論文 - 寺川　光洋

Synthesis of silicon carbide nanocrystals and multilayer graphitic carbon by femtosecond laser irradiation of polydimethylsiloxane

Hayashi S., Morosawa F., Terakawa M.

Nanoscale Advances （Nanoscale Advances）  2 （ 5 ） 1886 - 1893 2020年03月

研究論文（学術雑誌）, 共著, 査読有り

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© The Royal Society of Chemistry 2020. Laser-based modification of polymer materials has been emerging as a versatile and efficient technique to simultaneously form and pattern electrically conductive materials. Recently, it has been revealed that native polydimethylsiloxane (PDMS) can be modified into electrically conductive structures using femtosecond laser irradiation; however, the details regarding the structures formed by this method have yet to be revealed. In this work, structures were fabricated by focusing and scanning femtosecond laser pulses onto the surface of PDMS. Raman Spectroscopy and Transmission Electron Microscopy (TEM) analyses revealed the formation of silicon carbide (SiC) nanocrystals, as well as multilayer graphitic carbon, in the modified regions of PDMS. The state of the formed material differed depending on the distance from the focal spot, suggesting that photo-thermal effects contributed to the degradation of PDMS into conductive material. Electrical conductivity measurements, in addition to Raman results, indicated that the amount of disorder in the formed graphitic carbon contributes to the electrical conductivity of the fabricated structures.

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Effect of Pd-decoration on the sensing properties of ZnO nanostructures

Dilova T., Atanasova G., Og. Dikovska A., Avdeev G., Machida M., Terakawa M., Stefanov P., Nedyalkov N.

Thin Solid Films （Thin Solid Films）  693   137693 2020年01月

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© 2019 Elsevier B.V. In this work, we present fabrication and studies of pure and Pd-decorated ZnO nanostructures on Ag-coated substrates in view of gas-sensing application. The sensor elements consist of a dense structure of ZnO nanobelts. The chemical composition of the surface and gas-sensing properties of pure and Pd-doped nanostructures were studied and compared. On the surface of the Pd-decorated ZnO samples, the presence was found of Pd and Pd-Ag clusters, as well as isolated Pd2+ ions were incorporated into the ZnO lattice. The Pd-ZnO sensor element showed a better response to CO, NH3, and acetone compared to the pure ZnO sample. The Pd-ZnO sample exhibited its highest response to exposure to acetone at room temperature. We associate the improvement of sensing performance of the Pd-decorated ZnO nanostructures with the increased number of adsorption centers on the surface due to the Pd nanoparticles.

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Luminescence properties of laser-induced silver clusters in borosilicate glass

Nedyalkov N., Dikovska A., Koleva M., Stankova N., Nikov R., Borisova E., Genova T., Aleksandrov L., Iordanova R., Terakawa M.

Optical Materials （Optical Materials）  100 2019年12月

研究論文（学術雑誌）, 共著, 査読有り

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© 2019 Elsevier B.V. This paper describes the luminescence properties of small silver clusters formed by laser treatment of silver-doped borosilicate glass. Using irradiation by a Nd:YAG nanosecond laser system operating at the fourth harmonic wavelength (266 nm), areas are formed in the glass samples that emit bright luminescence peaking at about 600 nm when excited by UV light in the spectral range 300–390 nm. The influence is presented and discussed of the glass composition and the laser processing parameters on the emission characteristics. It is further shown that the luminescent properties are affected by the fluence of the excitation source, namely, a complete quenching of the emission is achieved above a certain value. The luminescence of the irradiated areas is explained by the formation of Ag clusters due to irradiation-induced reduction of Ag ions and increased atom mobility resulting from the local heating. The limited stability of the luminescent areas upon UV radiation can be related to heat-induced cluster decomposition and re-oxidation. The results obtained provide a new insight in the optical properties of noble-metal nanostructures and could form the basis of fabrication of complex optical systems and luminescent component used in the study of, e.g., biological systems.

