Ionic liquid-based transmission electron microscopy for herpes simplex virus type 1
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LETTER TO THE EDITOR
Ionic liquid-based transmission electron microscopy for herpes simplex virus type 1 Tetsuya Tsuda 1
&
Koshi Kawakami 1 & Eiko Mochizuki 1 & Susumu Kuwabata 1
Received: 29 March 2018 / Accepted: 2 April 2018 # International Union for Pure and Applied Biophysics (IUPAB) and Springer-Verlag GmbH Germany, part of Springer Nature 2018
Keywords Ionic liquid . Transmission electron microscopy . Biological specimens . Kamlet-Taft parameters . Herpes simplex virus type 1
Introduction Ionic liquid (IL), which is often called room-temperature ionic liquid, ambient-temperature ionic liquid, and ambienttemperature molten salts, is a liquid salt composed entirely of cations and anions, and it melts below 298 K without any solvents. It is expected to be an innovative liquid material and a functional solvent due to its interesting physicochemical properties such as flame resistance, relatively high conductivity, negligible vapor pressure, and antistatic properties. Various next-generation applications in science and technology with IL have been proposed to date (Torimoto et al. 2010; Wasserscheid and Welton 2008; Eftekhari 2017). In 2006, it was reported that IL droplets could be observed by scanning electron microscopy (SEM) without charging behavior (Kuwabata et al. 2006). Subsequent efforts are being made to develop novel IL-based electron microscopy techniques to capitalize on the fact that a thin IL layer spread on insulating materials and biological specimens works as a conductive layer, similar to a thin gold or carbon layer (Torimoto et al. 2010; Tsuda et al. 2011; Eftekhari 2017). In this study, a facile ILbased pretreatment method for transmission electron microscopy (TEM) observation of herpes simplex virus type 1 (HSV) is suggested as an alternative to a conventional, complicated, and
laborious pretreatment protocol. The aim of this study is to explore a relationship between the IL species and the resulting TEM images by using Kamlet-Taft parameters.
Materials and methods The preparation and purification methods of ILs, such as 1-ethyl3-methylimidazolium tetrafluoroborate ([EtMeIm][BF4]) and choline lactate ([Ch][CH3CH(OH)CO2]), used in this study have been described in a previous article in detail (Tsuda et al. 2011). The TEM observation was conducted by a Hitachi H-7650. The IL-based pretreatment protocol for TEM observation of HSV and liposome is depicted in Scheme 1. The polarity factors of the ILs to be used for the pretreatment process were determined from the UV-Vis data of ILs with dyes and the equations for obtaining Kamlet-Taft parameters (Reichardt 1994; Fukaya et al. 2007; Lee et al. 2008). The dyes used were Reichardt’s dye (90%, Sigma-Aldrich), 4-nitroaniline (> 99%, Wako) and N,N-diethyl-4-nitroaniline (97%, Wako). The UV-Vis spectroscopy was conducted at room temperature (ca. 298 K). The HSV was supplied by Professor Yasuo Suda’s laboratory (Kagoshima University, Japan). The liposome was prepared by vigorously agitating a 22.7 g L−1 COATSOME EL-01-N (NOF) aqueous solution an
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