Reconfigurable self-assembly: from evolutive DNA assemblies to coffee-ring fortune telling and living colloidal crystals

Self-assembly is both a formidable method to organize molecular or colloidal entities into functional superstructures and a playground for the scientific endeavor on how matter organizes itself. Self-assembly is also a key feature of how life builds its components. However, compared to their living counterparts, synthetic materials made by self-assembly usually lack some characteristic properties of living systems, such as reconfigurability, adaptability, or evolution. In this presentation, I will describe different systems where such properties can emerge from self-assembled synthetic materials. First, I will show that elaborate user-defined DNA nanostructures (e.g., DNA origamis, tiles, extended nanogrids) can be obtained by spontaneous self-assembly at room temperature for the first time with a unique capability to optimize their shape, adapt, and even completely transform each time a new energy minimum appears [1,2].  I will also present a new DNA self-assembly principle that does not rely on base-pairing principles. I will show that photosensitive DNA intercalating molecules can co-assemble with DNA bases to form new extended supramolecular materials of unprecedented properties. I will describe, in particular, the formation of photoswitchable 3D crystals with unique photoreversible growth and light-gated fluorescence [3]. Finally, I will present different colloidal self-assembly processes at air-water or liquid-liquid interfaces and explore how dynamic properties can emerge from such systems. Starting from the familiar situation of a drying drop containing a colloidal suspension, we have been interested in controlling/canceling the so-called “coffee-ring effect” [4-7] or turning it into a low-cost yet powerful medical diagnostic tool [8]. In such systems, however, particles adsorb at the interface to form amorphous structures. This led us to invent a simple method in which bulk particles self-assemble at the water interface and directly crystallize there by a collective effect. Based on the use of ultralow amounts of surfactant, 2D colloidal crystals spontaneously form without any other applied force than their own weight [9]. This method allows us to crystallize a broad variety of nanometric and micrometric particles, including those made of polymers, metals, or inorganic materials, and tune the characteristics of the colloidal crystals [10]. These colloidal crystals display intense structural colors as well as, under some conditions, some remarkable dynamic properties at the air/water interface. For instance, using light, we can reversibly melt/crystallize these colloidal assemblies on command, evidencing interesting life-like properties, such as dissipative or living crystallization [11,12].

References:
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