An increasing number of diseases are being associated with specific chromosomal abnormalities, such as translocations, inversions, and deletions. Selection of individual chromosome G-bands allows preparation of clinical diagnostic probes for chromosomal analysis and identification of these abnormalities. Presently, the desired chromosome band is removed by scraping it off a slide with a micropipette attached to a hydraulic manipulator while monitoring the process using an inverted microscope equipped with a 100X objective lens. The needle, oriented approximately perpendicularly to the chromosome of interest both demarcates the desired material from the rest of the chromosome, and removes the material for subsequent processing. In a new system we have developed, a UV (390nm) laser is used to very sharply demarcate the material to be acquired and ablate the immediate surrounding material. The desired material is then removed by a micropipette moved by a specially developed mechanism under computer control. It is hoped that by relying on the laser to trim away the undesired material, there will be less extraneous material than when the shearing action of the micropipette is used to separate out the sample from the remaining material. In addition, by sensing the needle tip position with the objective lens focus position and a video image, as well as employing a computer to determine the motions of a mechanism, the manual dexterity requirements on the operator will be greatly reduced, thus allowing the technique to be more widely used. The new system is still being evaluated. It appears that static electricity effects sometimes interefere with the deposition of the scraped material into its collection cuvette. Various means of eliminating the effect are being explored.
