Collective Dynamics of Urease-Based Nanomotors in a Chemical Gradient

Gradients are widespread in nature, including within the human body, making the study of nanomotors' collective dynamics in gradients crucial to advancing biomedical applications and deepening the understanding of natural active matters. However, the comprehensive understanding of nanomotors' collective dynamics under gradients remains underexplored, particularly. This study employs urease-based nanomotors (UrNMs) as a model system to explore their collective dynamics within a urea gradient, revealing three fundamental principles that govern their behavior: density-driven convection, UrNMs' response to the urea gradient, and a coupling effect between UrNMs and their environment. Initially, migration is dominated by convection-induced motion arising from the steep gradient. As convection gradually diminishes, UrNMs' positive response to the urea gradient becomes the dominant factor governing their migration. Notably, the coupling effect between nanomotors and the gel, plays a crucial role in the migration process. This coupling effect arises from hydrogen bonding between product anions and the gel, which generates ionic gradients. The dominant influence of electric force is validated by pH-controlled experiments. These insights advance the fundamental understanding of gradient-responsive nanomotor behavior and offer inspiration for the design of intelligent, environment-sensitive active systems.