All of us have looked at leaves. They're interesting. Some of us have looked at leaves under a light microscope. Still interesting. Some have looked at leaves under more powerful microscopes, and apparently they found it interesting still. Now some folks have looked more closely than ever before, and guess what? This may be the most interesting! Wendy Mechaber, Durwood Marshall, and Frances Chew of Tufts University, Richard Mechaber of GEI Consultants, Inc., and Renee Jobe of TopoMetrix turned to the atomic force microscope (AFM) to analyze the landscape of the surfaces of leaves, apparently for the first time.

Recent Internet postings on the Microscopy listserver indicate paradoxical views on the personal protective equipment (PPE) necessary to handle liquid nitrogen (LN2) safely. Those views range from full protective gear to, somewhat facetiously, complete nudity. The crux of the paradox is that both extremes have points of validity.

The gist of preventing frostbite or cold injury to the skin is to prevent continuous contact with LN2. The physics of the Leidenfrost effect (LE) protects the skin from momentary contact or splashes of LN2. A layer of gas between the LM2 and the skin prevents significant heat transfer from the skin, stopping damage. The LE does not apply to inadvertent splashes of LN2 to the cornea. Alternatively, using protective equipment insulates the skin and prevents trapping of the cryogen by allowing the LN2 to run off.

Most of us have used fluorescence microscopy and are all too familiar with the advantages and disadvantages of this tool: easy identification of one or more labels that fluoresce at different wavelengths (color) against the relatively dark background of the biologic substrate, but we can't always get the spatial resolution that is needed to answer our questions. Electron microscopy, both transmission and scanning modes, offer much better spatial resolution, but present problems in localizing a label, particularly on the surface of a cell. Wouldn't it be great if an imaging technique were available that gave us the possibility of localizing one or more labels on the surface of a cell with resolution approaching electron microscopy. Karen Hedberg, Bruce Birrel, Douglas Habliston, and Hayes Griffith at the University of Oregon describe photoelectron imaging as the electron optical analogue of fluorescence microscopy, offering some of the advantages of both methods.

Neurons are about as polarized as cells ever get. Their axonal process can extend a distance that is up to a million times the diameter of the nerve cell body. Axons have none of the ribosomal machinery responsible for protein synthesis, so all neuronal proteins and peptides must be manufactured near the nucleus and carried out to the periphery. This distribution involves at least two distinct mechanisms, fast axonal transport, moving at almost 500 mm per day, and slow axonal transport, moving only 0.1 to 3 mm per day. It turns out that proteins of the neuronal cytoskeleton, along with many soluble cytosolic proteins, are transported exclusively by the slower process.

If you have been hibernating for several weeks you may have missed the headlines and magazine covers exclaiming about “Life on Mars!” The basis for all of this excitement is an article in Science by Dr. David S. McKay of the Lyndon B. Johnson Space Center in Houston and eight of his colleagues from several academic institutions. The reader of this column will not be surprised by the fact that microscopes were used to detect evidence of life on a meteorite from Mars.

The first consideration was whether or not the meteorite was in fact a fragment of the martian surface. The specimen, known as ALH84001, is from a class of meteorites that appear to have resulted from impacts on Mars, some of the specimens landing in Antarctica where this one was recovered. Trapped gases (in glass droplets and stringers) in several of the family of meteorites closely match the martian atmosphere for several gases over 8 orders of magnitude range in abundance. Whereas ALHB4001 did not contain such trapped atmospheric gases, its elemental and isotopic composition closely resemble the meteorites that do.

Recent Internet postings on the Microscopy listserver indicate paradoxical views on the personal protective equipment (PPE) necessary to handle liquid nitrogen (LN2) safely. Those views range from full protective gear to, somewhat facetiously, complete nudity. The crux of the paradox is that both extremes have points of validity.

The gist of preventing frostbite or cold injury to the skin is to prevent continuous contact with LN2. The physics of the Leidenfrost effect (LE) protects the skin from momentary contact or splashes of LN2. A layer of gas between the LN2 and the skin prevents significant heat transfer from the skin, stopping damage. The LE does not apply to inadvertent splashes of LN2 to the cornea. Alternatively, using protective equipment insulates the skin and prevents trapping of the cryogen by allowing the LN2 to run off.

The process of ultra-miniaturization has been termed nanofabrication. It looks like the scanning tunneling microscope (STU) and related microscopes will be players in this technology of the future. One of the most recent contributions has been the demonstration that single molecules can be “pushed” across a surface with the STM. This remarkable achievement was demonstrated by Thomas Jung, Reto Schlittler, and James Gimzewski of the IBM Zurich Research Laboratory and Hao Tang and Christian Joachim of the National Center for Scientific Research in Toulouse, They were able to position intact individual molecules on a two-dimensional surface at room temperature by a controlled “pushing” action of the tip of a STM. Similar positioning feats have been done at low temperatures while thermal motion is limited.

