A Simple Preparation of Graphite-coated Grids for High Resolution Electron Microscopy

High resolution electron microscopy requires that the specimen supports be smooth. With this in mind a procedure was developed for cleaving single graphite crystals into thin flakes suitable as specimen supports. Fernfindez-Morfin (1) was the first to use graphite and mica crystals for specimen supports. He as well as Sprague (2) obtained the thin sheets of mica and graphite required through successive cleavages of single crystals by attaching adhesives or plastics to each side of the crystal and then pulling these apart. We have found the complete removal of the adhesive virtually impossible. In this note we report a method in which no adhesives are used, and smooth, clean, thin graphite fihns are readily obtained. Single crystals of graphite are obtained from marble embedded with graphite (2). This is mined in Essex County, New York, and can be purchased through Ward's Natural Science Establishment, Inc., Rochester, New York. Concentrated nitric acid dissolves the marble, leaving the graphite and a small amount of quartz. This residue is washed in tap water. A drop of clean ethanol is put on a clean, glass microscope slide. A good, unfragmented, smooth, graphite crystal is placed on the drop of ethanol. Another slide is placed over this, and the sandwich is lowered into liquid nitrogen and left there until the rapid boiling ceases. The glass-graphite sandwich is then removed and the glass slides are forced apart. I t is found that the frozen ethanol acts as an adhesive and the graphite is cleaved, leaving part of the crystal attached to each glass slide. The glass slides are allowed to warm up, the condensed water removed, another drop of ethanol placed on each crystal, and the procedure repeated. Successive splittings are continued until at least a portion of the crystal is sufficiently thin to be light grey. Such flakes are then floated off on water after much of the ethanol has evaporated, but before the condensed water has completely dried off. The graphite flakes then can be picked up on grids coated with polybutene (3). During one afternoon perhaps two dozen graphitecoated grids can be prepared with a litde practice. Light grey flakes are thin enough for high resolution microscopy. The adsorption properties appear to be similar to those of evaporated carbon and the graphite grids can be used for the recovery of long DNA molecules in a manner similar to that described previously (4). Quanti tat ive aspects of the improvement in background are now under investigation.