Swarming magnetic photonic-crystal microrobots with on-the-fly visual pH detection and self-regulated drug delivery

Swarming magnetic micro/nanorobots hold great promise for biomedical applications, but at present suffer from inferior capabilities to perceive and respond to chemical signals in local microenvironments. Here we demonstrate swarming magnetic photonic-crystal microrobots (PC-bots) capable of spontaneously performing on-the-fly visual pH detection and self-regulated drug delivery by perceiving local pH changes. The magnetic PC-bots consist of pH-responsive hydrogel microspheres with encapsulated one-dimensional periodic assemblies of Fe 3 O 4 nanoparticles. By programming external rotating magnetic fields, they can self-organize into large swarms with much-enhanced collective velocity to actively find targets while shining bright “blinking” structural colors. When approaching the target with abnormal pH conditions (e.g., an ulcerated superficial tumor lesion), the PC-bots can visualize local pH changes on the fly via pH-responsive structural colors, and realize self-regulated release of the loaded drugs by recognizing local pH. This work facilitates the development of intelligent micro/nanorobots for active “motile-targeting” tumor diagnosis and treatment.