My Research in UW-Madison

1. 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

3. 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

6. 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

7. Instrument Setup V meas. = 20 mV rms at 20 kHz Function Generator Meas.  I/V converter Lock-in Amplifier 10mM solution Ref. All-pass filter “ Internal Nulling” “ External Nulling” PDMS cell Quartz cover slip

8. 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)

9. 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

10. 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”

12. Our Approach… How does it work?

13. 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

14. 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

15. 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