Structural study on gold nanoparticle functionalized with DNA and its non-cross-linking aggregation.

Hybridization of DNA tethered on colloidal nanoparticles with fully matched complementary one induces the aggregation of the particles in a non-cross-linking configuration. Here, we performed a structural study on DNA-functionalized gold nanoparticle and its non-cross-linking aggregation mainly using synchrotron radiation small-angle X-ray scattering. To understand the non-cross-linking aggregation, the nanoparticles with various DNA lengths and core sizes were used. In the aggregation, the surface distance between the gold nanoparticles increased with the length of DNA duplex, although the increment of the distance per base pair was not constant and showed the tendency to become small with increasing DNA length, meaning the interdigitation of DNA layers. The aggregation was also found to occur between the identical cores, without being affected by tethered DNA. Furthermore, it was proved that the relative increase in DNA length to core size leads to the increase in colloidal stability. Even the nanoparticles with full-matched DNA duplex were dispersed stably. These facts suggested that van der Waals interaction between core particles rather than end-to-end stacking between DNA duplexes is a dominant attractive interaction. The steric repulsion force arising from entropic loss of thermal fluctuation of DNA molecules might be a key factor to characterize the non-cross-linking aggregation.