Biomimetic Chemotactic Motion of Self-Assembling Doublet Microrobots

Bio-hybrid robotics at the microscale promises to advance intelligent systems in biomedical devices, environmental monitoring, and soft robotics by emulating complex behaviors found in living entities, such as chemotaxis. Here, the shape-dependent chemotaxis of doublet microswimmers, with various morphologies that exhibit autonomous movement in hydrogen peroxide (H2O2) gradients without the need for complex material preparation, are reported. These microswimmers consist of a double-sphere structure composed of one colloid with a catalytic silver (Ag) surface and a second one with a passive silica surface. Catalytic decomposition of H2O2 on the Ag surface enables propulsion with the Ag side forward. In the presence of an H2O2 gradient, differential reaction rates across the Ag particle induce a torque that continuously reorients the microswimmers toward higher H2O2 concentrations, resulting in positive chemotaxis. The findings highlight the crucial role of particle morphology in chemotactic behavior and provide insights for designing artificial microswimmers with enhanced navigation capabilities in chemical gradients.