Towards self-replicating materials of DNA-functionalized colloids

We report the first results of ongoing research that involves the creation of a new class of non-biological materials designed to self-replicate and, as a result, to grow exponentially. We propose a system design that exploits the strong specificity and thermal reversibility of the interactions between colloidal particles functionalized with complementary single-stranded DNA 'sticky ends'. Here, we experimentally test the fundamentals of the different steps that constitute the self-replication scheme. First of all, we quantitatively study the equilibrium and kinetic aspects of the aggregation-dissociation behavior of the particles. We find that the dissociation transition is very sharp (similar to 1 degrees C) and that it occurs at unexpectedly low temperatures, with the dissociation temperature shifting further down when the fraction of sticky ends becomes smaller. The sharpness of the transition and its sensitivity to the sticky end fraction are important control parameters in our self-replication scheme. We further find that for our present purposes it is best to use a DNA construct with a double-stranded backbone, as this largely prevents unwanted hybridization events, such as secondary structure formation. The latter is seen to lead to peculiar aggregation kinetics, due to a competition between inter- and intra-particle hybridization. Finally, we show how one can obtain dual recognition at different temperatures by functionalizing a single particle species with two distinct DNA sequences and we demonstrate the formation of permanent bonds, using the chemical intercalator psoralen and long-wavelength UV exposure.