Chemical herding: Steering colloidal particles using chemical reactions

Dynamically programmable colloidal materials (DPCMs) are an emerging class of materials that change their structure based on external stimuli. With the correct programming, DPCMs could be influenced to organize into arbitrary structures currently unattainable, with applications in photonics, tissue engineering, and nanorobotics. However, realizing such applications requires spatiotemporal control of colloids to a combined precision and scale that is currently unattainable. We have developed a new method for using chemical reactions to multiply the effects of existing top-down colloidal manipulation methods to arrange large numbers of colloids with single particle precision, which we refer to as chemical herding. Using simulation-based methods, we show that if a set of chemically active colloids (herders) can be steered using external forces (i.e. electrophoretic, dielectrophoretic, magnetic, or optical forces), then a larger set of colloids (followers) that move in response to the chemical gradients produced by the herders can be steered to target locations. Based on our theoretical results and simulations, we conclude that chemical herding is a viable method for multiplying the effects of existing colloidal manipulation methods to create useful structures and materials.