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Fabrication of a monolithic lab-on-a-chip platform with integrated hydrogel waveguides for chemical sensing

Torres-Mapa M., Singh M., Simon O., Mapa J., Machida M., Günther A., Roth B., Heinemann D., Terakawa M., Heisterkamp A.

Sensors (Switzerland) （Sensors (Switzerland)）  19 （ 19 ）  2019年10月

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© 2019 by the authors. Licensee MDPI, Basel, Switzerland. Hydrogel waveguides have found increased use for variety of applications where biocompatibility and flexibility are important. In this work, we demonstrate the use of polyethylene glycol diacrylate (PEGDA) waveguides to realize a monolithic lab-on-a-chip device. We performed a comprehensive study on the swelling and optical properties for different chain lengths and concentrations in order to realize an integrated biocompatible waveguide in a microfluidic device for chemical sensing. Waveguiding properties of PEGDA hydrogel were used to guide excitation light into a microfluidic channel to measure the fluorescence emission profile of rhodamine 6G as well as collect the fluorescence signal from the same device. Overall, this work shows the potential of hydrogel waveguides to facilitate delivery and collection of optical signals for potential use in wearable and implantable lab-on-a-chip devices.

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Fabrication of metal microstructures in elastic hydrogel by multiphoton photoreduction

Terakawa M., Machida M., Onoe H., Niidome T., Heisterkamp A.

2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019 （2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019）  Part F140-CLEO_Europe 2019 2019年06月

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© 2019 IEEE. Soft materials, including elastic polymers and hydrogels, are promising materials for soft robots, implantable devices, and wearable devices owing to their flexibility and biocompatibility. In recent years, the scope of use of such soft materials is expanding further because of their integration with metal micro- and nanostructures, which exhibit attractive optical and electrical properties. In this study, we demonstrate the formation of metal microstructures inside a hydrogel by photoreduction of metal ion by using femtosecond laser. Because the hydrogels have permeability to fluids, metal ions are able to be added by simply immersing the hydrogel into the metal ion solution. Femtosecond laser pulses were focused and scanned in the hydrogel to fabricate metal microstructures [1, 2]. The optical diffraction pattern obtained with the silver grating inside the hydrogel showed spaced diffraction spots, which indicated that a regular, periodic silver grating was formed. Notably, the distance between the diffraction spots changed when the water content in the hydrogel was reduced. The grating period decreased when the hydrogel shrank owing to the loss of water (Fig. 1(a)), but the straight shapes of the line structures were preserved, which demonstrated the optical tunability of the fabricated structure.

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Strain sensing using electrically conductive structures fabricated by femtosecond-laser-based modification of PDMS

Hayashi S., Nakajima Y., Terakawa M.

Optical Materials Express （Optical Materials Express）  9 （ 6 ） 2672 - 2680 2019年05月

研究論文（学術雑誌）, 共著, 査読有り

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© 2019 Optical Society of America. Strain sensing was demonstrated by utilizing electrically conductive silicon-carbide (β-SiC) fabricated by femtosecond-laser-based direct modification of polydimethylsiloxane (PDMS). Depending on the laser scanning direction used for the fabrication procedure, the fabricated structures showed different sensitivity to strain and this difference was discussed by observing the surface morphology at various bending radii using scanning electron microscopy (SEM). The change in electrical conductance at the flat state after repeated bending was also investigated. Furthermore, preliminary demonstration of human motion sensing was performed using the fabricated structures. The presented method will open doors to novel electronic device applications using PDMS.

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Spatially-targeted laser fabrication of multi-metal microstructures inside a hydrogel

Machida M., Niidome T., Onoe H., Heisterkamp A., Terakawa M.

