Motion-based pH sensing using spindle-like micromotors

In this study, we report a spindle-like micromotor. This device, which is fabricated using a one-step electrospinning method, consists of biodegradable polycaprolactone and an anionic surfactant. Intriguingly, not only can the resulting micromotor move autonomously on the surface of water for a long period of time (~40 min) due to the Marangoni effect, but it also exhibits a pH sensing behavior due to variations in the surface tension caused by the release of surfactant under different pH conditions. More interestingly, we reveal that the motion-based pH sensing property is size-dependent, with smaller structures exhibiting a higher sensitivity. In addition, since polycaprolactone is a biodegradable material, the micromotor described in this study can be easily degraded in solution. Hence, features such as one-step fabrication, motion readout, and biodegradability render this micromotor an attractive candidate for sensing applications.