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 TiO 2 thin film
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-time Nanoscale biosensor: miniaturization, dense array, high sensitivity
Measure conductance change
Sensitive and specificity
Tens of femtomolar DNA
Single base specificity
Can we develop a biosensor working in salt solution? Hahm, J., et al, Nano Letters, 2004(4), 51-54
Research Goals Our 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 chemistry 2) Choice of nanoscale materials --> To impact nonspecific binding, chemical stability 3) Sensitivity--> Need to use high saline solutions, resulting in high background current Cleavable Chemical/ Biological Group nanowire nanowire
Nanowire Fuses for Biological Detection DNA and endonuclease are used to demonstrate the ability of biosensor fuse Modified NWs Amorphous Carbon Microelectrodes Complementary ss-DNAs AluI I(f) AGCT TCGA
AluI: restriction nuclease to cleave ds-DNA
5'-A G^C T-3'
3'-T C^G A-5'
“ 0” “ 1”
Synthesis and Functionalization of Carbon Nanofiber (CNF)
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. Yang, W. S., Hamers, R. J., et al., Nature Materials 2002 , 1, 253. Sun, B., Hamers, R. J., et al., LANGMUIR 2006 , 22: 9598 300nm Carbon Carbon H H H H 254 nm Carbon Carbon SH SSMCC DNA DNA NaBH 4 MeOH
Manipulation of Nanofibers Dielectrophoresis combined with fluid flow is used to assemble nanowire to form circuit Carbon nanofiber was manipulated under 0.2 Vpp at 1 MHz in deionized water ~ 1 µm
Flow Flow Current signal change (~21 pA) due to the nanowire unbridging are detected in 10 mM buffer. Real-time Detection of Nanowire Unbridging 320 300 280 Current (pA) 120 80 40 0 Time (s)
Frequency-dependent Current Change Change in current is directly proportional to frequency 3 4 6 8 10 2 Current change, pA 3 4 6 8 10 4 2 4 Frequency, Hz 2
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… RNA Aptamer target I(f) ~ When RNA aptamer binds a specific target, the aptamer is cleaved, and the bio-switch is opened Future work… “ 0” “ 1”
Photochemical Grafting onto TiO 2 Thin Film
TiO 2 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.
TiO 2 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
Carboxylic acid group
Phosphonic acid group
Our Approach… How does it work?
FTIR & XPS Analysis of TiO 2 after TFAAD Grafting and Deprotection TiO 2 Si or glass TFAAD Fused Silica Window UV/254nm TFAAD can be grafted to TiO 2 surface and deprotected to form free amine terminated surface 2000 1600 1200 10 8 6 4 2 0 Absorbance (10 -3 ) 3600 3200 2800 Wavenumbers (cm -1 ) deprotected TFAAD/TiO 2 (a) (b) -CF 3 -C=O
Are DNA on TiO 2 surface stable? F2 Denaturate, then F1 S1 S2 Denaturate, then F1+F2 S1 S2 S1 S2 Intensity 8 6 4 2 0 Intensity 8 6 4 2 0 Distance (mm) Denatured in 8.3 M urea DNAs tethered on TiO 2 surface show excellent specificity and good stability Intensity 8 6 4 2 0 Day 1 Day 2 Day 3 Day 4 1.0 0.8 0.6 0.4 0.2 0.0 Normalized Intensity 25 20 15 10 5 0 Cycle Number TiO 2 H N N O O O S TiO 2 H N N O O O S
Can We Photopattern TiO 2 Surface? 50 μ m 5 μ m TiO 2 Si or glass TFAAD Mask Mask SEM R R R R h 2 mm NaBH 4 65 ºC NH 2 NH 2 NH 2 NH 2 NH 2 NH 2 TiO 2 TiO 2 TiO 2 TiO 2 SH SSMCC h F 3 C H N O TiO 2 thin film can be photopatterned by TFAAD and then DNA molecules. TiO 2 240 200 160 120 Relative intensity 250 200 150 100 50 0 Distance (um) TiO 2 R
Organic alkenes can graft to the surface of TiO 2 when illuminated with ultraviolet light at 254 nm;
The TFAAD-grafted surfaces can serve as a starting point for preparation of DNA-modified TiO 2 thin films exhibiting excellent stability and selectivity;
Chemical / biological molecules can be grafted to surface selectively;
Our results suggest that the use of TiO 2 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.