Nanostructure analysis of protein thin film prepared by wet and dry processes
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KK3.10.1
Nanostructure analysis of protein thin film prepared by wet and dry processes I. Taketani*, S. Nakayama*, S. Nagare**, M. Senna* *Keio University, Faculty of Science and Technology, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan TEL: 045-566-1589, FAX: 045-564-0950, e-mail: [email protected] **Nara Machinery Co.,Ltd., 2-5-7 Jonan-jima, Ohta-ku, Tokyo, 143-0002, Japan ABSTRACT Silk fibroin (SF) and bovine serum albumin (BSA) thin films were deposited on Si(100) substrate either by colloid casting method or by pulsed laser deposition (PLD). Emphasis is laid on the comparison of nanostructures, which developed during the deposition. AFM diagrams were evaluated to quantify the nanostructures, parallel and perpendicular to the substrate, by the average wavelength of the profilogram (Wa) and surface roughness (Rrms), respectively. The film thickness increased with increasing the concentration of colloids or laser deposition time. The value of Wa increased with the film thickness. We note, however, that the value Wa becomes much less sensitive with decreasing the scanning area due to decreasing probability of the abnormally large agglomerates of the nanometric units. Probability of the agglomeration growth as a consequence of the surface adhesion is higher with higher concentration of random coil, followed by β-sheet and α-helix. BSA with smaller primary units and lower probability of agglomeration give more uniform films. INTRODUCTION Preparation of protein thin films gathers increasing interests in the field of biomaterials, e.g., biosensors or surface modification of implant materials [1-3]. Since a close relationship between the function and the secondary structure of protein is well known, to control of the secondary structure and agglomeration of units in the thin film is essential, together with the well-defined thickness and continuity of the films, for the purpose of practical application [4-6]. Silk fibroin (SF) and bovine serum albumin (BSA) are familiar and well worked-out so that surface coating and thin films of SF and BSA are applied to biomedical and biotechnological fields [5]. In this work, SF and BSA thin films are prepared via colloid chemical routes and compared with those made by pulsed laser deposition (PLD). Emphasis is laid to compare the states of agglomeration composing nanometric units in the films, by evaluating AFM images. We also try to elucidate the relationship between the agglomeration behavior and the secondary structure of the protein.
KK3.10.2
EXPERIMENTAL DETAILS Intact SF powder was donated by Idemitsu Petrochemical Inc., Lot: 98, with β -sheet structure, and average particle size of 7.9µm. SF powders were degummed by refluxing with 0.5 wt% aqueous solution of Na2CO3 for 30 minutes, stirred and then centrifuged. A mixture of degummed SF powder and CaCl2 in EtOH + H2O solution was refluxed for 20 minutes to dissolve the fibroin. CaCl2 was then removed by dialyzing for 3 days. BSA solutions were prepared by dissolving BSA powder (Sigma Aldrich) in deionized water.
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