The ability to attach fluorescent molecules onto proteins has allowed specific localization of these proteins within living cells. The traditional approach has been to purify the protein of interest then attach a fluorescent (or another useful tag) molecule in vitro, then somehow introduce the labeled protein into the cell. Whereas this and related techniques have been very useful, there are limitations because each of these three steps is often difficult. Wouldn't it be great if we had a “lock and key” system whereby a protein of interest could be modified to be a specific “lock” and a small tsggable molecule (the “key“) could diffuse into the cell and plug specifically into the lock? Albert Griffin, Stephen Adams, and Roger Tsien have developed such a system

Detection of characteristic x-rays is a fascinating and challenging subject. From its early beginnings with gas proportional counters it has evolved, like many branches of technology, into the use of a variety of semiconductors.

The lithium compensated silicon detector [Si(Li)] has been the predominant measuring tool over the last two decades, in the last five years, increasing numbers of high purity germanium detectors (HPG) have appeared and more recently a plethora of new materials and concepts are seeing a successful introduction. Among these newer materials are compound semiconductors like mercuric iodide, cadmium telluride, cadmium zinc telluride, gallium arsenide, lead iodide, indium phosphide and diamond. Among the new concepts are Bolometers, Transition Edge Detectors, Drift Detectors, PIN Diodes, CCD arrays and PN CCD arrays.

With today's current wave of quality consciousness, our quality control people tell us we MUST calibrate our instruments using standards that are traceable to the national laboratories (NIST - National Institute of Standards and Technology in the U.S.,. NPL - National Physical Laboratory in the UK, and others). But, is it really magnification that should be calibrated?

While recently walking around the exhibit floor at the Microscopy & Micrcanalysis ‘98 Conference, I noticed the large SEM image display screens that now present our highly magnified specimens. Almost all vividly show a micron (using SI units this should be a “micrometer”) marker as well as the magnification. No doubt the accuracy is within the ± 3% that is commonly quoted by the manufacturers.

The scale of features that control the physical properties of engineered materials is ever decreasing. We can investigate the structure of these materials using several techniques. The techniques are usually selected based on the feature size of interest. Typical scales are the millimeter or optical scale, the micron or microscopic scale, and the nanometer or atomic scale. As the feature size decreases, the capabilities of the technique must increase.

Typical features that require at least microscopic characterization include particles in super alloys, grain misorientations in high temperature superconductors and thin films, inclusions in steels, reaction products in gas chambers.

The scintillator Is a part of the electron collection system in most SEMs and other types of electron imaging systems. Without a properly functioning scintillator, images may be noisy, weak, or exhibit other signs of degradation.

There are three types of scintillators generally used in the SEM: organic/polymeric, phosphor powder, and crystalline (single or poly).

Plastic scintillators are currently used less frequently, mainly because they are subject to radiation damage (i.e., short lifetime). This type of scintillator has the shortest decay time (~2.2 - 5 ns) and very low noise. We still have many customers who prefer this type of scintillator even though they have to change it more frequently (∼2 - 6 month lifetime with average use is our experience).

Microscopists have special challenges when presenting image data to audiences, Issues such as image size, resolution, and labeling are related to the format of the presented image. Contact prints, transparencies, 35 mm film, and projected video of digital images are some of the output options possible for microscopy presentation. This brings us to a question which Jonathan Krupp of the University of California, Santa Cruz, recently posed to the Microscopy listserver;

Small particle contamination analysis requires consideration of secondary contamination of our sampie. Protection of such samples is very important. The procedure for sampling with freshly pulled lengths of clear 3M Magic™ tape is a favorite procedure among forensic microscopists. The tape must be immediately pressed onto a clean surface; usually, a clean microscope slide. There it is protected from further contamination.

Microscopical study and identification is usually possible utilizing the tape backing as a coverslip. Its thickness Is about 56 μm, one-third of the recommended 170 μm, but quite adequate for objectives 4-20X, If you feel persnickety, you can use two thicknesses of the tape, a second one over the sampling tape, This will give you optimum images for 4-40X objectives. Three thicknesses of tape, at 168 μm, is very close to the recommended thickness of 170 μm for any or all objectives.

Project MICRO (Microscopy in Curriculum - Research Outreach) is the Microscopy Society of America's educational outreach program for middle schools. The idea began in 1993, but has taken a lot of time and effort to implement. MSA's early decision to collaborate with experienced science educators at the Lawrence Hall of Science (LHS) of the University of California at Berkeley was a wise one as their educational materials have a well-earned national reputation for excellence. The first phase of MICRO has just been completed, with the publication of a LHS teacher's manual that will support the MSA/MICRO effort to get microscopist-volunteers into classrooms nationwide.

Three commercially available vacuum samplers (also known as microvacuum samplers or microvacs) were examined for compliance with the Standard ASTM Methods for asbestos in settled dust. The American Society for Testing and Materials (ASTM) Standard Test Method (D5755-95) for Microvacuum Sampling and Indirect Analysis of Dust by Transmission Electron Microscopy for Asbestos Structure Number Concentration and the similar Method (D5756-95) for mass require that a sample be collected by vacuuming a known surface area with a standard 25 or 37 mm air sampling cassette using a plastic tube that is attached to the inlet orifice which acts as a nozzle.

Low vacuum and environmental SEMs have become commonplace in many labs for many applications. With the rise in popularity of these instruments comes the need to understand their capabilities and limitations. An article I wrote in this publication in August 1997 summarized the issue of beam scatter in the low vacuum SEM, In this first of a series of three articles, I will go into more detail and give more examples on the phenomena of beam scatter in the low vacuum SEM.

The problem of beam scatter in the low vacuum SEM chamber is well known. Electrons from the primary beam interact with gas molecules in the SEM chamber, scatter, and hit the sample surface some distance away from the primary beam. The result is a “skirt” of electrons much wider than the primary beam. The amount of scatter depends on four variables: chamber pressure, working distance, accelerating voltage, and gas type. I will discuss the first three in this paper. The effect of gas type will be addressed in the next issue.