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Capillary Electrophoresis 1. V+ V- 50 V/mm 2.3 UV-vis Spectrophotometer Detector
Citation preview
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