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

2

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

6

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

7

Interaction of CNTs with Cell Membranes

Sylvia S. Mader, Biology, 9th ed., 2007, McGraw-Hill Companies, Inc.

8

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

9

Objective

To investigate the influence of solution chemistry on deposition and remobilization of MWNTs on model cell membranes

10

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

11

Preparation of MWNT Stock Suspensions

Sonication

Centrifugation

20 hours

5 mins,1400 RCF

Supernatant

12

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

13

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

14

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

15

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)

16

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)

23

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)

26

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

27

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

29

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

31

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

32

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:kailoon.chen@jhu.eduhttp://jhu.edu/crg/

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