You can try AlkPhos Direct Labelling with GE RPN3690 kit and CDP-Star Reference: //www.ncbi.nlm.nih.gov/pubmed/21375737 citation: Twenty-nine colonies were identified and expanded, and colonies were subsequently genotyped by non-radioactive Southern blot (GE RPN3690 kit with CDP-Star) with a 500-bp probe 5’ to the targeting vector and following the manufacturer’s directions for labeling, Manufacturer’s Protocol link: HTTPS//www.gelifesciences.com/gehcls_images/GELS/Related%20Content/Files/ 1314716762536/litdoc18113911_20110830173835.pdf