Hybridization studies on 60-micron PEG-polystyrene beads. Images show DNA-conjugated beads with buffer alone (A,B); beads after hybridization with yyDNA (5′-dyyCCTTCTCC) and washing (C,D); and digitally subtracted difference images (E,F). A,C,E: scrambled control DNA sequence 5′- GAGAGAGA on beads; B,D,F: complementary sequence (5′- GGAGAAGG) on beads. Hybridization and wash buffer contained 100 mM NaCl, 10 mM MgCl2, 10 mM Na•PIPES (pH 7.0), 25 °C. Increased fluorescence with complementary beads vs. scrambled controls (compare D to C and F to E) is consistent with sequence-selective hybridization of yyDNA. Anomalous dark and light spots in E (2 spots) and F (4 spots) arose from beads that moved between background and hybridization images.