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.

Water adsorption with relative humidity changes for keratin and collagen as studied by infrared (IR) micro‐spectroscopy

“…All the spectra were obtained by accumulating 64 scans at a wavenumber resolution of 4 cm −1 . The transflection method has been reported to be used quantitatively in IR micro‐spectroscopy …”

Decrease of aliphatic CHs from diatoms by in situ heating infrared microspectroscopy

“…The best fits of our data for aliphatic CH decreases at 300°C to the two first‐order reaction equations are shown in Figure (correlation coefficient R > 0.991). We have tried to keep constant C 1 , C 2 , and C 3 values or their proportions in the fittings, but could not get good fits, because of heterogeneities in chemical compositions and maturities of each diatom sample [ Alipour et al ., ]. Obtained first‐order rate constants for aliphatic CH at 300–260°C including generally errors of less than 15% are listed in Tables and .…”

Visualization of elemental distributions and local analysis of element-specific chemical states of an Arachnoidiscus sp. frustule using soft X-ray spectromicroscopy

“…As shown in Fig 4a, we selected three ROIs, red, green and blue ROIs, as shown in the figure. For the cases of Si and O, the red ROIs [3,13,19]. (b) Scheme for recording the O K-XAS spectrum using a series of X-PEEM images acquired by sweeping the energy of the incident photon beam across the O K-edge (upper half).…”

“…Diatoms are a major group of eukaryotic unicellular microalgae with characteristic cell walls composed of a composite of organic material and nanoporous hydrogenated amorphous silica, referred to as frustules [1][2][3]. Similar to terrestrial plants, diatoms play a crucial role in carbon fixation and generate approximately 20% of the oxygen produced on Earth each year by photosynthesis [4,5].…”

“…However, since the invention of the electron microscope in the first half of the 20th century, many morphological studies have been conducted on diatoms, especially on the micro-/nanostructure of their frustules. Currently, to examine the micro-/nanostructural features of diatom frustules, various microscopic and spectromicroscopic methods, including optical microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) [3,[12][13][14][15][16][17][18][19][20][21], atomic force microscopy (AFM) [12,[14][15][16]19], transmission X-ray microscopy (TXM) [22,23], microprobe X-ray fluorescence (μXRF) analysis [24,25], and infrared (IR) microspectroscopy [3], are used to investigate diatoms.…”