Light-up Hoechst-DNA aptamer pair: generation of an aptamer-selective fluorophore from a conventional DNA-staining dye.

We have designed a strategy to generate a light-up fluorophore-aptamer pair based on a down-modification of a conventional DNA-staining dye to suppress its affinity to the original dsDNA targets, followed by reselection of aptamers that would bind to the modified dye. Following this line, we prepared a micropolarity-sensitive Hoechst derivative possessing two tBu groups with low affinity to the usual AT-rich dsDNA targets. DNA aptamers selected in vitro from a random pool worked as triggers to enhance the fluorescence of an otherwise nonfluorescent Hoechst derivative, and the shortened 25-mer sequence showed remarkable enhancement (light-up). The 25-mer sequence was split into binary aptamer probes, thus enabling us to detect a target nucleic acid sequence with a single-nucleotide resolution by use of unmodified DNA as a probe.