title: Infrared Microspectroscopy of Bionanomaterials (Diatoms) with Careful Evaluation of Void Effects.
abstract: In order to characterize a representative natural bionanomaterial, present day centric diatom samples (diameter, 175-310 µm) have been analyzed and imaged by infrared (IR) micro-spectroscopy and scanning electron microscopy (SEM). Because diatom silica frustules have complex microscopic morphology, including many void areas such as micro- or nano-pores, the effects of voids on the spectral band shapes were first evaluated. With increasing void area percentage, 1220 cm(-1)/1070 cm(-1) peak height ratio (Si-O polymerization index) increases and 950 cm(-1)/800 cm(-1) peak height ratio (Si-OH/Si-O-Si) decreases, both approaching 1. Based on the void area percentage of representative diatom samples determined using SEM image analyses (51.5% to 20.5%) and spectral simulation, the 1220 cm(-1)/1070 cm(-1) ratios of diatom samples are sometimes affected by the void effect, but the 950 cm(-1)/800 cm(-1) ratios can indicate real structural information of silica. This void effect should be carefully evaluated for IR micro-spectroscopy of micro-nano-porous materials. Maturity of diatom specimens may be evaluated from: (1) void area percentages determined by SEM; (2) average thicknesses determined by optical microscope; and (3) average values of 1220 cm(-1)/1070 cm(-1) peak height ratios (opposite trend to the void effect) determined by IR micro-spectroscopy. Microscopic heterogeneities of chemical structures of silica were obtained by IR micro-spectroscopic mapping of four representative diatoms. The 950 cm(-1)/800 cm(-1) ratios show that large regions of some diatoms consist of hydrated amorphous immature silica. The successful analysis of diatoms by IR micro-spectroscopic data with careful void effect evaluation may be applied to physicochemical structures of many other bionanomaterials.
authors.affiliation: Department of Earth and Space Science, Osaka University, Toyonaka, Japan.
authors.forename: Leila
authors.initials: L
authors.lastname: Alipour
authors.affiliation: Department of Earth and Space Science, Osaka University, Toyonaka, Japan.
authors.forename: Mai
authors.initials: M
authors.lastname: Hamamoto
authors.affiliation: Department of Earth and Space Science, Osaka University, Toyonaka, Japan satoru@ess.sci.osaka-u.ac.jp.
authors.forename: Satoru
authors.initials: S
authors.lastname: Nakashima
authors.affiliation: Thermo Fisher Scientific Corp., Nishinakajima 6-3-14, Osaka, Japan.
authors.forename: Rika
authors.initials: R
authors.lastname: Harui
authors.affiliation: Hitachi High Technologies Corp., Miyahara 3-3-31, Osaka, Japan.
authors.forename: Masanari
authors.initials: M
authors.lastname: Furiki
authors.affiliation: Micro World Service. Minami-Otsuka 1-3-25-301, Tokyo, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Oku
mesh_terms: D017377:Diatoms / Q000737:chemistry* / Q000648:ultrastructure*; D008855:Microscopy, Electron, Scanning; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D016062:Porosity; D012822:Silicon Dioxide / Q000737:chemistry*; D013055:Spectrophotometry, Infrared
chemical_list: D012822:Silicon Dioxide
keywords: Bionanomaterial; Diatom; Infrared (IR) microspectroscopy; Scanning electron microscopy (SEM); Void effect