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

Tomoko Ishihara,Masaki Oura,Yoshinori Kotani,Akinobu Yamaguchi,Takuo Ohkochi,Wanli Yang

doi:10.1371/journal.pone.0243874

Abstract

Using soft X-ray (SX) spectromicroscopy, we show maps of the spatial distribution of constituent elements and local analysis of the density of states (DOS) related to the element-specific chemical states of diatom frustules, which are composed of naturally grown nanostructured hydrogenated amorphous silica. We applied X-ray photoemission electron microscopy (X-PEEM) as well as microprobe X-ray fluorescence (μXRF) analysis to characterize the surfaces of diatom frustules by means of X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES). We successfully demonstrated that SX spectromicroscopy is able to participate in potential observation tools as a new method to spectroscopically investigate diatom frustules.

Highlights

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]
X-ray photoemission electron microscopy (X-PEEM), which is classified as a full-field microscopy using an electrostatic lens system, is based on the photon-IN/electron-OUT measurement scheme of measuring electrons to generate an image of the sample surface, whereas scanning soft X-ray (SX) spectromicroscope relies on the photon-IN/photon-OUT measurement scheme to generate an image of the sample surface
There are some bright spots in the image that are considered to originate from the sample itself or from the dust attached on the frustule surface, not from instrumental factors such as bad pixels

Summary

Introduction

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]. In addition to being photosynthetic organisms, diatoms are thought to play a key role in the production of useful substances, and research on various applications (see, for example, a review by Mishra et al [7]) is being widely conducted by taking advantage of the potential of diatoms [8,9,10,11]. Diatoms can be roughly classified into two distinct shapes: most of them are broadly bilaterally symmetric (pennate diatoms), while a few of them are radially symmetric (centric diatoms).

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Conclusion