Chemical logic gates on active colloids

Synthetic active colloidal systems are being studied extensively because of the diverse and often unusual phenomena these nonequilibrium systems manifest, and their potential applications in fields ranging from biology to material science. Recent studies have shown that active colloidal motors that use enzymatic reactions for propulsion hold special promise for applications that require motors to carry out active sensing tasks in complicated biomedical environments. In such applications it would be desirable to have active colloids with some capability of computation so that they could act autonomously to sense their surroundings and alter their own dynamics to perform specific tasks. Here we describe how small chemical networks that make use of enzymatic chemical reactions on the colloid surface can be used to construct motor-based chemical logic gates. Some basic features of coupled enzymatic reactions that are responsible for propulsion and underlie the construction and function of chemical gates are described using continuum theory and molecular simulation. Examples are given that show how colloids with specific chemical logic gates can perform simple sensing tasks. Due to the diverse functions of different enzyme gates, operating alone or in circuits, the work presented here supports the suggestion that synthetic motors using such gates could be designed to operate in an autonomous way in order to complete complicated tasks.