research summary 20090111
DESCRIPTION
My Research in UW-MadisonTRANSCRIPT
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Research Summary* Chemoselective Nanowire Fuses: Chemically Induced Cleavage and Electrical Detection of Carbon Nanofiber Bridges
* Nanowire Fuses for Biological Detection: An Enzyme-Based Cleavage and Real-time Electrical Detection of Carbon Nanofiber Bridges
* Non-specific Adsorption of Nanowires to Surface: the Influence of Solution Compositon
* Photochemical grafting on TiO2 thin film
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• Ohmic contact is needed• Analog signal - Signal drift• Only effective in deionized water• Salt solution is necessary for
biomolecular interaction
Electrical Addressable Nanoscale Biosensors
Electrical detection: label-free, direct real-timeNanoscale biosensor: miniaturization, dense array, high sensitivity
Hahm, J., et al, Nano Letters, 2004(4), 51-54
•Measure conductance change
•Sensitive and specificity
•Tens of femtomolar DNA
•Single base specificity
Can we develop a biosensor working in salt solution?
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Research GoalsOur goals are (1) to develop a new form of inherently "digital" nanowire sensor based on making/breaking an electrical connection of a nanowire bridging between two electrodes, and (2) to understand how to manipulate and control nanoscale materials for novel sensing applications.
Challenges:1) Biomolecular recognition --> To develop biomolecular functionalization chemistry2) Choice of nanoscale materials --> To impact nonspecific binding, chemical stability3) Sensitivity--> Need to use high saline solutions, resulting in high background current
Cleavable Chemical/ Biological Group
nanowirenanowire
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Nanowire Fuses for Biological Detection
DNA and endonuclease are used to demonstrate the ability of biosensor fuse
Modified NWs
Amorphous Carbon Microelectrodes
Complementaryss-DNAs
AluI
I(f)
AG
CT T
CG
A
“0”“1”
AluI: restriction nuclease to cleave ds-DNA5'-A G^C T-3'3'-T C^G A-5'
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Synthesis and Functionalization of Carbon Nanofiber (CNF)
300nm
Carbon-based Materials as biological interface- Highly controllable surface chemistry- Excellent stability and biological activity
M. Endo et al., Appl. Phys. Lett. 2002, 80, 1267.
CarbonCarbon
H HHH
254 nm
HNF3C
OHN
F3CO
Carbon
H2N
NO
NO O
O
OO
SO3-
Carbon
HN
NO O
O
S
SH
SSMCC
DN
A
DN
A
NaBH4
MeOH
Yang, W. S., Hamers, R. J., et al., Nature Materials 2002, 1, 253.
Sun, B., Hamers, R. J., et al., LANGMUIR 2006, 22: 9598
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Manipulation of Nanofibers
~
Dielectrophoresis combined with fluid flow is used to assemble nanowire to form circuit
1 µm
Carbon nanofiber was manipulated under 0.2 Vpp at 1 MHz in deionized water
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PDMS cell
Quartz cover slip
Instrument Setup
Vmeas. = 20 mVrms at 20 kHz
FunctionGenerator
Meas. I/V converter
Lock-inAmplifier
10mM solution
Ref.
All-pass filter
“Internal Nulling” “External Nulling”
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Flow Flow
320
300
280
Cu
rren
t (p
A)
12080400
Time (s)
Current signal change (~21 pA) due to the nanowire unbridging are detected in 10 mM buffer.
Real-time Detection of Nanowire Unbridging
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Frequency-dependent Current Change
Change in current is directly proportional to frequency
3
4
6
8
10
2
Cu
rren
t ch
ang
e, p
A
3 4 6 8
104
2 4
Frequency, Hz
2
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Summary and Future Work
We have developed a new type of biological detection element that is based on the direct digital detection of the of binding/release of individual nanowires across electrodes in saline solutions. To achieve this requires, we need to understand how to optimize the biochemical, mechanical, and electrical properties of nanoscale materials in saline environments.
As a proof-of-concept, we have demonstrated the ability to combine these element to achieve direct real-time detection of enzymatic cleavage of double-stranded DNA molecules.
To summarize…
“0”
“1”
RNA Aptamer
target
I(f) ~
When RNA aptamer binds a specific target, the aptamer is cleaved, and the bio-switch is opened
Future work…
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Photochemical Grafting onto TiO2 Thin Film
•TiO2 exhibits high stability over a wide range of pH and has good
optical and electronic properties, making it of interest for applications in sensing and renewable energy.•TiO2 is of importance as a naturally forming surface coating on Ti and
Ti alloys, which are widely used in biomedical applications.
Motivation
Previous Methods for Surface Functionalization
• Silane• Carboxylic acid group• Phosphonic acid group
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Our Approach…
How does it work?
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FTIR & XPS Analysis of TiO2 after TFAAD Grafting and Deprotection
TiO2Si or glass
TFAADFused Silica Window
UV/254nm
2000 1600 1200
10
8
6
4
2
0Ab
sorb
ance
(10
-3)
3600 3200 2800Wavenumbers (cm-1)
deprotected
TFAAD/TiO2(a)
(b)
-CF3-C=O
TFAAD can be grafted to TiO2 surface and deprotected to form free amine terminated surface
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Are DNA on TiO2 surface stable?F2
Denaturate, then F1
S1 S2
Denaturate, then F1+F2
S1 S2
S1 S2
Inte
ns
ity
86420
Inte
nsi
ty
86420
Inte
nsi
ty
86420Distance (mm)
Day1
Day2
Day3
Day4
1.0
0.8
0.6
0.4
0.2
0.0
No
rmal
ized
Inte
nsi
ty
2520151050Cycle Number
TiO2
HN
N OO
O
S
TiO2
HN
N OO
O
S
Denatured in 8.3 M urea
DNAs tethered on TiO2 surface show excellent specificity and good stability
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Can We Photopattern TiO2 Surface?
50 μm
5 μm
240
200
160
120
Rel
ati
ve
inte
nsi
ty
250200150100500Distance (um)
TiO2
Si or glass
TFAADMask
Mask
SEM
TiO2
RR R RR
h
2 mm
NaBH4
65 ºC
NH
2
NH
2
NH
2
NH
2
NH
2
NH
2
TiO2
TiO2 TiO2
TiO2
SH
SS
MC
C
hF3C
HNO
TiO2 thin film can be photopatterned by TFAAD and then DNA molecules.
TiO2
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•Organic alkenes can graft to the surface of TiO2 when illuminated with ultraviolet light at 254 nm;
• The TFAAD-grafted surfaces can serve as a starting point for preparation of DNA-modified TiO2 thin films exhibiting excellent stability and selectivity;
• Chemical / biological molecules can be grafted to surface selectively;
• Our results suggest that the use of TiO2 as a thin transparent coating may provide enhanced control over the surface chemistry and yield (bio)molecular layers that are more reproducible and/or more stable than layers produced on glass and other transparent materials.
Summary
To summarize…