1. Charge-Based Biosensor Using Carbon Nanotube Transistors Array Presenter: Jui-Ping Chiang

2. Outline Introduction of field effect detection of DNA hybridization Experiments –Fabrication –Hybridization –Measurements Results

3. Detection of hybridization Hybridization: combining complementary, single-stranded nucleic acids into a single molecule A single strand of DNA with 15 bases long has a charge of -15q (2.4 aC) Charges adsorbed on the electrolyte-insulator-silicon (EIS) structure produce a field effect to shift the flat band potential and/or change the capacitive/resistive impedance across the EIS structure 10q e 20q e DNA hyb. Sensor

4. In a very simplified model, the threshold voltage shift is given by Express the effective capacitance as: e.g. For 10mM TE buffer used during measurement, For DNA hybridization, we get positive threshold voltage shift

5. Fluorescent Pros: –Well-established –Very sensitive (sensitivity depends of sophistication of detection instrument) –3 zeptomolar (10 -21 M) has been reported Cons: –Instrument-heavy: photomultiplier, electronics –Labeled Other labeled methods: Electrochemical redox… Compared to fluorescent method... Field effect Pros: – Simple device structure, scalable – Probe attached to oxide: protocols are compatible – label-free – Sensitivity around nM range Cons: – Real-monitoring not possible, unless charge-less PNA probes are used Other labeled methods: surface plasmon resonance; ellipsometry; THz-transmission analysis; capacitance measurement; SAW devices…

6. Prepare iron catalyst: - Brief iron evaporation in UHV CNT growth in CVD furnace Cool down Most single walled, and contain both semiconducting and metallic type in roughly 2:1 proportion (metallic CNTs would be burned out later) exhaust ethylene hydrogen methane argon 850 ºC Device fabricaiton: carbon nanotube growth

7. Spin on photoresist, pre- bake at 90 ºC for 1 min Photoresist development Lift-off SD SiO 2 Al 2 O 3 Final structure: Carbon nanotube mats on silicon dioxide substrate silicon carbon nanotubes silicon dioxide UV exposure photoresist mask Metallization gold Device fabrication: microlithography Similar steps to mask active area during oxygen plasma etch

8. The active area between source and drain electrodes where the nanotube channel sits is 10um long and 50um wide. S D

9. DNA immobilization and hybridization 1.Aluminium oxide surface hydroxylation: O 2 plasma 2.Exposed to 3-mercapto-propyl-trimethoxy-silane (MPTMS) vapor 3.10 mM of Acrydite™-modified probe oligonucleotide dissolved in TE buffer (pH 7), was pipetted to the chip. Dry overnight 4.Measure the transfer characteristics (I DS -V GS curves) 5.Incubate the target DNA of on the chip up to 2 hrs in 100% humidity 6.Wash the whole chip throughly in TE buffer

10. Measurement Applied fixed 100 mV bias between the drain and source electrode. I DS was recorded as V GS was swept to generate transistor transfer characteristic curve.

11. The shift in threshold voltage, which arises from the additional surface charges, serves as the hybridization signal -0.500.511.5 8 10 12 14 16 18 20 22 24 26 V GS (V) I DS (  A) probe only 1uM hybridization dehybridization wash fluorescent image of 1uM complementary target hybridization fluorescent image after dehybridization wash to remove target DNA Results

12. Threshold voltage shift of all transistors are positive upon DNA hybridization, and the recovery upon target DNA denaturation are universal The amount of voltage shift should not depend on the initial position of the transistor’s threshold voltage 051015202530 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 device no. threshold voltage (V) probe only 1uM hybridization dehybridization wash

13. For different target DNA concentrations –Sensitivity: 10~100 nM –To be useful for diagnostic applications, the sensitivity of 1 pM or better is needed –Compelling estimates that suggest the feasilibity of achieving this level of detection through improved probe immobilization chemistry, better hybridization protocols and improved performance by using single CNT transistors The non-complementary signal serves as the noise floor

14. Thanks for your attention.