DNA binding and hybridization on gold and derivatized surfaces
The binding of various single- and double-stranded DNAs onto gold and derivatized gold surfaces, and their hybridization with complementary DNA species, have been investigated using a quartz crystal microbalance (QCM) and surface plasmon resonance (SPR). The DNA species employed were a 21-mer oligonucleotide (Mbo21), several double-stranded plasmid DNAs (7.2 kilobases) modified by incorporation of α-phosphothio-nucleotides into the ends of the linearized plasmid DNA (pPS-Sx, where x represents the number of α-phosphothio-nucleotides), and a 30-mer oligonucleotide having a mercaptohexyl group at the 5′-phosphate end (BS1-SH). Both QCM and SPR data reveal that unmodified DNA does not spontaneously adsorb onto underivatized gold surfaces from aqueous solutions. Modification of the gold surface through the attachment of an ionizable thiol compound, 2-dimethylaminoethanethiol hydrochloride (DMAET), allows DNA to adsorb through electrostatic interactions. SPR measurements confirm the presence of Mbo21 DNA on the DMAET-modified gold surface. Immobilized Mbo21, however, does not undergo hybridization. QCM and SPR data suggest that pPS-S4, pPS-S50 and BS1-SH DNA all assume a flat orientation on gold. No hybridization of single-stranded DNA to gold-immobilized pPS-S4 and pPS-S50 could be detected. In contrast 30-mer DNA binding from solution to the complement BS1-SH immobilized on gold reveals hybridization of the DNA strands.
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