Study On PH-responsive Motion Behaviors Of Flask-like Carbonaceous Motors Based On Fe₃O₄ Nanoenzymes

The pH-responsive micro/nanomotors are artificial micro/nanodevices that can sense the pH change of the surrounding environment and transmit a readable signal to the outside world.Since many aspects,such as chemical reactions,environmental monitoring,food identification and so on,are closely related to pH,pH-responsive micro/nanomotors are of great practical significance.Especially in the detection of trace samples,such as the biomedical field,its small size and autonomous motion characteristics can show great advantages.In addition to the field of in vitro sensing,pH-responsive micro/nanomotors are also expected to enable future in vivo applications,such as utilizing the properties of pH gradient dysregulation in tumor microenvironments for disease treatment.Although great progress has been made in pH-responsive micro/nanomotors,the imperfections of poor biocompatibility,high preparation cost,large size,monotonous or single-point response and single function limit their wide application.limited its scope of application.Therefore,in this paper,the magnetic Fe₃O₄ nanozymes and the hollow bottle-shaped bio-based hydrothermal carbon materials were combined to prepare a carbon bottle-shaped micro-nanomotor with good magnetic properties and biocompatibility,so as to realize the responsive motion to environmental pH.This research is mainly carried out from the following two parts:Firstly,a high-temperature thermal decomposition method was used to prepare different properties of Fe₃O₄ magnetic nanoparticles in the oil phase by adjusting the three experimental parameters of reaction temperature,reaction time and raw material ratio;Its surface was modified with DMSA and transformed into water-soluble Fe₃O₄nanozyme that can be widely used.The results show that the enzyme-like catalytic activity of nanoparticles generally follows the"size law",that is,the smaller the size,the stronger the catalytic activity.After surface modification with DMSA,water-soluble Fe₃O₄ nanozyme with good dispersibility was obtained,and it could maintain high saturation magnetization and enzyme-like catalytic activity.In addition,the catalytic activity of the nanozyme is affected by the concentration of the substrate H₂O₂and the pH of the environment,showing different catalytic behaviors,which lays the foundation for the study of responsive micro/nanomotors in the following.Secondly,a flask-like bio-based hydrothermal carbon material with a size of about600 nm and a cavity diameter of about 280 nm prepared by a soft template-hydrothermal method was used as a carrier to encapsulate magnetic Fe₃O₄ nanozymes with a size of about 4 nm.A kind of flask-like carbonaceous nanomotors（FCNMs）with good biocompatibility was constructed.The results showed that FCNMs with good dispersity were successfully constructed,in which Fe₃O₄ nanozymes accounted for about 10.22 wt%,so they had certain magnetic properties,and their saturation magnetization was about 7.4 emu/g.FCNMs can sense changes in environmental pH and exhibit different motion behaviors.On the one hand,it is the movement speed change,which decreases to a minimum value of 5.98±0.46μm/s at pH 5.6 and increases to a maximum value of 7.53±1.0μm/s（≈12.4 body lengths s）at pH 6.8.Another aspect is the pH chemotactic motion behavior of FCNMs,which can spontaneously move along a pH gradient from 7.4 to 6.8.In addition,FCNMs can also exhibit excellent magnetic response motion performance.On the one hand,in the actual application process,the external magnetic field can realize the sensitive control of the movement direction of the motor;on the other hand,after the use is completed,the motors can be quickly separated and recycled through the external magnetic field.This study provides an effective strategy for the design and construction of adaptive pH-responsive micro/nanomotors,and because of its unique and controllable responsive movement behavior in physiological pH range,it also provides a possibility for the application of motors in biomedical fields,especially in targeted therapy of tumors.