BioChip J. (2012) 6(2): 174-183 DOI 10.1007/s13206-012-6210-8 Abstract Single stranded DNA was photo-pattern- ed on a psoralen-functionalized surface and conjugat- ed with a psoralen-modified enzyme. Photoreactions between the single-stranded DNA and psoralen-func- tionalized materials were found to be significantaly influenced by pH, showing high efficientcy only under acidic conditions. Specifically, the photopatter- ing of single-stranded DNA probes, such as polythy- mine, 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 immo- bilization efficiency at pH 3.36. The effect of pH was further confirmed by photopatterning the single-strand- ed 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 ob- served 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 irra- diation of polythymine probes were found to be asso- ciated with the cross-linking between the thymine and the psoralen moieties. Finally, additional studies show- ed 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). Keywords: DNA immobilization, Psoralen, pH effect, DNA photopatterning, DNA-protein photocrosslinking Introduction DNA photopatterning has been actively studied be- cause it is a useful method for the immobilization and speicific positioning of DNA molecules on various surfaces, such as in microfludic channels. In addition, this micropatterning technology has been utilized in the construction of arrays containing micrometer- sized spots. For example, thiol-modified DNA probes have been employed in the UV irradiation induced immobilization process with trifluoroacetamide pro- tected 10-aminodec-1-ene on a gallium nitride thin film containing an Au substrate 1 . Moreover, various substrates that were spin-coated with acryloyl-func- tionalized polymers containing terminal epoxy groups have been used to affix amine-modified DNA in a specific pattern through the UV promoted photocross- linkng 2 . Amine-modified DNAs have also been photo- immobilized on compact disc surfaces of polycarbo- nate substrates located in microfluidic channels 3 . In addition to acryloyl-functionalized polymers, inves- tigations in this area have focused on diazoketo-func- tionalized polymers that are employed as photoche- mical cross-linkers in the immobilization of the amine- modified DNA 4 . Furthermore, the DNA immobiliza- tion process generally involves initial photopatterning of a gallium nitride thin film with trifluoroacetamide- Original Research Photoactivated immobilization of single-stranded DNAs on a psoralen-functionalized surface under low pH conditions Junhyoung Ahn 1,2,† , Ju Young Byun 3,4,† , Yong-Beom Shin 1,2 & Min-Gon Kim 4,5 Received: 9 March 2012 / Accepted: 26 April 2012 / Published online: 20 June 2012 � The Korean BioChip Society and Springer 2012 1 Nanobiotechnology Major, School of Engineering, University of Science & Technology (UST), Daejeon 305-806, Korea 2 Immune Therapy Research Center, Korea Research Institute of Bioscience & Biotechnology (KRIBB), Daejeon 305-806, Korea 3 Department of Fine Chemical Engineering & Applied Chemistry, Chungnam National University, Daejeon 305-764, Korea 4 Advanced Photonics Reseach Institue, Gwangju Institute of Science & Technology, Gwangju 500-712, Kroea 5 Department of Photonics & Applied Physics, Gwangju 500-712, Kroea † These authors contributed equally to this work. Correspondence and requests for materials should be addressed to M.-G. Kim ( mkim@gist.ac.kr)