Optics Express （Optics Express）  27 （ 10 ） 14657 - 14666 2019年05月

研究論文（学術雑誌）, 共著, 査読有り

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© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement The spatially-targeted fabrication of bimetallic microstructures coexisting in the supporting hydrogel is demonstrated by multi-photon photoreduction. Microstructures composed of gold and silver were fabricated along a predefined trajectory by taking advantages of the hydrogel's ionic permeability. Different resonant wavelengths of optical absorption were obtained for gold, silver, and their bimetallic structures. Transmission electron microscopy and energy dispersive X-ray analysis revealed that the optical properties are attributable to the formation of bimetallic structure consisted of core-shell nanoparticles. The fabrication of dissimilar metal structures within hydrogel is a promising technique for optically driven actuators in soft robotics and sensing applications by allowing for site-selective optical properties.

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Photoacoustic diagnosis of pharmacokinetics and vascular shutdown effects in photodynamic treatment with indocyanine green-lactosome for a subcutaneous tumor in mice

Tsunoi Y., Araki K., Ozeki E., Hara I., Shiotani A., Terakawa M., Sato S.

Photodiagnosis and Photodynamic Therapy （Photodiagnosis and Photodynamic Therapy）  26   436 - 441 2019年05月

研究論文（学術雑誌）, 共著, 査読有り

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© 2019 Indocyanine green lactosome (ICG-lactosome) is an attractive new-generation agent for photodynamic therapy (PDT) that is characterized by a near-infrared excitation wavelength and high stability in the bloodstream. Fluorescence imaging has been used to examine its pharmacokinetics in vivo, but no depth-resolved information can be obtained with this method. In this study, we applied photoacoustic (PA) imaging to visualize the depth distribution of ICG-lactosome in a mouse subcutaneous tumor model. With this method, the depth distribution of blood vessels can also be visualized, enabling detection of vascular shutdown effects due to PDT. We performed PA imaging of both the distributions of ICG-lactosome and blood vessels in a tumor before and after PDT, and we found that PA signals originating from ICG-lactosome were greatly increased at 18 h after drug injection but rapidly decreased after PDT. These results indicate efficient accumulation of ICG-lactosome and rapid photobleaching due to the PDT reaction in the tumor, respectively. After PDT, PA amplitudes of hemoglobin were significantly decreased, being attributable to vascular shutdown effects. These results show the usefulness of PA imaging for monitoring not only photosensitizer accumulation and bleaching but also vascular responses in PDT with ICG-lactosome. This method can be applied to the diagnosis of many types of PDT processes.

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Hybrid UV laser direct writing of UV-curable PDMS thin film using aerosol jet printing

Hohnholz A., Obata K., Nakajima Y., Koch J., Terakawa M., Suttmann O., Overmeyer L.

Applied Physics A: Materials Science and Processing （Springer）  125 （ 2 ）  2019年02月

研究論文（学術雑誌）, 共著, 査読有り

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© 2019, Springer-Verlag GmbH Germany, part of Springer Nature. Polydimethylsiloxane (PDMS) is widely used for bio-medical, optical and microfluidic applications. Hence, PDMS layers on free-form surfaces on defined areas are needed. Conventional ways such as spin coating show drawbacks by long processing time and no sufficient application on free form surfaces. In this work, laser direct writing with UV-curable PDMS on a curved surface was performed. The coating technique using aerosol jet printing showed thin film thicknesses, compared to conventional spin coating techniques, obtaining controllable layer thickness down to 3.5 µm in 5 min on an area of 600 mm 2 and on non-flat surfaces. Deposition rate control achieved layer thicknesses between 3.5 and 25.7 µm. The combination of material deposition and x–y galvanometric mirror scanner-based laser direct writing leads to a hybrid approach aiming for several applications in the fields of surface functionalization, and bio-medical and sensory applications. In addition, the procedure is able to overcome the batch-based PDMS processing and introduce the continuous flow-based application.

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Biodegradability of poly(lactic-co-glycolic acid) irradiated with femtosecond laser pulses without material removal

Kondo N., Terakawa M.

