Cold stage design for high resolution electron microscopy of biological materials

Both the number and range of applications of cryotechniques in transmission electron microscopy are increasing rapidly. In some cases, most notably the determination of protein structure by electron crystallography, progress has been limited by the performance of commercially available cryo stages. We review the design and performance criteria for stages which will be necessary for wide applicability in high resolution studies of biological specimens. The important criteria include an operating temperature below -140 degrees C with a low rate of contamination of the specimen, ability to tilt to 60 degrees, and perhaps most important, good resolution as judged by an effective modulation transfer function of 0.8 at 0.35 nm. Most applications also require an effective cryotransfer system. Up until now, most work in high resolution electron crystallography has been accomplished with laboratory-built stages which meet some, but not all, of these criteria. The availability of cold stages which fully meet criteria will allow the rapid expansion of high resolution studies by electron microscopy in structural biology.