Self-sensing enzyme-powered micromotors equipped with pH responsive DNA nanoswitches.

Bio-catalytic micro- and nanomotors have emerged as a new class of active matter self-propelled through enzymatic reactions. The incorporation of functional nanotools could enable the rational design of multifunctional micromotors for simultaneous real-time monitoring of their environment and activity. Herein, we report the combination of DNA nanotechnology and urease-powered micromotors as multi-functional tools able to swim, simultaneously sense the pH of their surrounding environment and monitor their intrinsic activity. With this purpose, a FRET labelled triplex DNA nanoswitch for pH sensing was immobilized onto the surface of mesoporous silica based micromotors. During self-propulsion, urea decomposition and the subsequent release of ammonia led to a fast pH increase, which was detected by real-time monitoring of the FRET efficiency through confocal laser scanning microscopy at different timepoints (i.e. 30 s, 2 min and 10 min.). Furthermore, the analysis of speed, enzymatic activity and propulsive forces displayed a similar exponential decay, matching the trend observed for the FRET efficiency. These results illustrate the potential of using specific DNA nanoswitches not only for sensing the micromotors' surrounding microenvironment but also as an indicator of the micromotor activity status, which may aid to the understanding of their performance in different media and in different applications.