A gold nanoparticle densely modified with DNA (DNA 'AuNP), which integrates the ability of molecular recognition with plasmonic properties, is a well-established platform in nanobiotechnology. Both in analytical science and materials science, DNA 'AuNP assemblies crosslinked by Watson-Crick base pairing have gained great popularity. Yet the finding of non-crosslinking aggregation of DNA 'AuNPs has brought us to another fascinating side of this material. Upon hybridization with the complementary DNA, the DNA 'AuNPs undergo a dramatic decrease in colloidal stability accompanied with a distinct color change due to blunt-end stacking interactions. When hybridized to the terminal-mismatched DNA, the DNA 'AuNPs stay dispersed even at high ionic strength by virtue of fraying motion of the outmost unpaired nucleobases. This distinct colloidal phenomenon provides a colorimetric approach to discriminate single-nucleotide polymorphisms. Furthermore, by region-specific arrangement of single-base pairing/unpairing at the outmost surface of the DNA layer, gold nanorods can spontaneously evolve to assemble in an orientation-controlled fashion, promising applications in fabrication of various nanodevices.