaction
Headgroups of DOPC lipids are strongly hydrophilic. Water can strongly bind to the exposed headgroups of the DOPC SLBs and result in repulsive hydration forces
100 10000.1
1
Atta
chm
ent E
ffici
ency
NaCl Concentration (mM)
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Effect of pH on Deposition Kinetics of MWNTs on DOPC SLBs
0 5 10 15 20 25 30 35-10
-8
-6
-4
-2
0
2
1 mM NaCl, pH 2.0
Time (min)
Freq
uenc
y S
hift,
f (5
)(Hz) 1 mM NaCl, pH 7.3
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Effect of pH on Deposition Kinetics of MWNTs on DOPC SLBs
0 5 10 15 20 25 30 35-10
-8
-6
-4
-2
0
2
1 mM NaCl, pH 2.0
Time (min)
Freq
uenc
y S
hift,
f (5
)(Hz) 1 mM NaCl, pH 7.3
pH 2.0 pH 7.3-4-3-2-10123
EP
M (1
0-8m
2 /Vs)
DOPC vesicles MWNTs
1 mM NaCl
Deposition of MWNTs is favorable at pH 2.0 because MWNTs and SLBs are oppositely charged
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Independence of Attachment Efficiency on Electrolyte Concentration at pH 2.0
Deposition of MWNTs is favorable at pH 2.0 because MWNTs and SLBs are oppositely charged
1 mM N
aCl
150 m
M NaC
l0.0
0.5
1.0
1.5
NaCl Concentration
Atta
chm
ent E
ffici
ency
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0 20 40 60 80 100-12
-10
-8
-6
-4
-2
0
2
DI water (pH 7.3)
1 M CaCl2
1 mM CaCl2
1 mM CaCl2
CNT deposition on SLBs at 1 mM CaCl2
Time (min)
Freq
uenc
y S
hift,
f (5
)(Hz)
Reversibility of MWNT Deposition on DOPC SLBs at Decreased Electrolyte Concentration
12%25%
SLBs became negatively charged when CaCl2concentration decreased from 1 mM to 1μM
Electrostatic attraction became electrostatic repulsion which resulted in the release of MWNTs
The incomplete release may be due to the surface-charge heterogeneity of MWNTs
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0 10 20 30 40 50 60 70-12
-10
-8
-6
-4
-2
0
2 1 mM NaCl (pH 7.3)
1 mM NaCl (pH 2)
Freq
uenc
y S
hift,
f (5
)(Hz)
Time (min)
1 mM NaCl (pH 2)
CNT deposition on SLBs at 1 mM NaCl (pH 2)
Reversibility of MWNT Deposition on DOPC SLBs at Increased pH
19%
SLBs became negatively charged when pH increased from 2.0 to 7.3
The electrostatic repulsion between both negatively charged MWNTs and SLBs lead to the release of MWNTs
The deposited MWNTs were only partially released due to surface-charge heterogeneity of MWNTs
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Attachment of MWNTs on Supported Vesicular Layer
0 50 100 150
-200
-150
-100
-50
0
MWNT depositionat 1 mM CaCl2, pH 7.3
1 mM CaCl2
pH 7.3HEPES buffer
HEPES buffer
Time (min)
Freq
uenc
y S
hift,
f (5
)(Hz)
0
20
40
60
Deposition of DOPC vesicles on gold surface
Dis
sipa
tion
Shi
ft,
D(5
)(10-6
)
Gold-coated crystal
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Cryogenic TEM Imaging of MWNT-Vesicle Suspensions
50 nm (b)
(a)200 nm
MWNTs had aggregated with DOPC vesicles in a 1 mM CaCl2 and pH 7.3 solution for ca. 20 min before cryo-TEM images were taken
Deformation of vesicles was observed upon attachment on MWNTs
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Concluding RemarksDeposition kinetics of MWNTs on DOPC SLBs in the presence of CaCl2 are governed by EDL and van der Waals forcesIn the presence of NaCl, hydration force seems to play an important role in controlling the deposition kinetics of MWNTs on DOPC SLBsThe MWNTs deposited on SLBs are mostly irreversible when rinsed with a low-ionic-strength and pH 7.3 solutionInteractions between MWNTs and supported vesicles resulted in no significant damage to vesicular integrityFurther studies will be conducted on CMP nanoparticles, namely, ceria, silica, and alumina nanoparticles
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Acknowledgements
Prof. Howard Fairbrother and Drs. Billy Smith and Kevin Wepasnick from Department of Chemistry, JHUSemiconductor Research Corporation(Grant number: 425.041)
Contact information:[email protected]://jhu.edu/crg/
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