Photoactivated immobilization of single-stranded DNAs on a psoralen-functionalized surface under low pH conditions

Single stranded DNA was photo-patterned on a psoralen-functionalized surface and conjugated with a psoralen-modified enzyme. Photoreactions between the single-stranded DNA and psoralen-functionalized materials were found to be significantaly influenced by pH, showing high efficientcy only under acidic conditions. Specifically, the photopattering of single-stranded DNA probes, such as polythymine, polyadenine, polycytosine, and polyguanine, on a psoralen-functionalized amino-dextran surface under various pH conditions (pH 3.36–8.80) showed that the polythymine probes had the highest immobilization efficiency at pH 3.36. The effect of pH was further confirmed by photopatterning the single-stranded DNA probes using the photomask. While almost no pattern was observed on the psoralen surface at pHs greater than 5.5, much more visible patterns were observed as the pH was decreased below 5.5. As a result of the irradiation of polyT 15 and polyA 15 -labeled DNA probes, the photopatterns formed by the irradiation of polythymine probes were found to be associated with the cross-linking between the thymine and the psoralen moieties. Finally, additional studies showed that psoralen could be used as the reactive center in the photo-induced cross-linking reaction between DNA and the model protein, horseradish peroxidase (HRP).