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Initiating New Research Collaborations

To discuss new collaborations with the Laboratory of Bioengineering and Physical Science, contact: Dr. R.D. Leapman

Often, the key to a successful project is the use of appropriate specimen preparation methods. Measurement of subcellular ion concentrations by analytical electron microscopy requires specialized rapid-freezing and cryosectioning methods because conventional procedures result in loss of intrinsic elements and introduction of extraneous ones by fixation, embedding and staining.

Quantitative mass measurements of isolated supramolecular assemblies using scanning transmission electron microscopy (STEM) mass requires the use of ultrathin carbon support films. High-resolution imaging of cells often requires rapid freezing techniques to preserve native structures as well as the distributions of tightly bound elements. Hyperbaric freezing and freeze-substitution are very useful in such applications because samples can be embedded in plastic and sectioned in the standard way. The group puts a major effort in developing preparation methods and has established considerable expertise on the subject, starting with treatment of tissues, cell cultures, or suspensions of macromolecules.

The nanoscale analytical instrumentation available in the resource is capable of high sensitivity (a few atoms for some analyses). However, it is important to realize that the analytical EM is best suited to detect small numbers of atoms in highly localized regions of the specimen (typically 10-100 nm diameters). Generally the sensitivity is not in the micromolar range. In fact, an organelle of diameter 50 nm with an ionic concentration of 100 micromolar contains only 6 ions! Analytical EM measures total ion concentrations rather than free ion concentrations, so in this respect the technique is complementary to optical fluorescence techniques.