Dual chemotaxis of glucose oxidase-powered nanomotors towards the concentration gradients of both glucose and proton

Inspired by the chemotaxis of natural organisms that responds to environmental stimuli, chemotactic micro-/nanomotors have been developed toward a certain chemotactic cue. However, the chemotaxis of nanomotors towards the complex environment with multiple chemical gradients is highly desired. Here, we report a glucose-powered Janus mesoporous silica nanomotor exhibiting positive, chemotactic behavior toward regions rich in glucose and low pH. The nanomotors are prepared through partially coating gold onto mesoporous silica nanoparticles and then immobilizing glucose oxidase (GOx) onto the gold patch. Due to the enzymatic catalytic decomposition, the nanomotors propelled by self-diffusiophoresis exhibit the motion behaviors dependent on the glucose concentration and pH. The translation diffusion coefficient of the nanomotors is enhanced with increasing the glucose concentration. The translation diffusion coefficient reaches the maximum value at pH 5.5 when adjusting the pH of the glucose solution. In the presence of either the concentration gradient of glucose or the gradient of pH or both, the nanomotors exhibit positive chemotactic behaviors. This result indicates that multiple chemotaxis can be involved when enzyme-powered nanomotors move towards a complex environment, which will enhance the design of nanomotors for the advanced applications such as actively targeted drug delivery.