Modulation of Conductance in a Carbon Nanotube Field Effect Transistor by Electrochemical Gating - A pplication 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)

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 Buffer chamber CNT V sd Si/SiO 2 Filling port S D G Syringe Reservoir Au-wire Ag/AgCl Connecting port 17% KNO 3 5% KCl Choice of 3 gate electrodes

Diameter-dependent oxidation by K 2 IrCl 6 (Em K 2 IrCl 6 /K 3 IrCl 6 = 860 mV vs. NHE) Zheng and Diner (2004) JACS 126, DNA-dispersed HiPco single- walled carbon nanotubes easier to oxidize than nonionic dispersed nanotubes The larger the diameter the easier the nanotube is to oxidize CNT can be readily oxidized by strong oxidants such as K 2 IrCl 6, and fully reduced back by reductants such as Na 2 S 2 O mV vs NHE for (6,5)

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

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

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

Metallic CNT Semiconducting CNT CVD-grown nanotubes

Drain SiO 2 Si Source V sd VgVg CNT CNT-FET p-type (100) Si wafer Gate SiO 2 I sd vs.V g at different V sd Post-Burn, I sd vs.V g at different V sd Thinning as described by Ph. Avouris (2002) Chem. Phys. 281, 429 FF + Vg - Vg<0

Buffer chamber CNT V sd Si/SiO 2 Filling port S D G Syringe Reservoir Au-wire Ag/AgCl Connecting port 17% KNO 3 5% KCl Choice of 3 gate electrodes

Oxidation and reduction by ferri- and ferrocyanide of aqueous dispersions of CNTs oxidation reduction Em K 3 Fe(CN) 6 /K 4 Fe(CN) 6 = 361 mV 3 min and 8 min after the addition of 1 mM K 3 Fe(CN) 6 in 50 mM glycine pH 9.0.

K 3 Fe(CN) 6 and K 4 Fe(CN) 6 in reservoir only K 3 Fe(CN) 6 and K 4 Fe(CN) 6 throughout K 3 Fe(CN) 6 and K 4 Fe(CN) 6 in reservoir only Au wire gate in reservoir Ag/AgCl gate in reservoir K 3 Fe(CN) 6 and K 4 Fe(CN) 6 throughout CNT V sd Si/SiO 2 Vg Em K 3 Fe(CN) 6 /K 4 Fe(CN) 6 = 361 mV Gate electrodes Heller et al (2006) JACS 128,

Summary There are two ways in which swCNT-FETs respond to changes in the redox potential of solution: 1)Response of gold gate electrode to redox couple shifts the electrostatic potential of the solution. 2)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).

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.

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

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.

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)

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

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 Calculate Fermi level: close enough to last step? Calculate gate voltage Calculate the conductance Calculate the source-drain current Y N

Example

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

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

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

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

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

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 Buffer chamber CNT V sd Si/SiO 2 Filling port S D G Syringe Reservoir Au-wire Ag/AgCl Connecting port 17% KNO 3 5% KCl Choice of 3 gate electrodes

patterned chip sensing chamber (4.4 μl) o-ring inout Gate electrode (negative Vg) Liquid flow cell

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