Modulation of Conductance in a Carbon Nanotube Field Effect Transistor by Electrochemical Gating

1. Modulation of Conductance in a Carbon Nanotube Field Effect Transistor by Electrochemical Gating - Application to the detection of unique sequences of DNA Bruce A. Diner#, Salah Boussaad#, T. Tang+, Anand Jagota* # DuPont CR&D * Lehigh University (Chemical Engineering) + University of Alberta (Mechanical Engineering) Co-workers: Xueping Jiang, Janine Fan and Kristin Ruebling-Jass (DuPont)

2. Ag/AgCl Au-wire 17% KNO3 5% KCl Reservoir Syringe Filling port Connecting port Choice of 3 gate electrodes chamber • Buffer G D S CNT Vsd Si/SiO2 Introduction CNT-FET in water with ions and redox species FET gated by electrode in solution Model for conductance DNA detection scheme (via activity of a redox enzyme) Outline

3. Diameter-dependent oxidation by K2IrCl6 (EmK2IrCl6/K3IrCl6= 860 mV vs. NHE) CNT can be readily oxidized by strong oxidants such as K2IrCl6, and fully reduced back by reductants such as Na2S2O4 The larger the diameter the easier the nanotube is to oxidize DNA-dispersed HiPco single-walled carbon nanotubes easier to oxidize than nonionic dispersed nanotubes 800 mV vs NHE for (6,5) Zheng and Diner (2004) JACS 126, 15490-15494

4. Electrolyte Gated CNT-FET’s High mobility, low contact-resistance High capacitance gating Gate voltage  NT potential Charge  Conductance Krüger et al. (2001) Appl. Phys Lett. 78, 1291 Rosenblatt et al. (2002) Nano Lett. 2, 869 J. Guo, M. Lundstrom and S. Datta, Appl. Phys., Lett. 80, 3192 (2002)

5. Addition of oxidizing molecules causes a +ve shift Addition of reducing molecules causes a –ve shift Electron transfer from CNT? Change in potential? Both? Larrimore et al. Nano Lett.6, 1329 (2006).

6. Chemical vapor deposition (CVD)-grown nanotubes AFM image courtesy of Scott Mclean Distances in µm 1 2 Catalyst pad 3 5 1 Devices made by Molecular Nanosystems Inc.

7. CVD-grown nanotubes Metallic CNT Semiconducting CNT

8. + Vg<0 Vg F - Isd vs.Vg at different Vsd Post-Burn,Isd vs.Vg at different Vsd CNT-FET Source Drain CNT Vsd SiO2 Si Gate SiO2 Vg p-type (100) Si wafer Thinning as described by Ph. Avouris (2002) Chem. Phys. 281, 429

9. Ag/AgCl Au-wire 17% KNO3 5% KCl Reservoir Syringe Filling port Connecting port Choice of 3 gate electrodes chamber • Buffer G D S CNT Vsd Si/SiO2

10. Oxidation and reduction by ferri- and ferrocyanide of aqueous dispersions of CNTs EmK3Fe(CN)6/K4Fe(CN)6 = 361 mV 3 min and 8 min after the addition of 1 mM K3Fe(CN)6 in 50 mM glycine pH 9.0. reduction oxidation

11. K3Fe(CN)6 and K4Fe(CN)6 in reservoir only K3Fe(CN)6 and K4Fe(CN)6 throughout • CNT Vsd Si/SiO2 Gate electrodes Vg Au wire gate in reservoir EmK3Fe(CN)6/K4Fe(CN)6 = 361 mV K3Fe(CN)6 and K4Fe(CN)6 in reservoir only K3Fe(CN)6 and K4Fe(CN)6 throughout Ag/AgCl gate in reservoir Ag/AgCl gate in reservoir Heller et al (2006) JACS 128, 7353-7359

12. Summary There are two ways in which swCNT-FETs respond to changes in the redox potential of solution: • Response of gold gate electrode to redox couple shifts the electrostatic potential of the solution. • At elevated redox potentials, the nanotubes themselves are oxidized by the oxidized member of the redox couple raising the concentration of p-type charge carriers (holes) which increases the nanotube conductance (Isd current).

13. Model for modulation of conductance Solution Electric potential controlled by the applied gate voltage. Induces an electric potential on the nanotube. (Need solution-CNT & quantum capacitance.) Potential on the nanotube shifts the band, induces carriers, changing conductance.

14. Interface of gate and solution: electrochemical equilibrium Gate voltage determines potential in solution through the Nernst equation Gate electrode area dominates Interfacial resistance dominates

15. Interface between solution and CNT: insulated For devices in water and for high salt concentrations , the electric potential experienced by the CNT is nearly identical to that in solution.

16. Charge generation on CNT J.W. Mintmire and C.T. White, Phys. Rev. Lett., 81, 2506 (1998) J. Guo, M. Lundstrom and S. Datta, Appl. Phys., Lett. 80, 3192 (2002) J. Guo, S. Goasguen, M. Lundstrom and S. Datta, Appl. Phys. Lett., 81, 1486 (2002)

17. G - Vg relation Purewal et al. PRL (2007; Kim group/Columbia) Rosenblatt et al. Nanoletters (2002)

18. Calculating Conductance Pick a potential on nanotube Given an initial guess for the Fermi level Calculate the charge induced on nanotube Calculate the potential in solution Calculate the electrochemical potential in solution N Calculate Fermi level: close enough to last step? Y Calculate the conductance Calculate gate voltage Calculate the source-drain current

19. Example

20. Shift Log([Ox]/[Red]) . Radius: 1 nm; Length Shift in Vg for one order of magnitude change in Debye length 2 nm. Larrimore et al. Nano Lett.6, 1329 (2006).

21. Effect of salt concentration Radius: 1 nm; Length Varying Debye length

22. Effect of NT diameter & length Length Radius 1nm Debye length 2 nm [Ox]/[Red] = 1 Debye length 2 nm [Ox]/[Red] = 1

23. ABTS-2 ABTS-1 Redox sensing using laccase bound by hybridization to surface coated with streptavidin biotinylated probe oligo attached to streptavidin S D Liquid Gate Laccase with attached oligo probe Time [Ox] Hybridized target oligo Time G 2,2’Azino-di-(3-ethylbenzthiazoline-sulfonate) (ABTS) D S Liquid Gate Em = 680 mV vs NHE

24. Isd at -0.1V gate voltage as a function of time with target at 100 amoles 100 amole complementary target ssDNA (Ol63) Facile detection of 100 attomoles target 100 amole non-complementary target ssDNA (Ol73)

25. Ag/AgCl Au-wire 17% KNO3 5% KCl Reservoir Syringe Filling port Connecting port Choice of 3 gate electrodes chamber • Buffer G D S CNT Vsd Si/SiO2 Introduction CNT-FET in water with ions and redox species FET gated by electrode in solution Model for conductance DNA detection scheme (via activity of a redox enzyme) Support: NASA, NSF. Summary

26. in out Liquid flow cell o-ring sensing chamber (4.4 μl) patterned chip Gate electrode (negative Vg)

27. Pads for source electrodes Pads for drain electrodes Zoom Pad for gate electrode 2nd generation CNT device custom made by Molecular Nanosystems Inc. Zoom 2 um 12 um 7 x 5 um Overcoated catalyst pads