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