Applied Physics A: Materials Science and Processing （Applied Physics A: Materials Science and Processing）  125 （ 2 ）  2019年

研究論文（学術雑誌）, 共著, 査読有り

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© 2019, Springer-Verlag GmbH Germany, part of Springer Nature. The degradation rates of biodegradable polymers are necessary to be controlled for tissue scaffold applications. In this work, we demonstrate that the degradation rate of poly(lactic-co-glycolic acid) (PLGA) was accelerated by irradiating with femtosecond laser pulses under the condition where material removal, i.e., laser ablation had not occurred. Scanning electron microscopy observation showed that the degradation rate was accelerated without significant laser ablation. The analysis of Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy revealed that the chemical properties of the PLGA had changed by femtosecond laser pulses irradiation. Furthermore, we have investigated the degradation of PLGA when the femtosecond laser pulses were focused inside the material. After the degradation, the PLGA showed enhanced optical scattering region in the depth of 300 µm from the surface. The results indicate that high-aspect-ratio modification and degradation are possible by changing the depth of focus of femtosecond laser pulses under the conditions where the direct removal of the material was not occurred.

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Surface-Enhanced Raman Spectroscopy (SERS) of Mancozeb and Thiamethoxam Assisted by Gold and Silver Nanostructures Produced by Laser Techniques on Paper

Atanasov P., Nedyalkov N., Fukata N., Jevasuwan W., Subramani T., Terakawa M., Nakajima Y.

Applied Spectroscopy （Applied Spectroscopy）  73 （ 3 ） 313 - 319 2019年

研究論文（学術雑誌）, 単著, 査読有り

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© The Author(s) 2018. Advanced gold (Au) and silver (Ag) nanostructures were produced by laser techniques on printer paper substrate. Surface-enhanced Raman spectroscopy (SERS) analyses of the fungicide mancozeb (Dithane DG) and insecticide thiamethoxam (Aktara 25 BG) in quantities smaller than usually applied in agricultural medicine were performed for the first time assisted by the structures fabricated. The investigations and results show an easy alternative and cheap way to detect small amounts or residue of harmful environmental pollutants, which has a direct bearing on food quality and thus on human health.

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Direct laser writing of Ag nanoparticle-composed structures in glass

Nedyalkov N., Koleva M., Stankova N., Nikov R., Atanasov P., Aleksandrov L., Iordanova R., Sliwinski G., Sawczak M., Grochowska K., Terakawa M.

Proceedings of SPIE - The International Society for Optical Engineering （Proceedings of SPIE - The International Society for Optical Engineering）  11047 2019年

研究論文（国際会議プロシーディングス）

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© 2019 SPIE. In this work results on laser assisted formation of silver nanoparticles in glass are presented. The sample material used in the experiments is Ag doped borosilicate glass fabricated by conventional melt quenching method. The glass samples are irradiated by nanosecond laser pulses at wavelength of 266 nm with a wide range of fluences and number of applied pulses. It is found that the laser radiation can lead to specific yellow coloration of the irradiated areas. The performed analyses show formation of silver nanoparticles in these zones. The optical properties of the irradiated areas are found to depend on the laser processing parameters and the silver concentration. The mechanism of nanoparticle formation is also discussed. The presented method can be used for formation of nanoparticles inside transparent materials and can be used for fabrication of novel materials with application in photonics.

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Strain sensing using electrically conductive structures composed of β-SiC fabricated by femtosecond laser direct modification of PDMS

Hayashi S., Nakajima Y., Terakawa M.

Proceedings of SPIE - The International Society for Optical Engineering （Proceedings of SPIE - The International Society for Optical Engineering）  10905 2019年

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© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. By femtosecond-laser-based modification of polydimethylsiloxane (PDMS), we fabricated an electrically conductive structure composed of β-silicon carbide (β-SiC) on a PDMS thin film for strain sensing. With an increase in applied strain, i.e. smaller bend radii of the conductive structures, the conductivity of the structure decreased significantly. The result indicates that the resistance of the conductive structure has high sensitivity to strain, leading to potential applications such as real-time monitoring of human motion.

