Instantaneous attachment of an ultrahigh density of nonthiolated DNA to gold nanoparticles and its applications.

The last 16 years have witnessed the landmark development of polyvalent thiolated DNA-functionalized gold nanoparticles (AuNP's) possessing striking properties within the emerging field of nanobiotechnology. Many novel properties of this hybrid nanomaterial are attributed to the dense DNA shell. However, the question of whether nonthiolated polyvalent DNA-AuNP could be fabricated with a high DNA density and properties similar to those of its thiolated counterpart has not been explored in detail. Herein, we report that by simply tuning the pH of the DNA-AuNP mixture an ultrahigh capacity of nonthiolated DNA can be conjugated to AuNP's in a few minutes, resulting in polyvalent DNA-AuNP conjugates with cooperative melting behavior, a typical property of polyvalent thiolated DNA-functionalized AuNP's. With this method, large AuNP's (e.g., 50 nm) can be functionalized to achieve the colorimetric detection of sub-nanometer DNA. Furthermore, this fast, stable DNA loading was employed to separate AuNP's of different sizes. We propose that a large fraction of the attached DNAs are adsorbed via one or a few terminal bases to afford the high loading capacity and the ability to hybridize with the complementary DNA. This discovery not only offers a time- and cost-effective way to functionalize AuNP's with a high density of nonthiolated DNA but also provides new insights into the fundamental understanding of how DNA strands with different sequences interact with AuNP's.