Yasuyuki Tsuboi

Permanent fixing or reversible trapping and release of DNA micropatterns on a gold nanostructure using continuous-wave or femtosecond-pulsed near-infrared laser light.

The use of localized surface plasmons (LSPs) for highly sensitive biosensors has already been investigated, and they are currently being applied for the optical manipulation of small nanoparticles. The objective of this work was the optical trapping of λ-DNA on a metallic nanostructure with femtosecond-pulsed (fs) laser irradiation. Continuous-wave laser irradiation, which is generally used for plasmon excitation, not only increased the electromagnetic field intensity but also generated heat around the nanostructure, causing the DNA to become permanently fixed on the plasmonic substrate. Using fs laser irradiation, on the other hand, the reversible trapping and release of the DNA was achieved by switching the fs laser irradiation on and off. This trap-and-release behavior was clearly observed using a fluorescence microscope. This technique can also be used to manipulate other biomolecules such as nucleic acids, proteins, and polysaccharides and will prove to be a useful tool in the fabrication of biosensors.

Pulsed laser deposition of collagen and keratin

Pulsed laser deposition of collagen and keratin, which are representative fibrous proteins, were investigated in terms of laser wavelength and fluence. Chemical structure and surface morphology of thin deposited films were analyzed by means of infrared (IR) spectroscopy and atomic force microscopy (AFM), respectively. For the couple of proteins, IR spectra of the films deposited under some irradiation conditions were almost similar to those of starting targets. This means that a large part of primary structure of the proteins was maintained in the thin deposited films. Also the secondary structures in the thin films were discussed briefly. The random-coil domains increased both for collagen and keratin. Thus we have demonstrated that laser lights are capable of preparing thin films of proteins.

Pulsed laser deposition of silk protein: Effect of photosensitized-ablation on the secondary structure in thin deposited films

Silk fibroin is a simple protein expected to have functional applications in medicine and bioelectronics. The primary structure of this protein is quite simple, and the main secondary structures are β-sheet crystals and amorphous random coils. In the present study, we investigated pulsed laser deposition (PLD) of fibroin with the β-sheet structures as targets. The primary and secondary structures in films deposited were analyzed using infrared spectroscopy. Normal laser deposition at 351 nm using neat fibroin targets produced thin films of fibroin with a random coiled structure. Ablation was triggered by two-photonic excitation of the peptide chains, which resulted in the destruction of β-sheet structure in PLD. In order to avoid the two-photonic excitation, we adopted a PLD method utilizing anthracene (5–0.1 wt %) in a photosensitized reaction involving doped fibroin targets. Laser light (351 or 355 nm) was absorbed only by anthracene, which plays an important role converting photon energy to thermal ene...

Thin films formation of poly(N-vinylcarbazole) by laser ablation deposition

The laser-ablation deposition technique was examined for poly(N-vinylcarbazole), PVCz, which is a representative photoconductive aromatic vinylpolymer. Thin films were deposited under various irradiation conditions (laser wavelengths were 351, 308, and 248 nm and their fluences were 70, 300, and 450 mJ/cm2), and their chemical structures and surface morphology were revealed by means of infrared-absorption, fluorescence spectroscopy, and atomic force microscopy, respectively. They were quite sensitive to the laser fluence, as well as wavelength. A thin film of PVCz was formed only under an optimum irradiation condition where the laser fluence and wavelength were 300 mJ/cm2 and 351 nm, respectively. When the irradiation condition deviated from the optimum one, thin films contained carbazolyl derivatives such as N-alkylcarbazole and N-vinylcarbazole oligomers. It was revealed that the thin PVCz film was formed by a repolymerization due to radical mechanism. In addition, it was suggested that cross-linking re...

Deposition of a thin polystyrene film by anthracene-photosensitized laser ablation at 351 nm

Pulsed laser deposition of polystyrene (PSt) was investigated using infrared and UV absorption spectroscopy. The essential of the present study is to use a PSt target doped with anthracene which plays an important role as a photosensitizer to induce ablation. Four types of deposition were examined by changing laser wavelength (248 and 351 nm) and ablation target (neat and doped PSt). For both of the targets, 248 nm ablation deposited no film, while 351 nm deposition gave thin films. In the latter, only when 351 nm laser light and the doped target were employed, a thin PSt film was deposited.

Photothermal Ablation of Polystyrene Film by 248 NM Excimer Laser Irradiation:a Mechanistic Study by Time-Resolved Measurements

Laser ablation mechanism at 248 nm irradiation of polystyrene film was investigated and discussed. An ablation threshold was determined by etch depth measurement and nanosecond photographic observation. Temperature at the threshold was evaluated to be 370℃ by using an effective absorption coefficient which was confirmed by transmission measurement of the excitation pulse. The temperature was in good agreement with that of thermal degradation of the polymer, showing that 248 nm ablation of polystyrene was brought about by a photothermal process. Nanosecond photography upon the ablation could be well interpreted from the photothermal viewpoint. Moreover, dynamics of excited species revealed by nanosecond time-resolved luminescence measurements was inferred in relation to the ablation.

Vacuum-deposited films of mesogen of 4-n-pentyl-4-cyano-p-terphenyl : their electronic spectra and molecular aggregate structures

Abstract Absorption and fluorescence spectra of 4-n-pentyl-4″-cyano-p-terphenyl (5CT) films deposited on hydrophilic and hydrophobic quartz substrates were measured and compared with those of its various solutions and of its neat forms (crystalline, liquid crystal, and isotropic phases). Further, these spectra were compared with those of 4-n-alkoxy-4′-cyanobiphenyls (nOCB, n=8, 9, 10, 12), which had been studied in detail already. The absorption and fluorescence spectra of the 5CT-deposited films were almost independent of substrate property and deposition temperature. This behavior was different from those observed for nOCB. The absorption spectra differed from those of its solution samples and suggested that cyanoterphenyl groups of 5CT molecules in the deposited films form H-aggregate-like structures with their long axes parallel to each other and relatively perpendicular to the stacking direction in the deposited films. The fluorescence spectra were also different from those of its neat and solution samples. Surface morphology of the deposited films was also investigated using atomic force microscopy (AFM). AFM images showed that the deposited films consisted of a number of small plate crystals, which was consistent with H-aggregate-like structures of cyanoterphenyl groups, and that the small plate crystals transformed to needle ones with time. The structural transformation correlated with the absorption and fluorescence spectral changes with time. The deposition processes of 5CT as revealed by in situ fluorescence spectra during deposition were simple compared with those of nOCB and are discussed on the basis of the in situ fluorescence spectra and the AFM images.

Magnetic Field Effect on Laser Ablation of Organic Polymer Films as Revealed by Atomic Force Microscopy

A magnetic field effects on 308 nm excimer laser ablation of poly(N-vinylcarbazole) (PVCz) films was investigated by means of atomic force microscopy. The morphology of ablated surface exhibited characteristic modification by applying a magnetic field. An orientation pattern was observed on the polymer surface ablated in a horizontal magnetic field. PVCz films prepared by the cast-method in a magnetic filed were not oriented. A novel technique combining laser light and a magnetic field was developed for sub-micron surface patterning.