Stimuli-responsive self-regulating assembly of chiral colloids for robust size and shape control.

Most synthetic self-assemblies grow indefinitely into size-unlimited structures, whereas some biological self-assemblies autonomously regulate their size and shape. One mechanism of such self-regulation arises from the chirality of building blocks, inducing their mutual twisting that is incompatible with their long-range ordered packing and thus halts the assembly's growth at a certain stage. This self-regulation occurs robustly in thermodynamic equilibrium rather than kinetic trapping, and therefore is attractive yet elusive. Until now, studies of self-regulating assemblies have focused on non-responsive systems, whose equilibrium point and corresponding size and shape are hardly changeable. Here, we demonstrate a stimuli-responsive, self-regulating assembly. This assembly consists of chiral and magnetically orientable nanorods, where the effective chirality can be changed by balancing chirality-induced twisting and magnet-induced flattening between nanorods. Consequently, the strength of self-regulation in the assembly is modulable by magnetic field intensity, allowing robust, tunable, and reversible control of its size and shape. Our strategy would provide more biomimetic materials with precision and responsiveness.