Light controlled crystallization of DNA coated particles

DNA coatings have been proposed and successfully applied as a versatile tool for programming the self-assembly of micrometer size particles into numerous crystalline structures. The DNA-mediated interaction is highly temperature dependent. For given buffer conditions, a set of complementary DNA-coated particles present a melting temperature T_melt that marks the transition between aggregated and melted states. Without a change of environment, one has no further control over T_melt and a local control of the interaction is challenging.
Here we present a strategy that uses the combination of DNA coatings and an azobenzene photo-switch to access fine control of the interaction between particles, independently from temperature. Azobenzenes reversibly switch between trans and cis conformations, an exposure to UV or blue light shifts the population towards the cis or trans respectively. Once attached to the backbone of a DNA sticky-end, the flat trans form can intercalate in the double helix and stabilize the duplex. On the contrary the kinked cis azobenzene disrupts the hybridization. We harvest this molecular behavior to modulate the melting temperature of DNA-coated particles, pattern their melting or aggregation, correct defects on the crystals and switch between crystal structures.