Hee Cheul ChoiDepartment of Chemistry,

Pohang University of Science and Technology (POSTECH)South Korea, 790-784

Carbon Nanotubes for Transistor Type-Biosensor and Therapeutic Applications

5th Korea-US NanoForum, Jeju, Korea, April 17-18, 2008

Surface Chemistry of Carbon nanotubes: Hybrid structures

Choi, et al., JACS 2002, 124, 9059.

Lee and Choi, et al., Small 2005, 1, 975.

Noble metal-SWNT composites

Transition metal-SWNT

Shin and Choi, et al., Adv. Mater. 2007, 19, 2873.

TiO2-SWNT composites

Facile and spontaneous synthetic approaches

Mechanism

Intercalation of Li ions in pyrene-functionalized SWNT

Modulation of band energy

Schottky diode behavior

Lithium intensity distribution (SPEM, Li 1s)

Lim and Choi, et al., JACS 2008, 130, 2160.

Surface Chemistry of Carbon nanotubes: Schottky diodes

O2

H2

CH4

C2H4SiO

CO

SiO2

Si

Byon and Choi, Nature Nanotech 2007, 2, 162.Byon and Choi, Nano Lett. 2008, 8, 178.

Carbothermal Reduction

Surface Chemistry of Carbon nanotubes: Carbothermal Reduction – Etching SiO2

Sub-10 nm scale Lithography using Nanotrenches

Byon and Choi, Nature Nanotech 2007, 2, 162.

Negative Differential Resistance (NDR) device- Ferritin captured in metallic SWNT nanogap electrodes

- Electrically cut m-SWNT (gap = ca. 20 nm)- Electrostatically captured Ferritins- Peak current density: 4.0 x 106 A cm-2 (record)- Peak-to-Valley Ratio (PVR): ~ 40 (@ scan rate of 26 mV/s)- NDR is 1.2 µohm cm2

Apoferrtin Apoferrtin + Fe(III)

Tang and Choi, et al., JACS 2007, 129, 11018.

Carbon nanotube electronics:Carbon nanotube/protein-based memory device

▪ Nonspecific Binding ▪ Specific Binding (using CDI-Tween20)

Robert J. Chen et al,. PNAS. 2003, 100, 4984

Electronic sensing of biomolecular recognitions using SWNTs-FETs

Sensitivity- At least ~ pM, grateful if it can go lower.- Protein detection limit of SWNT-FET: >10 nM(c.f. Lieber group: ~ 10 fM detection limit of proteins using SiNW

devices-Nat. Biotechol. 2005, 23, 1294.)

Feasibility- Prompt use: currently too long stabilization time- Nonspecific binding: perfect protection of devices with efficient

chemical blocking is mandatory.

Hurdles to overcome

Nanotube aspect: Direct charge communication between proteins and nanotubes

Metal-nanotube contact aspect: Schottky barrier modulation by protein adsorptions on metal surfaces

SiO2/Si

Au/Cr

Buffer Sol’n

Au/Cr

The two regions effecting to a biosensor sensitivity

Nanotube aspects: Charge injection from biomolecules Electric double layer field modulation caused by biomolecules

Metal-nanotube contact aspect:Adsorbed chemical species may modulate work function level of contactmetals, which consequently change the Schottky barrier height resulting in the conductance change.

Strongly depending on the pI (isoelectric point) values of proteins

+

Metal

Ener

gy

SemiconductingSWNT

VB

CB

Fermi level matching(EFM = EFS) &

Band bending of VB, CB

EFS

EFM

buffer

The origin of conductance changes: Schottky Barrier

Pd/Au evaporation

mPEG-SH SAM

SiO2/Si

PMMA

SWNT

s

SiO2/Si

SiO2/Si

s s sssssssss s

SiO2/Siss ss

Lift off

SiO2/Si

Lift off

Device I

S

OOMe

nS

OOMe

n

Device II

Chen, Choi, Dai et al, J. Am. Chem. Soc. 2004, 126, 1563

.50x10-6

1.48

1.46

1.44

I ds (µ

Α)

12008004000Time (s)

.50x10-6

3.45

3.40

3.35

3.30I d

s (µΑ

)

10008006004002000Time (s)

HIgG

Device I

Device II

100 nM

100 nM

Experimental evidence for the detection mechanism

SiO2/Si

▪ Synthesis of network SWNTs▪ Usage of the thin shadow mask▪ Thermal evaporator with tilted angle stages

Au/Cr Au/Cr

Increased Schottky contact area for high performance

V

10 mV

2000 μm

200 µm

Teflon electrochemical cell

Protein Injection

1 μM

CVD (900℃ 10 min)

SiO2/Si Substrate with Catalyst

CH4

H2

C2H4

Growth SWNTs

( R ~ 1 kΩ )

In wire

S D (Cu)

S DSiO2/Si

S D

Choi and Dai et al. Nano Lett. 2003, 3, 157.Yang and Choi et al. Langmuir 2005, 21, 9198.

Fabrication of SWNT-FET having increased Schottky contact area

(a) SWNT FET device fabricated by a photolithography

SWNTs Photo Resist

(1) Metal Evaporation (2) Lift Off

SiO2/Si

Au/Cr

(b) SWNT-FET device fabricated by a shadow mask at tilted angle

SWNTs Shadow Mask

angle evaporationSiO2/Si

Au/Cr

Byon and Choi. J. Am. Chem. Soc. 2006, 128, 2188.

Fabrication of SWNT-FET having increased Schottky contact area

▪ SA▪ SpA

Au/Cr

SiO2/Si

1 pM sensitivity

a SWNT-FET fabricated by a shadow mask at tilted angle

Buffer sol’n

Byon and Choi. J. Am. Chem. Soc. 2006, 128, 2188.

Highly sensitive SWNT-FET devices: Nonspecific bindings of proteins

1 pM sensitivity

a SWNT-FET fabricated by a shadow mask at tilted angle

a SWNT-FET fabricated by a shadow mask<Protein : SpA>

(unit : pM)

10 nM sensitivity

Highly sensitive SWNT-FET devices: Nonspecific bindings of proteins

Treatment of 0.05% Tween20 after immobilizing probe proteins

▪ Probe protein: Protein A▪ Target protein: rabbit IgG

▪ Probe protein: hCG▪ Target protein: anti β-hCG

1 pM sensitivity

Highly sensitive SWNT-FET devices: Specific bindings of proteins

Acknowledgement

CollaboratorsProf. Joon Won Park (POSTECH)Prof. Jillian M. Buriak (Univ. Alberta, Canada)Prof. Insung S. Choi (KAIST)Prof. Seunghun Hong (SNU)Prof. Jin Yong Lee (SKKU) Prof. Young Kyun Kwon (U. Mass)

Post DoctorsDr. Hyeon Suk ShinDr. Hye Ryung Byon

Graduate StudentsSeok Min YoonYoonmi LeeHyun Jae SongHyunseob LimHye Kyung MoonSuphil KimKyoung Ok KimJi Eun ParkKwangho Chu

UnderGraduate StudentsChee Bum Park

FundingsMOST, KOSEF, KRF, POSTECH

January 8, 2008