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Femtosecond laser-based formation of electrically conductive silicon carbide on PDMS

Nakajima Y., Hayashi S., Katayama A., Nedyalkov N., Terakawa M.

Proceedings of SPIE - The International Society for Optical Engineering （Proceedings of SPIE - The International Society for Optical Engineering）  10908 2019年

　概要を見る

Copyright © 2019 SPIE. We experimentally demonstrated formation of electrically conductive structures by modifying native polydimethylsiloxane (PDMS) with femtosecond laser. By irradiating femtosecond laser pulses to native PDMS, black structures with electrical conductivity were formed. Analyses using X-ray diffraction (XRD) show that the formed structures were composed of β-silicon carbide (β-SiC). Our technique enables the spatially selective formation of β-SiC on the surface of PDMS, leading to open a novel route to develop a simple method to fabricate flexible or stretchable MEMS devices with SiC microstructures.

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Quality improvement of acoustic-resolution photoacoustic imaging of skin vasculature based on practical synthetic-aperture focusing and bandpass filtering

Tsunoi Y., Yoshimi K., Watanabe R., Kumai N., Terakawa M., Sato S.

Japanese Journal of Applied Physics （Japanese Journal of Applied Physics）  57 （ 12 ） 127001 2018年11月

研究論文（学術雑誌）, 単著, 査読有り

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© 2018 The Japan Society of Applied Physics. We previously developed a compact acoustic-resolution photoacoustic (PA) imaging system with optical fiber-based illumination, by which blood vessels in the rat skin were visualized in vivo. However, there were issues to be improved in the imaging characteristics: blurring in the out-of-focus region of the ultrasound sensor and degraded resolution due to low-frequency components in the PA signals. These are common limitations in acoustic-resolution PA imaging methods. In this study, we attempted to solve these problems by introducing signal processing methods based both on the synthetic-aperture focusing technique, which was applied only to signals in the detection zone of the sensor in the horizontal direction that was determined in advance in a phantom study, and on digital acoustic signal filtering with three specific frequency bands. Ex vivo and in vivo PA imaging of blood vessels in the rat skin and subcutaneous tissue showed the validity of the present signal processing methods.

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Femtosecond laser-based modification of PDMS to electrically conductive silicon carbide

Nakajima Y., Hayashi S., Katayama A., Nedyalkov N., Terakawa M.

Nanomaterials （Nanomaterials）  8 （ 7 ） 558 2018年07月

研究論文（学術雑誌）, 共著, 査読有り

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© 2018 by the authors. Licensee MDPI, Basel, Switzerland. In this paper, we experimentally demonstrate femtosecond laser direct writing of conductive structures on the surface of native polydimethylsiloxane (PDMS). Irradiation of femtosecond laser pulses modified the PDMS to black structures, which exhibit electrical conductivity. Fourier-transform infrared (FTIR) and X-ray diffraction (XRD) results show that the black structures were composed of β-silicon carbide (β-SiC), which can be attributed to the pyrolysis of the PDMS. The electrical conductivity was exhibited in limited laser power and scanning speed conditions. The technique we present enables the spatially selective formation of β-SiC on the surface of native PDMS only by irradiation of femtosecond laser pulses. Furthermore, this technique has the potential to open a novel route to simply fabricate flexible/stretchable MEMS devices with SiC microstructures.

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Femtosecond laser processing of biodegradable polymers

Terakawa M.

Applied Sciences (Switzerland) （Applied Sciences (Switzerland)）  8 （ 7 ） 1123 2018年07月

研究論文（学術雑誌）, 単著, 査読有り

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© 2018 by the authors. Biodegradable polymers have attracted increasing attention in tissue engineering and drug delivery systems owing to their high biocompatibility and biodegradability. Among the various methods for shape forming and modification of biodegradable polymers, laser processing has advantages in a dry processing approach that can process complex-shaped surfaces without using toxic chemical components. This review provides an overview of femtosecond laser processing of biodegradable polymers, especially in the last decade. The interaction mechanism of femtosecond laser pulse and biodegradable polymers, e.g., bond dissociation after laser irradiation, affects the degradable property of biodegradable polymers, which has the potential to control the degradation and sustainability of a structure. Applied studies on controlling cell behavior, tissue scaffolding, and drug release are also described.

