Short single-strand (ss) DNA sensors that involve mono-functionalized gold nanoparticles are reported for the first time. By way of an example, the hybridization and detection of a 10 base-pair oligonucleotide (TGACTCTTAA), which relates to the pathogenicity island of vancomycin-resistant Enterococcus faecalis, has been demonstrated in the organic solvent mixture (DMF/CHCl 3/H 2O/NaCl) at sub-nanomole concentrations. The formation of the resulting double-strand (ds) DNA-AuNP complexes which involve either tail-to-tail or head-to-head alignment, are sensitive to salt (NaCl) and solvent (CHCl 3) concentrations. By UV/visible absorption measurements, it has been found that the melting temperature of the dsDNA-AuNP complexes increases with increasing salt concentrations as well as the chloroform ratio, for both tail-to-tail and head-to-head alignments. Transmission electron microscopic images of the dsDNA-AuNP complexes with mono-functionalized AuNPs reveal significant amounts of dimeric AuNP species while that of randomly functionalized AuNPs reveal an agglomerated AuNP nanostructures.
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