Hyperbranched DNA clusters
Abstract
In recent years, the connection between reversible self-assembly of patchy colloidal particles, described by the Wertheim theory for associating liquids, and irreversible aggregation of chemical units, modeled by the Flory-Stockmayer (FS) theory of polyfunctional condensation, is receiving a renewed interest. Differently from the chemical case, for which equilibrium conditions are assumed (but hardly realizable in experiments), colloidal aggregation may proceed to equilibrium, allowing for a more accurate control of the theoretical FS predictions. We experimentally investigate, using Dynamic Light Scattering, the self-assembly of purposely designed DNA nanostars, able to mimic reactive monomers of type AB3, where only reactions between unlike functional groups (AB) are allowed. The clusters resulting from this aggregation process are commonly known as hyperbranched polymers. Differently from the FS theory predictions, for which an infinite percolating cluster should be present in the system when all bonds are formed, we show that a distribution of aggregates with different sizes is present. In fact, loop formation – the most significant process neglected by the FS theory – provides one more route to AB site reaction. Experimental results are supported by simulations using a coarse-grained model, which actually suggest that intra-cluster AB reactions are the preferential path to bond formation.