It is impressive enough that individual atoms can be resolved with the atomic force microscope (AFM), but who would have thought that atomic motion would be detected so soon? Atomic resolution with the AFM was only recently achieved. As reported in this column, Franz Giessibl was able to demonstrate local resolution of adatoms of the Si(111) 7×7 reconstructed surface. Now, Yasuhiro Sugawara. Masahiro Ohta, Hitoshi Ueyama, and Seizo Morita of Hiroshima University have demonstrated atomic resolution of the surface of InP(110). Not only that, but images taken about one minute apart show that some of the atoms had moved! Sugawara et al, used a very compact AFM under ultrahigh vacuum (4 X 10-8 Pa) to accomplish this impressive feat. A stiff (spring constant of 34 N/m) silicon cantilever was used. This stiffness, along with a mechanical resonant frequency of 151 kHz, was used to keep the cantilever from jumping onto the sample and crushing the initially sharp tip.

We know from the pictographic history that the people in ancient Egypt were fond of beer and bread. Fortunately, they sent samples of these food items along with some of their more esteemed citizens to sustain them in the afterlife. Also, samples were available from rubbish heaps of ancient villages, allowing for the comparison of funerary goods with everyday foods. Additional luck was that the dry conditions have kept some samples from deteriorating even after thousands of years. Whereas they did leave us samples, they didn't leave recipes. There have been many theories about how they brewed and baked in ancient Egypt, but proof was lacking. Recently, Delwen Samuel of Cambridge University used optical and scanning electron microscopy (SEM) to determine how the ancient Egyptians brewed beer and baked bread.

It has been noted by many people who have had the privilege of exploring Mayan ruins that there is a stunning blue color that has been preserved amazing well for centuries. Considering the tropical jungle is quite a hostile environment, the tenacity of this “paint” is remarkable. It had been suggested that this “paint” was made by mixing indigo dye with clay, but this did not explain its special characteristics. Recent work by Miguel José-Yacamán at the National University of Mexico and colleagues has revealed what is special about this material, which is called Maya blue paint. They collected specimens in Mexico at archeologic sites known as Jaina Island and Palenque.

The particle size of organic pigments used in modern coatings is extremely fine. Since these individual pigment crystals are typically less than 1 μm in size, they are difficult, if not impossible, to characterize and identify by microscopical means. The occurrence of occasional pigment aggregates may help identify a pigment to a microscopist who is familiar with a variety of known pigments under controlled conditions. More often, however, such observations provide a qualitative basis for comparison of questioned and known paints without leading to identification of the specific pigments involved. Microscopic observations of this type are assisted by the use of a high-magnification oil immersion objective and condenser with numerical apertures of 1.25 or greater.

Over the years, efficiency of backscattered electron detectors has improved. Robinson has developed a unique system whereby two BSE detectors are used, offering an array of benefits to the SEM operator. The system consists of two detectors with scintillators of dedicated geometrical shape, providing a collection area greater than 2000 mm2. They are situated against the axis of the electron beam, with the right and left signals combining to form the overall image signal - one that is 1.5 times greater than that of a single detector. The omnidirectional image illumination, similar to that attained thorough a traditional SE detector, prevents shadowing due to the 180° collection angle.

The electron microscope has evolved to the level where it is now straightforward to record high-resolution images from thin samples (t~ to 20 nm) that are directly interpretable in terms of atomic arrangements. Whilst recorded images necessarily represent two-dimensional projections of the structure, many defects such as dislocations and interfaces may be linear or planar in nature and this might be expected to be amenable to detailed characterization. In this review, we briefly consider the recent significant progress that has been made in quantitative defect analysis using the high-resolution electron microscope and then discuss some drawbacks to the technique as well as potential scope for further improvements.

As the need for prefixes for 10-21 and 10-24 arose, “zepto” and “yocto” surfaced. Professor Dovichi, a leader in ultramicroanalytical techniques, jokingly suggested that these units have been named in honor of two lesser known Marx brothers. Indeed, the habits of the International Committee of Weights and Measures are mysterious, as the bastardized Scandinavian femto and atto (10-15 and 10-18) had already proved. Joke aside, the need for having units as small as 10-15 and 10-24 is a serious and dramatic development. After all, a yoctomole is less than a single molecule. It makes sense only as a probability in a quantum mechanical context. It is instructive to visualize the full range of dimensions.