The chemisorption of oligodeoxynucleotide phosphorothioate (s-oligo) is reported. A series of s-oligo DNAs was designed for use as capture probe DNA molecules. The s-oligo DNAs consist of the K-ras gene (5'-GGA GCT GGT GGC-3') and a dodecamer deoxyriboadenosine, both of which lie on either side of an s-oligo DNA sequence. By primarily focusing on the capture probe DNA having five-successive s-oligo sequences, e37, the immobilization chemistry of e37 was examined; atomic force microscopy achieved the direct visualization of individual molecules on Au(111) substrates, while a series of surface analyses, including IR, ellipsometry, and microgravimetry, showed that the s-oligo functional groups played a pivotal role in the surface-adlayer through the gold-thiol interaction. Interestingly, the amount of immobilization showed a definite relationship with the number of s-oligo linkages introduced, which should be important to regulate the concentration of the capture probe DNA molecules on the surface. Some preliminary studies using ferrocene-modified complementary sequences indicated that electrochemical labeling and readouts were possible.
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