ResiTAG™ – A Novel Sample Identifi cation Solution for Microscopists and EM Facilities

Bronwen Forward , George Vaniotis ,* and Gourgen George Ambartsoumian GA International , 3208 Jacques-Bureau Avenue , Laval , Québec H7P 0A9 , Canada


Abstract: Electron microscopy requires the use of resin-embedded samples in order to obtain ultra-thin sections for imaging. However, the identifi cation of these resin capsules and molds can be challenging, as traditional inks will run or smear during the embedding process. This can often lead to sample mix-ups or loss of information. This article describes a novel identifi cation solution, ResiTAG™ , specifi cally designed for use with resin capsules and molds. The article details how this chemical- resistant label can be incorporated into the sample preparation process.

Keywords: Electron microscopy, sectioning , resin , label , identifi cation

Introduction T e study of the cell, the basic unit of life, is a key point of research. As such, researchers have long sought to uncover what occurs at the cellular level within tissues to better understand how they function. Whether studying the eff ects of a drug treatment on a strain of bacteria or determining cellular diff er- ences between healthy and diseased tissues, it is oſt en necessary to understand the structural biology of the cell. To this end, microscopy techniques and instruments play an important part in helping us visualize what is happening in the cell. While imaging technologies have advanced substantially, methods for sample identifi cation have remained relatively unsophisti- cated. T is article describes a modern approach to microscopy specimen labeling. Microscopy . T ere are three main branches of microscopy: light, electron, and scanning probe microscopies. Each of the three serve a particular purpose. Advances in microscopy revolutionized the study of biology and gave rise to the histology fi eld. Microscopy techniques have proven equally important and benefi cial in the basic research laboratory as in the clinical environment. Microscopy sample preparation . Samples used in microscopy can be collected from a variety of sources, from biopsies taken from human patients to cells grown under laboratory conditions. Regardless of the source, however, biological samples typically must be chemically fi xed and embedded in a structurally supportive media prior to the production of thin sections for observation under the microscope [ 1 ]. T e type and size of the tissue being studied, and the level of ultrastructural detail required, will determine the type of microscope to be employed as well as the fi xation agent and embedding media needed to achieve the best imaging results. T e two most common fi xatives are formal- dehyde and glutaraldehyde, with the latter being better suited for electron microscopy, as it off ers a more rigid fi xed product. T ere are two primary means of embedding tissue for sectioning; paraffi n wax and resin. In addition, cryo-microscopy techniques are becoming quite important, where special equipment is used to section fi xed and unfi xed sections at cryogenic temperatures. Light microscopy specimens . Paraffi n wax embedding for light microscopy is the most commonly used medium, chosen for its versatility and relative ease of preparation. T e embedding process involves multiple processing stages from


dehydration, to clearing, infi ltration, and fi nally embedding in the desired medium [ 2 ]. Following fi xation in formalin or glutaraldehyde, water is removed from the tissue by slowly replacing it with ethanol. T is is followed by a clearing agent, such as xylene to remove the alcohol, before the paraffi n infi ltration agent replaces the clearing agent. T e paraffi n wax blocks for histology are microtomed to 4 µm thick sections and placed on glass slides. T ere are few drawbacks to this popular method, although to observe the fi ne details of organelles, the better image resolution of electron microscopy is needed. Electron microscopy specimens . Transmission electron microscopes (TEMs) operating at 100 kV require specimens thinner than 0.1 µm, typically 30 to 60 nm for the best image resolution [ 3 ]. In the case of electron microscopy, an epoxy resin embedding medium is recommended because it will form a hard matrix once cured at 60C, allowing for thinner sections to be cut with an ultramicrotome. T ese thin specimens can then be observed in a TEM, allowing visualization of cellular structures down to the nanometer scale ( Figure 1 ). T icker sections can still be obtained from resin-embedded tissue for use in light microscopy if desired. T e use of TEM is ideal for investigating the ultrastructure of the cell organelles. Sample identifi cation . One of the most critical aspects of any experiment is sample identifi cation, particularly for thin

Figure 1 : Example electron micrograph of an ultrathin section of the ventricular muscle of group II (diabetic rats) showing margination of the nuclear chromatin of a nucleus of a cardiac myocyte (arrows). Myo-fi brils appear completely rarefi ed (r). Most mitochondria show dense matrix (m) while others show disrupted cristea (arrowhead) (original mag. 4000×). Image copyright © MM Dallak et al.[ 5 ]

doi: 10.1017/S155192951800086X • 2018 September

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