(111a) Specific and Non-Specific Molecular Control of Catalytic Active Janus Particles

Active colloidal particles experience a superposition of stochastic and deterministic motion that often results from local cues in the environment. These systems serve as useful analogs to micrometer scale entities that propel in nature such as a flagella-containing bacterium. Local crowding because of a neighboring boundary or particle will induce conservative and non-conservative interactions that will affect the particle’s motion. Further, these interfacial phenomena offer an avenue to control the propulsion of active Janus particles. Herein, we describe experiments in which we measured the influence of both specific and non-specific molecular interactions on the active motion of 5 µm catalytic active Janus particles at infinitely and moderately dilute conditions. The non-specific interactions were controlled with non-reactive polyethylene glycol (PEG), while the specific interactions were controlled with a protein designed to bind with the catalytic platinum cap. We found that at infinitely dilute conditions, propulsion speed was reduced upon the addition of PEG. Low concentrations of PEG tended to increase clustering at moderate particle concentrations, while high concentrations of PEG reduced cluster formation. Subsequent work with proteins with a platinum binding tag showed that the addition of a specific binding protein reduced propulsion speed in a qualitatively similar way to PEG. These data support the hypothesis that propulsion of active Janus particles can be altered via addition of solutes that interact in both specific and non-specific ways with the particle.