Conductivity Preparation by Choline Lactate Ethanol Solution for SEM Ob servation: Both Hard and Soft Tissues in Living Matter

18 Introduction Choline, a well-known neurotransmitter, consists of a tetraammonium cation that has three methyl groups symmetrically and a hydroxyethy group, and some anion molecules (shown in Scheme 1). Some of the organic salts, such as choline lactate, have specific physical properties such as noncombustibility, extremely low vapor pressure, high heat resistance, and high ionic conductivity. Choline lactate also has a unique property, i.e., it is liquid at room temperature, a so-called room temperature ionic liquid (RTIL). Because of these properties, RTILs have attracted much attention for application in many fields [1-4]. Recently, Kuwabata et al. applied an imidazolium-type RTIL for pre-treatment of a scanning electron microscope (SEM) observation because the ionic liquid has some suitable properties for the treatment described above. They observed SEM images of biological specimens such as insect, flower, tissue, pollen, and cell using several IL aqueous solutions [5]. To estimate the usefulness of the pretreatment, we applied imidazolium-type ILs for nanocarbon materials such as fullerene nanocrystals and carbon nanotubes. The highest resolution observed was <30 nm [6]. For improvement the affinity of ILs to biological materials, we designed novel choline-type ILs and applied for SEM observation Conductivity Preparation by Choline Lactate Ethanol Solution for SEM Observation: Both Hard and Soft Tissues in Living Matter