Capillary Electrophoresis of DNA-CNT

Constantine Khripin, Dr. Ming Zheng, Prof. Anand Jagota

Outline

• Structure evaluation of DNA-CNT by CE– We determine electrophoretic mobility from

CE and use that to calculate charge density of DNA-CNT

• Sorting of DNA-CNT by CE– Is CE a useful tool for sorting DNA-CNT?

Capillary ElectrophoresisCapillary Electrophoresis1.

V+V-

50 V/mm

2.

33

UV-vis Spectrophotometer Detector

CE Elution ProfileCE Elution Profile

0 5 10 15 20 25Time (min)

Abso

rban

ce (a

rbitr

ary

units

) DNA-CNT (260 nm)DNA (260 nm)

acetone

Single Stranded DNA

B-DNA

Nanotube Stacking

44

(575 nm)

CE of CNT: 575 nm, low CE of CNT: 575 nm, low concentration, no stackingconcentration, no stacking

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0 5 10 15 20 25

Time (min)

Abs

orba

nce

(mA

)

55

What we learn from CEWhat we learn from CE

Velocity v

Mobility U = v / E • Measure mobility• Calculate zeta-potential• Estimate charge density, • Compare DNA with DNA-CNT• Conclusions about DNA-CNT structure

Slip plane

66

Mobility of DNA-CNTMobility of DNA-CNT

77

Mobilities:

• DNA-CNT > ssDNA• DNA-CNT >~ dsDNA• Independent of length• Independent of concentration• No difference between (6,5), (7,5)

Zeta Potential of DNA-CNTZeta Potential of DNA-CNT• Zeta potential found using Overbeek’s expressionZeta potential found using Overbeek’s expression11 that neglects that neglects

relaxation effectrelaxation effect

– Relaxation effect then accounted for using Stigter’s resultsRelaxation effect then accounted for using Stigter’s results22

o

II uuu32

32

31

Double-stranded DNA has very similar zeta potential to DNA-CNT, similar diameter (2.2 nm for DNA vs. 2.1 for (6,5) DNA-CNT); thus B-DNA is a good control1 J. Th. G. Overbeek and B. H. Bijsterbosch, “The Electrical Double Layer and the

Theory of Electrophoresis” {in P. G. Righetti, van Oss, C.J., J. W., Electrokinetic Separation Methods. (Elsevier, Amsterdam, 1979).}

2 D. Stigter, The Journal of Physical Chemistry 82, 1417 (1978). 88

Charge Density of DNA-CNTCharge Density of DNA-CNT• Debye-Huckel approximation used to estimate charge Debye-Huckel approximation used to estimate charge

densitydensity

• Double Stranded DNA calculated to have Double Stranded DNA calculated to have 3.7-4.4 3.7-4.4 ee--/nm,/nm, compared to actual value ofcompared to actual value of 5.88 5.88 ee--/nm/nm

• Double Stranded B DNA used as correctionDouble Stranded B DNA used as correction

akKakK

ako

oDH)(

2 1

DH theoryDH theory CorrectedCorrected

(6,5) DNA-CNT(6,5) DNA-CNT 3.6-4.5 e3.6-4.5 e--/nm/nm 5.8-6.0 e5.8-6.0 e--/nm/nm

(7,5) DNA-CNT(7,5) DNA-CNT 4.0-5.0 e4.0-5.0 e--/nm/nm 6.5-6.7 e6.5-6.7 e--/nm/nm99

Considering DNA-CNT structureConsidering DNA-CNT structurePresently Presently CalculatedCalculated

Previously Previously PostulatedPostulated11

Charge Charge Density of Density of (6,5) DNA-(6,5) DNA-CNTCNTee--/nm/nm

5.9 (6,5)5.9 (6,5)6.6 (7,5)6.6 (7,5)

3.0 (for 3.0 (for thicker thicker CNTs, 2 CNTs, 2 strands, 18 strands, 18 nm pitch)nm pitch)

Mass DNA/Mass DNA/Mass CNTMass CNT

1.3 for (6,5)1.3 for (6,5)1.3 for (7,5)1.3 for (7,5)

~1~1

Helical Pitch Helical Pitch for 2 strandsfor 2 strands

3.7 nm3.7 nm 18 nm (from 18 nm (from AFM AFM images)images)

Ming Zheng et al., Nature Materials 2 (2003) 338

1010

1Ming Zheng et al., Science 302(5650) 1545-8 (2003).

Metellic vs Semiconducting CNT Mobility Comparison

4.00

4.05

4.10

4.15

4.20

4.25

4.30

4.35

4.40

4.45

4.50

Laser S-C Nanotubes

Laser Metallic Nanotubes

DS DNA

Mob

ility

u (c

m2 /V

s * 1

04 )

Mobility f(salt) part I

3

3.5

4

4.5

5

5.5

6

0.10 1.00 10.00 100.00

SS DNA

DS DNA

(6,5) 30 V

(6,5) 15 V

Mob

ility

u (c

m2 /V

s * 1

04 )

Mobility f(salt) part II

•Error bars are standard deviation of elution peak•Peaks are much broader at lower salt concentrations

3

3.5

4

4.5

5

5.5

6

6.5

0.1 1.0 10.0 100.0

Salt concentration (mM)

Mob

ility

u (c

m2 /V

s * 1

04 )

EOF mobility f(salt)

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

0.1 1 10 100salt (mM)

EOF

mob

ility

SS DNA

function fit

(6,5) 15 V

(6,5) 30 kV

DS DNA

DNA-CNT sorting by CE I:DNA-CNT sorting by CE I:Conversion of time axis to mobility

Mobility = velocity / Electric field

1515

DNA-CNT Sorting by CE II:DNA-CNT Sorting by CE II:Comparing Absorbance Spectra of Different Mobility Fractions

1616