Protocol describes a high sensitivity indirect detection procedure for DIG-labeled hybridization probes. The procedure uses the components of the HNPP Fluorescent Detection Set to form a fluorescent precipitate of HNPP (2-hydroxy-3-naphthoic acid-2’-phenylanilide phosphate) and Fast Red TR at the site of hybridization. This procedure can be used to detect single copy sequences as small as 1 kb on human metaphase chromosomes.
