Self-/Magnetic-Propelled Catalytic Nanomotors Based on a Janus SPION@PEG-Pt/PCL Hybrid Nanoarchitecture: Single-Particle versus Collective Motions

In this paper, we synthesized superparamagnetic iron oxide nanoparticles (NPs) functionalized with (3-aminopropyl)­triethoxysilane (Fe₃O₄@APTES). The synthesized NPs were coated with succinic anhydride (Fe₃O₄@COOH) in the next step. Half the surface of the NPs was shielded with wax microparticles via the Pickering emulsion technique, and the unshielded side was covered with poly­(ethylene glycol) methyl ether. Platinum nanoparticles (Pt NPs) were deposited between PEG chains by the oxidation-reduction method through an in situ procedure to obtain a metal–polymer composite. These deposited Pt NPs have the potential to catalyze the decomposition of hydrogen peroxide at the surface of Janus nanomotors (JNMs). After de-waxing of the NPs, Irgacure 2959 (as the initiator) was reacted with the bare side of the NPs to provide the opportunity to grow poly­(ε-caprolactone) (PCL) chains on the surface of the nanomotors through the “grafting from” method. The diffusion coefficient and velocity of the JNMs (before and after the PCL reaction) in the aqueous solution of 1, 2, 3, 5, and 10% (w/w) hydrogen peroxide and in the presence of different concentrations of NaCl solutions (0, 5, and 10% (w/v)) were investigated by mean square displacement analysis for single-particle or collective motions of JNMs. In addition, the simultaneous effect of an external magnetic field and the NaCl concentration on the movement direction of JNMs was also evaluated in the presence of hydrogen peroxide (10%). Increasing the ionic strength through NaCl addition permits the JNMs to move with relatively lower amounts of fuel [i.e., 2% (w/w)]. The collective motion investigation of the JNMs showed the highest speed in the media with 10% (w/w) hydrogen peroxide and 5% (w/v) NaCl solution (about 1215.78 μm²/s) due to the surfactant effect of the Janus architecture.