Toshihito Ohtake

Nanoimprint and lift-off process using poly vinyl alcohol

We developed a lift-off process for a nanoimprint lithography (NIL) using poly(vinyl alcohol) (PVA) as the replicated material. PVA could easily be dissolved in water. A conventional lift-off process using poly(metyl methacrylate) (PMMA) uses acetone as a solvent, while the lift-off process using PVA uses water as a solvent, which is an ecologically friendly process. We demonstrated Au patterns with sub-µm dimensions using a lift-off process with a PVA single layer. In addition, an Hydrogen silsesquioxane (HSQ)/PVA bilayer structure was used for the lift-off process. This bilayer structure could be fabricated by room-temperature NIL and dry etching. Au patterns were easily obtained using the bilayer structure having an inverse tapered shape. In the lift-off process without using HSQ/PVA bilayer, Au wiring with sub-µm linewidth could be obtained, however, 100-nm-linewidth patterns did not remained. Line-and-spacing gratings of 100 nm in the Au patterns were demonstrated using the water lift-off process with the HSQ/PVA bilayer structure.

DNA nanopatterning with self-organization by using nanoimprint

Recently, DNA properties have been investigated to realize new functional biodevices. However, there are few reports on DNA nanopatterning to make bionanodevices. Therefore, we have attempted DNA nanopatterning by using a nanoimprint method. On a glass substrate coated with poly-L-lysine, which is known as a material for DNA immobilization by UV radiation, about 100 μl of a 1μg∕μl DNA solution was applied and was dried at 60 °C for an hour, and was irradiated by UV for 2 min. Further 4% polyvinyl alcohol (PVA) solution was coated on the substrate. The substrate was imprinted at 100 °C and 6 MPa for 5 min, and a mold was applied with a SiO2 on Si substrate fabricated by electron-beam lithography and dry etching. Etching of the DNA substrate was done by reactive ion etching in O2 atmosphere. Finally, the PVA layer washed down by water, and the DNA nanopatterning was obtained.

Direct Deoxyribonucleic Acid Detection Using Ion-Sensitive Field-Effect Transistors Based on Peptide Nucleic Acid

We have investigated an ion-sensitive field-effect transistor (IS-FET)-based biosensor to directly monitor the hybridization of deoxyribonucleic acid (DNA) using peptide nucleic acid (PNA) as a probe. The PNA was immobilized on a Ta2O5 gate surface using aminosilane via glutaraldehyde as a bifunctional crosslinker. Variations in surface charge density in the gate region of the IS-FET were monitored as shifts in threshold voltage after DNA hybridization. Large positive shifts in threshold voltage, as high as 170 mV, were observed during ID-VG measurements. The changes in threshold voltage observed for neutral PNA-immobilized IS-FETs were more than 5 times greater than those for negatively charged DNA-immobilized IS-FETs. Thus, this approach demonstrates that the PNA-modified IS-FET-based biosensor works more effectively as a signal transducer of genetic information. We expect potential applications in medical diagnostics and molecular biology.

Immobilization of probe DNA on Ta2O5 thin film and detection of hybridized helix DNA using IS-FET

We demonstrated developments of a non-labeling DNA (deoxyribonucleic acid) sensor by using a commercially available ion-sensitive field-effect transistor (IS-FET). A single strand DNA was immobilized on a Ta2O5 thin film on a gate electrode in the IS-FET, and the surface of the thin film was confirmed by XPS measurements. The results indicated that the DNA was immobilized on the Ta2O5 thin film. To detect the hybridization of DNA, we carried out measurements of Idrain-Vgs properties of IS-FETs immobilized by ss-DNA and ds-DNA hybridized by complemental target DNA. Then, the difference in threshold voltage was evaluated to be about 10 mV, and the amount of immobilized DNA as 6.3×107 [molecules/cm2]. Consequently, the non-labeling IS-FET DNA sensor is expected to be a novel measurement tool for diagnosing diseases.

Direct DNA detection using ion-sensitive field effect transistors (IS-FETs) based on peptide nucleic acid

Molecular recognition based on DNA hybridization is an important reaction in biotechnology. Bio-devices that are able to discriminate between double-stranded nucleic acids and single stranded nucleic acids with high efficiency and specificity are useful tools in this post-genome sequence era. In this study, we focused on a direct detection system for DNA hybridization that combines device function with efficient molecular recognition of heterogeneous nucleic acid hybridization.