Over a number of years, I have found it desirable to firmly hold a sample in the SEM without the contamination problems (or sample creep) associated with carbon tape. My approach to this has been to make a small vice suitable for gripping the sample which will still fit into a standard pin-mount style sample stage. I have made a number of specimen holders over the last few years, at rock-bottom prices.

In a pyrotechnic composition, the morphology (size, shape and surface features) of individual particles in the mixture influences both burn rate and the ease of ignition of the composition. Collectively, the larger, more rounded and smoother the particles, the lower the burn rate and the more difficult it is to ignite the composition. However, the purpose of the current investigation was only to catalogue some particle morphologies that may be useful in forensic identification of unconsumed or residual pyrotechnic evidence. In this study, potassium nitrate was chosen because of its common use in pyrotechnics and because of its similarity with other frequently used pyrotechnic oxidizers.

All samples were prepared for scanning electron microscopy using a double-sided adhesive carbon disk applied to an aluminum post. Particles were mounted to the carbon disk and sputter coated with gold.

Fluorescence imaging of brains from older animals, particularly primates, can be hindered by the presence of lipofuscin, a strongly fluorescent pigment that accumulates with age, primarily in neuronal cells. Lipofuscin has a broad emission spectrum that overlaps emission of most fluorescent labels, is present throughout the brain and other tissues, and is very hard to quench chemically (Schnella et at.. Journal of Histochemistry and Cytochemistry, Vol. 47, 719-730, 1999). A more convenient way to eliminate lipofuscin from fluorescence images is the use image arithmetic to subtract its signal. This method takes advantage of lipofuscin's broad emission spectrum that makes it appear in all fluorescence channels.

The identification of marijuana (Cannabis sativa) is a routine analysis in many forensic laboratories. An important part of this analysis is the identification of trichomes, commonly called cystolithic hairs, on plant particles. These hairs contain calcium carbonate, The very word cystolithic derives from this fact, coming from the Greek kustis and lithos meaning, “bag of stones”.

Trichomes are not unique to marijuana but are common on many species of plants. Thus, the mere presence of trichomes on a leaf surface is not sufficient. A required step in the identification of marijuana is the microscopical characterization of the cystoiithic hairs present on the leaf fragments.

Section thickness can be measured by placing beads of some kind on the top and bottom surfaces of the section. This is then a simple parallax problem.

Imagine the specimen in cross section. If there are two particles, one vertically above the other they are separated by the film thickness T. Tilt the film through an angle A and in plan view the particles will separate by a distance D. This can also be extended to account for two particles not vertically above each other but I'll stick to the easy case for the explanation.

Take two negatives one at zero tilt and one at tilt of A and measure the separation D. The thickness can be calculated by T=D/sinA.

The direction of the tilt axis must be known for the measurements and it is easy to see that the larger the tiit angle and the more accurately the separation is measured, the more accurate the measurement will be. Tilt at both positive and negative angles to get a more accurate result.

Since the discovery of nerve growth factor, it has been thought that neurotrophic factors are released or secreted from target cells. However, more recently it has been suggested that a specific neurotrophic factor known as brain-derived neurotrophic factor (BDNF) may reach target cells directly from presynaptic axons. It has not been known how these molecules get from the neuron in which they are produced to the target cells. Keigo Kohara, Akihiko Kitamura, Mieko Morishima, and Tadaharu Tsumoto have demonstrated that BDNF is transported anterogradely from presynaptic neurons to target neurons.

It is most important that any test specimens used to audit an instrument are from a traceable source and are certified by a recognised body.

Traditional methods for the evaluation of resolution in the scanning electron microscope rely upon a high-density particle upon a low-density substrate, the most popular method being evaporated gold on a carbon substrate. Although most manufacturers use this method, it is subject to abuse as there is no inbuilt magnification standard and therefore the evaluation of the image may only be made through measurement. To simply judge the specimen by appearance as most scientists do, could lead to a misleading result.

An ideal specimen for the evaluation of scanning electron microscope performance is dried polystyrene latex sputter coated with gold, or gold palladium for the evaluation of higher performance (e.g., field emission instruments) (Figure1). The specimen requires very pure polystyrene latex that is allowed to settle and dry down over a period of time sufficient for it to form a solid block. The block is fixed to a specimen stub with silver Dag and the adhesive allowed to dry.

Recently there was an exchange on the Confocal Listserver about the proper method for cleaning objective lenses. Some suggestions were useful and were some fraught with danger. This article is adapted from my reply to the list.

There are only three hard and fast rules about lens cleaning:

1. 1) Never “dry” clean a lens.

2. 2) Use a solvent or dispersant that is likely to remove whatever is on the lens.

3. 3) Use the best quality lens tissue available.

The most likely source of damage to glass surfaces and fine optical coatings is abrasion. The particles that cause the abrasion are the particles on the objective lens surface and the particles in whatever is used to wipe the lens.