Light-induced selective speed alteration of magnetically rolled semiconductor particles.

Microrobot teams or swarms are promising candidates for many applications, such as micromanipulation, microsurgery, or targeted drug delivery. However, attaining individual control of the microrobots, which is a critical component to many of their applications, remains a significant technical challenge. We introduce a method to control the magnetic rolling speed of hematite semiconductor particles using localized UV light, attributed to light-induced changes in particle-substrate friction. Simulations and theoretical models support our experimental observations, showing how particle-substrate separation influences speed. Additionally, we demonstrate fixed patterning of microparticles via selective UV illumination at lower pH, demonstrating selective immobilization of microrobots, a conceptual step toward applications such as targeted drug delivery or patterned cell stimulation in future studies. Therefore, this work provides a novel approach for independent control of microrobot systems by modulating particle-substrate interactions with light.