By: Erika Eiser
From: University of Cambridge
At: Faculdade de Ciências, Ed. C1, 1.3.14
I will introduce a new binary system made of DNA-functionalized, filamentous fd-viruses of ∼880 nm length with an aspect ratio of ∼100, and 50 nm gold nanoparticles (gold- NPs) coated with the complementary DNA strands. When quenching mixtures below the melt temperature Tm, at which the attraction is switched on, we observe aggregation. Conversely, above Tm the system melts into a homogenous particulate `gas’. I will present the aggregation behavior of three different gold-NP to virus ratios and compare them to a gel made solely of gold-NPs. In particular, we have investigated the aggregate structures as a function of cooling rate and determine how they evolve as function of time for given quench depths, employing fluorescence microscopy. Structural information was extracted in the form of an effective structure factor and chord length distributions. Rapid cooling rates lead to open aggregates, while slower controlled cooling rates closer to equilibrium DNA hybridization lead to more finestranded gels. Despite the different structures we find that for both cooling rates the quench into the two-phase region leads to initial spinodal decomposition, which becomes arrested. Surprisingly, although the fine-stranded gel is disordered, the overall structure and the corresponding length scale distributions in the system are remarkably reproducible. Such highly porous systems can be developed into new functional materials.