Self-adaptive enzyme-powered micromotors with switchable propulsion mechanism and motion directionality

Abstract

Switchable chemotaxis is vital for motile microorganisms seeking benefits or to avoid harm. Inspired by nature, and for the first time, we demonstrate an artificial enzyme-powered micromotor that can autonomously regulate the propulsion mechanism, as well as motion directionality, by solely sensing the change of fuel concentration (Cf) in its surroundings. The as-designed micromotors have a pot-like microstructure with ureases immobilized on the inner surface. With the confined effect of the pot-like microstructure and unique features of the urease catalytic reaction, the molecular products are further reacted into ions, and their propulsion mechanism can be reversibly adjusted between ionic diffusiophoresis and microbubble recoils when Cf changes. Consequently, the as-developed micromotors under magnetic field are able to self-turn back if the local Cf differs greatly in their surroundings, indicating the achievement of positive and negative chemotaxis by sensing local Cf. Meanwhile, the micromotors also show highly enhanced migration speed by microbubble ejection, up to 60 μm/s, around 30 body lengths per second at physiological urea concentrations. Furthermore, they have an outer surface of mesoporous silica which is easily functionalized for applications such as stimuli-responsive delivery-associated therapies. This work will promote “smart” artificial micro/nanomotors for in vivo biomedical applications.