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Gold nanoparticle-mediated laser stimulation induces a complex stress response in neuronal cells

Johannsmeier S., Heeger P., Terakawa M., Kalies S., Heisterkamp A., Ripken T., Heinemann D.

Scientific Reports （Scientific Reports）  8 （ 1 ） 6533 2018年04月

研究論文（学術雑誌）, 共著, 査読有り

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© 2018 The Author(s). Stimulation of neuronal cells generally resorts to electric signals. Recent advances in laser-based stimulation methods could present an alternative with superior spatiotemporal resolution. The avoidance of electronic crosstalk makes these methods attractive for in vivo therapeutic application. In particular, nano-mediators, such as gold nanoparticles, can be used to transfer the energy from a laser pulse to the cell membrane and subsequently activate excitable cells. Although the underlying mechanisms of neuronal activation have been widely unraveled, the overall effect on the targeted cell is not understood. Little is known about the physiological and pathophysiological impact of a laser pulse targeted onto nanoabsorbers on the cell membrane. Here, we analyzed the reaction of the neuronal murine cell line Neuro-2A and murine primary cortical neurons to gold nanoparticle mediated laser stimulation. Our study reveals a severe, complex and cell-type independent stress response after laser irradiation, emphasizing the need for a thorough assessment of this approach's efficacy and safety.

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Shrinkable silver diffraction grating fabricated inside a hydrogel using 522-nm femtosecond laser

Machida M., Nakajima Y., Torres-Mapa M., Heinemann D., Heisterkamp A., Terakawa M.

Scientific Reports （Scientific Reports）  8 （ 1 ） 187 2018年01月

研究論文（学術雑誌）, 共著, 査読有り

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© 2017 The Author(s). The integration of metal microstructures and soft materials is promising for the realization of novel optical and biomedical devices owing to the flexibility and biocompatibility of the latter. Nevertheless, the fabrication of three-dimensional metal structures within a soft material is still challenging. In this study, we demonstrate the fabrication of a silver diffraction grating inside a biocompatible poly(ethylene glycol) diacrylate (PEGDA) hydrogel by using a 522-nm femtosecond laser via multi-photon photoreduction of silver ions. The optical diffraction pattern obtained with the grating showed equally spaced diffraction spots, which indicated that a regular, periodic silver grating was formed. Notably, the distance between the diffraction spots changed when the water content in the hydrogel was reduced. The grating period decreased when the hydrogel shrank owing to the loss of water, but the straight shapes of the line structures were preserved, which demonstrated the optical tunability of the fabricated structure. Our results demonstrate the potential of the femtosecond laser-based photoreduction technique for the fabrication of novel tunable optical devices as well as highly precise structures.

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Femtosecond laser-triggered molecular release from biodegradable polymer microcapsules incorporated in gelatin hydrogel

Umemoto T., Terakawa M.

Proceedings of SPIE - The International Society for Optical Engineering （Proceedings of SPIE - The International Society for Optical Engineering）  10522 2018年

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© COPYRIGHT SPIE. Stimuli-responsible controlled release of growth factors from a tissue scaffold has gained significant interest for efficient tissue engineering. Laser-triggered methods for the molecular release have the advantage of spatial and temporal controllability. In this study, we demonstrate laser-triggered molecular release from biodegradable polymer microcapsules incorporated in gelatin hydrogel for the aim of efficient tissue engineering. The microcapsules, which fluorescent molecules were encapsulated, were fabricated using a dual-coaxial nozzle system. The microcapsule suspension was mixed with gelatin solution, followed by cross-linking to fabricate a gelatin hydrogel. Femtosecond laser pulses were focused onto the hydrogel to release fluorescent molecules from the microcapsules in the gelatin hydrogel.

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