The pivotal role played by DNA in biology cannot be understated. Its outstanding pairing specificity, embodied by the famous Watson-Crick mechanism, is at the core of its biological functionality. Exploiting such a specificity in synthetic applications, an idea which dates back to the seminal work of Ned Seeman in the 1980’s, provides researchers from many different fields, ranging from nanotechnology to material science, with a new, powerful tool . DNA can be used in colloidal systems as a coating agent, but also on its own to self-assemble all-DNA materials with controllable properties. In particular, short DNA strands with carefully designed sequences can self-assemble into well-defined constructs at intermediate temperature. These DNA constructs (nanostars) can, in turn, bind to each other in a controlled fashion to form higher-order structures. Recent experiments have demonstrated that DNA nanostars can be employed as experimental realisations of patchy particles [2, 3], which have shown promising properties as theoretical and numerical model systems for the synthesis of new soft materials such as empty liquids, reentrant gels and open crystals. Here we present a novel mixed numerical/theoretical approach to efficiently evaluate the phase diagram of these objects. Combining input information based on a realistic coarse-grained DNA potential with the Wertheim association theory we derive a parameter-free thermodynamic description of these systems. We apply this method to investigate the phase behaviour of single-component and mixtures of DNA nanostars with different number of sticky arms, elucidating the role of the system functionality and of salt concentration. The predicted critical parameters compare very well with existing experimental results for the available compositions . Our approach takes into account DNA-DNA interactions in a realistic fashion and therefore is very general and can be easily extended, e.g. to investigate the behaviour of all-DNA systems that incorporates DNA nanotechnology motifs such as hairpins and strand displacements.
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