Abstract: Detection of in situ hybridization to human metaphase chromosomes provides important information about gene mappings and about analysis of chromosomal disorders. We applied atomic force microscopy (AFM) to the detection of in situ hybridization to get better resolution as compared to light microscopy. Chromosomes were spread over a glass substrate and hybridized with DNA probes labeled with biotin or digoxigenin. The hybridized probes were reacted with streptavidin or anti-digoxigenin antibody, both of which were conjugated with 5-nm gold colloidal particles. We missed direct detection of the conjugated gold colloidal particles by micro-meter scale AFM scanning , but obtained clear topographic difference between the site of hybridization and the chromosome arm with the help of silver enhancement. We thus clearly detected the in situ hybridization using chromosome painting probes, alpha satellite probes, and locus specific gene probes by AFM. The in situ hybridization to DNA fiber was also detected by AFM. The detection of in situ hybridization by AFM has advantages over fluorescence in situ hybridization: no reduction of signal intensity under light irradiation. Application of AFM to the detection of in situ hybridization will be a useful method to analyze chromosomes. !22
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