Preparation and Microstructure Control of Protein Thin Films Deposited by Pulsed Laser Deposition and Via Colloid Chemic
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PREPARATION AND MICROSTRUCTURE CONTROL OF PROTEIN THIN FILMS DEPOSITED BY PULSED LASER DEPOSITION AND VIA COLLOID CHEMICAL ROUTES Sayuri Nakayama 1), Ichiro Taketani 1), Sanshiro Nagare 2), Mamoru Senna 1) 1) Keio University, Faculty of Science and Technology, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan 2) Nara Machinery Co., Ltd., 2-5-7 Jonan-jima, Ohta-ku, Tokyo, 143-0002, Japan ABSTRACT Protein thin film (mainly silk fibroin) was prepared by pulsed laser deposition (PLD) with 1064nm IR-beam and via colloid chemical routes. Thickness, surface roughness, and microstructures of the deposited film were examined by quartz crystal microbalance sensor, field emission scanning electron microscope (FE-SEM), and atomic force microscope (AFM). The laser power density was varied systematically for PLD to control the microstructures of the film and the secondary structure (β-sheet, α-helix, or random coil) of the protein. Secondary structure of the target and film was examined by FT-IR. Films prepared by PLD comprise by agglomerated particles with their primary particle size around 30nm. The size of the primary particles was uniform, especially for the film prepared at low laser power density. At low laser power density, proportion of β-sheet increased and that of random coil decreased. Proportion of random coil was also increased by the wet colloidal process. PLD with low power density is most suitable to preserve the secondary structure in the protein thin film. INTRODUCTION Preparation of protein thin films is gaining increased interest for applications in biomaterials such as biosensors or surface modification of implant materials. Pulsed laser deposition (PLD) is one of the most popular methods for thin film preparation [1-3]. Tsuboi et al. have triggered its application to protein films in 1998 [4]. They have used silk fibroin, main component of silk having a simple primary structure, as the target protein and studied the preservation of secondary structures after PLD. Excimer lasers with wavelength in the UV region, e.g. 248nm and 351nm, were used with photosensitizers to preserve the secondary structures of silk fibroin [4-7]. In this work, we used silk fibroin as target protein but with laser wavelength of 1064nm, in the IR region, having relatively low photon energy, for the purpose of preserving the secondary structure of silk fibroin without any photosensitizers. Effects of laser fluence on the surface morphology and secondary structures were examined. We also compare the physical and chemical properties of the films with those deposited via colloid chemical routes.
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EXPERIMENTAL A silk fibroin (SF) target was prepared by hot pressing 2g of SF powder (Lot: 98, donated by Idemitsu Petrochemical Inc., with β-sheet structure, and average particle size of 7.9µm) under 80oC and 10MPa for 30min. Nd: YAG laser at wavelength of 1064nm, pulse width of 5ns, and repetition rate of 10Hz, was used as the laser source. Laser power density was varied systematically between 0.5 and 50J/cm2. On the other
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