Tuning the motion velocity of enzyme-driven dextran/polyacrylamide Janus nanomotors by incorporating the thermo-switchable PNIPAM moieties in their structure

Micro/nanomotors are miniaturized human-made devices capable of converting various forms of energy into movement. Over the past decades, a variety of micro/nanomotors with unique morphologies and different propulsion mechanisms have been developed. Enzyme-powered nanomotors have emerged as novel platforms in the biomedical field due to biocompatibility, versatility, and fuel bioavailability. Herein, we synthesized Janus enzymatic nanomotors based on magnetic iron oxide nanoparticles as a core. The two distinct faces of the magnetite structure were covered by dextran and a thermo-responsive terpolymer (N-isopropyl acrylamide-co-acrylamide-co-allylamine (NIPAM-co-AAm-co-AA) terpolymer) using the masking method. The Candida Antarctica lipase B (CALB) was used as the catalytic fuel of these nanoparticles and physically immobilized in the nanoparticles in different amounts for about 5, 10, 15, and 20 wt% of the nanoparticles to provide multi-stimuli propelled Janus nanomotors. After the enzymatic degradation of the modified dextran's ester groups, the nanoparticles begin to move. Optical microscopy studies indicated that the nanomotors had only a Brownian motion without the fuel (CALB enzyme). We found that the velocity motion of Janus nanomotors changed by immobilizing different enzyme concentrations in the nanoparticles. Based on the results, the lowest enzyme concentration required for the optimal hydrolysis rate of the ester group was determined to be 5% by weight of nanoparticles, and the maximum speed of nanomotors was determined at 15% by weight of nanoparticles. The effect of near-infrared (NIR) light on the velocity of nanomotors containing 15 wt% of CALB enzyme was investigated. It was found that the NIR light decreases the movement speed of these particles.