Flow cytometry is a means of measuring certain physical and chemical characteristics of cells or particles as they travel in suspension one by one past a sensing point. In one way flow cytometers can be considered to be specialized fluorescence microscopes. The modern flow cytometer consists of a light source, collection optics, electronics and a computer to translate signals to data. In most modern cytometers the light source of choice is a laser which emits coherent light at a specified wavelength. Scattered and emitted fluorescent light is collected by two lenses (one set in front of the light source and one set at right angles) and by a series of optics, beam splitters and filters, specific bands of fluorescence can be measured. One can measure physical characteristics such as cell size, shape and internal complexity and, of course, any cell component or function that can be detected by a fluorescent compound can be examined. So the applications of flow cytometry are numerous, and this has led to the widespread use of these instruments in the biological and medical fields.¹

The physical separation of a cell or particle of interest from a heterogeneous population is referred to as sorting. Sorting is used for a number of applications such as determining DNA content, chromosome sorting & analysis, cell sorting for cloning or PCR and apoptosis. Most cytometers are based on commercially available microscopes from leading manufacturers like Nikon, Leica or Zeiss. Many microscopes are designed for manual operation, however when modified with precision XY stages that, under computer control, step the slides or microplates through the field of view of an imaging camera, the instrument is now able to process many more samples without operator intervention. Still, whether the cells are present on glass slides or microtitre plates, the process of manual loading/unloading is tedious. Automation can free up lab personnel for long periods of time, extend runs after hours or over weekends and most important of all, protect the samples from human handling errors.

The Thermo CRS CataLyst Plate Mover is an ideal solution for further automating this process, by providing the ability to load and unload samples to the microscope stage. The articulated design of the CataLyst gives it the ability to enter tight work areas around stages and eyepieces, and the precision encoded servo motors, allow for smooth motion that ensures sample integrity. The CataLyst has a simple set up and run GUI that makes operation simple, and also provides and ActiveX control for OEM's who want to add motion to their instrument. The CataLyst uses a very robust, yet gentle servo driven gripper. This gripper can grasp microtitre plates in both portrait and landscape orientation, and sense when no plate is present. A very useful accessory from Acme Automation (http://www.acme-automation.com) called SlideRack, is a microplate shaped holder which allows for four 1x3 glass slides.

For more on cytometers and other microscope based instruments:

• Cytomation - MoFlo - High Performance Cell Sorter, Cyan - High Performance Flow Cytometer (www.cytomation.com)
• Universal Imaging Corporation - Discovery-1 - Cell Based Screening System (www.universal-imaging.com)
• Clemex -Automatic analysis of cancer cell spheroids (www.clemex.com)
• Compucyte - iCyte Automated Imaging Cytometer (www.compucyte.com)
• Diversified Scientific - CrystalScore - Automated Digital Imaging for Macromolecular
• Crystal Growth (www.dsitech.com)