Contact-free isolation of sperm and epithelial cells by laser microdissection and pressure catapulting.

With the PALM MicroBeam system, precise laser microdissection of single cells from cell smears or tissue preparations is possible. Furthermore, this system uses a contact-free and therefore contamination-free laser pressure catapulting technique in which high energy generated by a focused laser pulse catapults single dissected cells into a collecting vessel. In this study, this technique was tested for forensic purposes with smear preparations from postcoital vaginal swabs, sperm swabs, and buccal cell swabs on different types of microscopic slides. Apart from super-frosted slides, cutting and catapulting of selected cells was possible in all cases. Subsequent polymerase chain reaction was performed using the genRES MPX-2 Amplification Kit. In the case of sperm cells stained with hematoxylin and eosin, fragments larger than approximately 200 bp could not be detected. Partial genetic profiles were obtained for DNA amounts originating from only two cell equivalents. Complete profiles, however, were observed with all preparations of a minimum of 10 epithelial cells, demonstrating a potential benefit of this technique for the contamination-free forensic analysis of extremely small specimens or mixed stains.