Self-Sensing Enzyme-Powered Micromotors Equipped with pH-Responsive DNA Nanoswitches

Abstract

Biocatalytic 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 multifunctional tools able to swim, simultaneously sense the pH of their surrounding environment, and monitor their intrinsic activity. With this purpose, a FRET-labeled triplex DNA nanoswitch for pH sensing was immobilized onto the surface of mesoporous silica-based micromotors. During selfpropulsion, urea decomposition and the subsequent release of ammonia led to a fast pH increase, which was detected by realtime monitoring of the FRET efficiency through confocal laser scanning microscopy at different time points (i.e., 30 s, 2 and 10 min). Furthermore, the analysis of speed, enzymatic activity, and propulsive force 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.

Recent Advances in Motion Control of Micro/Nanomotors

“…Cargo delivery [120] Cell-membrane-coated bacteria Blood circulation Tumor imaging [121] Cell hybrid Red blood cell-mimicking micromotor Ultrasound energy and magnetotactic control Oxygen transportation [16] Platelet-camouflaged nanorobots Magnetic propulsion and magnetotactic control Isolation of biological threats [124] Macrophage-Mg biohybrid motors Hydrogen bubble propulsion Endotoxin neutralization [125] Neutrophil-based micromotors Cell-driven and chemotactic control Target drug delivery [126] Enzyme-propelled Enzyme-powered microshell motors Catalase-trigged bubble propulsion and chemotactic control, size Drug delivery [141] Mesoporous silica-based nanomotors Urease-powered and pH responsive Target drug delivery [142] Micromotors equipped with DNA nanoswitches Urease-powered and pH responsive Microenvironment sensing and micromotor activity status indicator [143] Ultrasmall stomatocyte motors Biocatalyst catalase and chemotactic control Drug delivery [144] capability through the whole process of performing tasks. Also, the single chemotaxis to the egg cells restricts the potential application of this biohybrid machines.…”

“…Reproduced with permission. [143] Copyright 2019, American Chemical Society. D) Schematic diagram of the enzyme-powered nanomotors with controlled size for biomedical applications.…”

“…It is interesting to note that this special nanomotor is capable to "sense" the environment and deliver and release the active molecules on demand in response to predefined stimuli. Patino et al [143] reported mesoporous silica-based urease-powered micromotors ( Figure 12C) equipped with pH-responsive DNA nanoswitches, which are not only capable to sense the pH of surrounding environment but also as indicators of the activity status of the micromotors, promoting the understanding of their performance in different media and in different applications.…”

Biocatalytic Micro‐ and Nanomotors

“…A series of MSP‐based micro‐ and nanomotors were developed by the chemical conjugation of CAT, UR, and an ensemble of CAT/GOx or CAT/UR/GOx . Their half‐coating with SiO 2 , gold, nickel, or an iron layer resulted in a Janus two‐faced asymmetric structure of particles, of which the last two coatings provided micro‐/nanomotors with magnetic remote control.…”

“…Urea is present in human saliva (3–10 m m ), in human blood (2.6–6.5 m m ), and with up to a 50‐fold higher concentration with high variation in human urine . Nanomotors utilizing urea as a fuel were shown to deliver the drug doxorubicin to cancer cells more efficiently than that of a passive delivery system or to be pH‐responsive upon modification with DNA nanoswitches …”