Recent advances in micro/nanomotors for antibacterial applications

Currently, the rapid spread of multidrug-resistant bacteria derived from the indiscriminate use of traditional antibiotics poses a significant threat to public health worldwide. Moreover, established bacterial biofilms are extremely difficult to eradicate because of their high tolerance to traditional antimicrobial agents and extraordinary resistance to phagocytosis. Hence, it is of universal significance to develop novel robust and efficient antibacterial strategies to combat bacterial infections. Micro/nanomotors exhibit many intriguing properties, including enhanced mass transfer and micro-mixing resulting from their locomotion, intrinsic antimicrobial capabilities, active cargo delivery, and targeted treatment with precise micromanipulation, which facilitate the targeted delivery of antimicrobials to infected sites and their deep permeation into sites of bacterial biofilms for fast inactivation. Thus, the ideal antimicrobial activity of antibacterial micro/nanorobots makes them desirable alternatives to traditional antimicrobial treatments and has aroused extensive interest in recent years. In this review, recent advancements in antibacterial micro/nanomotors are briefly summarized, focusing on their synthetic methods, propulsion mechanism, and versatile antibacterial applications. Finally, some personal insights into the current challenges and possible future directions to translate proof-of-concept research to clinic application are proposed.

Sulfur-encapsulated zeolite micromotors for the selective removal of cesium from high-salt water with accelerated cleanup times

Bubble-propelled sulfur-encapsulated NaX zeolite (S-NaX) micromotors were developed for the selective removal of cesium from high-salt conditions with accelerated cleanup times. NaX was first modified with sulfur to provide additional Lewis acid-base interactions with Cs⁺ for enhanced Cs⁺ selectivity, and then Pt was half-deposited on S-NaX for bubble propulsion via the catalytic decomposition of H₂O₂. The average velocity of the resulting S-NaX/Pt micromotors in 5 wt% H₂O₂ is 39.7 ± 17.1 μm/s, which is higher than that of a previously reported Cs adsorbent micromotor (35.4 μm/s). The Cs⁺ ion-exchange kinetics of the S-NaX micromotor is 1.32 times higher than that of the NaX micromotor in a 5 wt% H₂O₂ solution where the molar ratio of Na⁺ to Cs⁺ is 200, even though the sulfur in the S-NaX micromotor causes an adverse effect on the propulsion speed due to the sulfur poisoning effect. Moreover, the S-NaX micromotor in simulated groundwater also exhibited excellent Cs⁺ removal performance with distribution coefficient (K_d) values at least 3.2 times higher than those of the nonpropelled S-NaX and NaX micromotor, demonstrating the great potential for the treatment of radioactive Cs⁺-contaminated water.