1. Capillary Electrophoresis of DNA-CNT Constantine Khripin, Dr. Ming Zheng, Prof. Anand Jagota

2. 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?

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

4. CE Elution Profile acetone Single Stranded DNA B-DNA Nanotube Stacking 4 (575 nm)

5. CE of CNT: 575 nm, low concentration, no stacking 5

6. What 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 6

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

8. Zeta Potential of DNA-CNT Zeta potential found using Overbeek’s expression 1 that neglects relaxation effectZeta potential found using Overbeek’s expression 1 that neglects relaxation effect –Relaxation effect then accounted for using Stigter’s results 2 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).} 2 D. Stigter, The Journal of Physical Chemistry 82, 1417 (1978). 8

9. Charge Density of DNA-CNT Debye-Huckel approximation used to estimate charge densityDebye-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 - /nmDouble 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 correctionDouble 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 9

10. Considering DNA-CNT structure Presently Calculated Previously Postulated 1 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) Ming Zheng et al., Nature Materials 2 (2003) 338 10 1 Ming Zheng et al., Science 302(5650) 1545-8 (2003).

11. Metellic vs Semiconducting CNT Mobility Comparison

12. Mobility f(salt) part I

13. Mobility f(salt) part II Error bars are standard deviation of elution peak Peaks are much broader at lower salt concentrations Salt concentration (mM)

14. EOF mobility f(salt)

15. DNA-CNT sorting by CE I: Conversion of time axis to mobility Mobility = velocity / E lectric field 15

16. DNA-CNT Sorting by CE II: Comparing Absorbance Spectra of Different Mobility Fractions 16