Many intracellular proteins are catalysts that regulate cellular functions. These catalysts can be assayed to determine their functional state, but untii now it was not possible to simultaneously obtain a functional analysis and spatial data. Tony Ng, Anthony Squire, and others, working in the laboratories of Phillippe Bastiaens and Peter Parker, have combined Fluorescence Lifetime Imaging Microscopy (FLIM) with Fluorescence Resonance Energy Transfer (FRET) to spatially resolve the activation of a protein catalyst within living cells. Their technique was also applied to fixed cells.

Most electron microscopists appreciate that proper operation of the source is vital to the operation of the entire instrument. But because the gun involves a complex interplay of phenomena, few of which can be directly observed, some common misconceptions have gained currency — typically these "myths" contain a kernel of truth, but they can also mislead when accepted uncritically. In this series of articles, we explore three areas of common misunderstanding relative to operation of the thermionic {tungsten filament or LaB6) gun. (Field emitters are subject to very different considerations.)

Processes at real interfaces, such as drug dissolution, corrosion, enzyme activity and surfactant structure can now be studied with nanometer resolution using dynamic force microscopy. Optimal sensitivity is achieved when the tip is excited by direct application of a driving force using magnetic methods.

There are two distinct uses for holey carbon grids: for image checking and for support for ultrathin carbon films for cryo- EM. This procedure gives holes that are too large for convenient image checking, but are the appropriate size for support of carbon films. The procedure is divided into making the formvar mixture, dipping the slides and getting the film on the grids.

1) Take 45 mL of chloroform, add 0.2 g of formvar, and shake to dissolve. A small brawn glass jar with a capacity of 100 mL is the best container to use, and the jars from commercial formvar solution are ideal.

Questions have appeared on the microscopy listserver about how to prepare bacteria for SEM. This is an easy problem to solve, the greatest difficulty being preserving flagellae or pili. There are several references in basic EM texts, but briefly the bacteria can be treated as if they are small tissue samples, or negative staining samples for TEM. Details like of time in solutions, transition series, etc. will depend on the particular bacteria under study, and some trial and error will likely be needed. The procedures given here should give a reasonable starting point.

Recording images from the TEM with photographic film has a number of advantages over digital imaging. The first advantage is cost. Most institutions, whether academic or industrial, already have a darkroom so there is little or no start up cost. Even if a new darkroom must be equipped, a professional quality enlarger, lens, timer, paper cutter, paper safe, easel and safelight are easily under $2500 total. Trays and chemicals are inexpensive while an automatic print processor, which speeds up work significantly, while reducing exposure to chemicals, is about $2500. Additional lenses, so the same enlarger can be used for other film formats (35 mm), are about $200 each.

Geoff eloquently makes a case for film as opposed to digital image acquisition and processing. And while I agree with many of his points, I also have a slightly different point of view on several aspects.

Let's start with the darkroom. While Geoff is correct in saying that many institutions already have a darkroom or have access to one at no cost, this only tends to hide the cost. Somebody has to build the darkroom and somebody has to pay for building maintainingand equipping the darkroom. If this is paid out of some overhead and not paid for directly, then the cost is hidden in that overhead, which would be less without the darkroom.

Questions have arisen recently on the Histonet listserver about the properties of zinc formalin fixative. The advantage of zinc formalin over the usual formalin fixatives appears to be that zinc ions hold macromolecules in their native conformation via coordinate bonds, preventing the damaging crosslinkages that formaldehyde alone would create. The result is greatly enhanced immunopreservation: rarely is antigen retrieval necessary, and primary antibodies can be diluted 2 to 10 fold greater than usual.

FT-IR (Fourier Transform Infrared) spectroscopy is an instrumental technique for measuring the infrared spectrum of materials. Many organic compounds have characteristic spectra that can be used for their identification, and specific functional groups (hydroxyl, carbonyl. amine, etc.) have characteristic bands at certain frequencies.

Microscopes have been coupled to FT-IR instruments and allow the IR spectrum determination of single particles. This greatly increases the identification possibilities of small particles and contaminants. These particles can be mounted on sodium chloride or potassium bromide salt crystals, since these materials are transparent to infrared radiation.