Capillary Electrophoresis of DNA-CNT

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Capillary Electrophoresis of DNA-CNT

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

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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?

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Capillary Electrophoresis
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UV-vis Spectrophotometer Detector
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CE Elution Profile
(575 nm)
Nanotube Stacking
Single Stranded DNA
B-DNA
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CE of CNT 575 nm, low concentration, no stacking
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What we learn from CE
Velocity v
Mobility U v / E
Slip plane

• Measure mobility
• Calculate zeta-potential
• Estimate charge density,
• Compare DNA with DNA-CNT
• Conclusions about DNA-CNT structure

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Mobility of DNA-CNT

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

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Zeta Potential of DNA-CNT

• Zeta potential found using Overbeeks expression1
  that neglects relaxation effect
• Relaxation effect then accounted for using
  Stigters results2

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 control
1 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).
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2 D. Stigter, The Journal of Physical Chemistry
82, 1417 (1978).
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Charge Density of DNA-CNT

• Debye-Huckel approximation used to estimate
  charge density
• Double Stranded DNA calculated to have 3.7-4.4
  e-/nm, compared to actual value of 5.88 e-/nm
• Double Stranded B DNA used as correction

DH theory Corrected
(6,5) DNA-CNT 3.6-4.5 e-/nm 5.8-6.0 e-/nm
(7,5) DNA-CNT 4.0-5.0 e-/nm 6.5-6.7 e-/nm
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Considering DNA-CNT structure
Ming Zheng et al., Nature Materials 2 (2003) 338
Presently Calculated Previously Postulated1
Charge Density of (6,5) DNA-CNT e-/nm 5.9 (6,5) 6.6 (7,5) 3.0 (for thicker CNTs, 2 strands, 18 nm pitch)
Mass DNA/ Mass CNT 1.3 for (6,5) 1.3 for (7,5) 1
Helical Pitch for 2 strands 3.7 nm 18 nm (from AFM images)
1Ming Zheng et al., Science 302(5650) 1545-8
(2003).
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Metellic vs Semiconducting CNT Mobility Comparison
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Mobility f(salt) part I
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Mobility f(salt) part II

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

Salt concentration (mM)
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EOF mobility f(salt)
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DNA-CNT sorting by CE I
Conversion of time axis to mobility
Mobility velocity / Electric field
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DNA-CNT Sorting by CE II
Comparing Absorbance Spectra of Different
Mobility Fractions
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