Micro/nanomotors (MNMs) are miniaturized machines that can perform assigned tasks at the micro/nanoscale. Over the past decade, significant progress has been made in the design, preparation, and applications of MNMs that are powered by converting different sources of energy into mechanical force, to realize active movement and fulfill on‐demand tasks. MNMs can be navigated to desired locations with precise controllability based on different guidance mechanisms. A considerable research effort has gone into demonstrating that MNMs possess the potential of biomedical cargo loading, transportation, and targeted release to achieve therapeutic functions. Herein, the recent advances of self‐propelled MNMs for on‐demand biomedical cargo transportation, including their self‐propulsion mechanisms, guidance strategies, as well as proof‐of‐concept studies for biological applications are presented. In addition, some of the major challenges and possible opportunities of MNMs are identified for future biomedical applications in the hope that it may inspire future research.

There are two main aspects of environmental governance including monitoring and remediation, both of which are essential for environmental protection. Self-propelled micro/nanomotors (MNM) have shown promising potential for achieving on-demand tasks in environmental field, including environmental sensing and pollutant removal or degradation. However, most of the current MNM used in environmental protection can hardly accomplish the two major tasks of both monitoring and pollutant degradation. Hereby, we present a bubble-propelled mesoporous silica-coated titania (TiO2@mSiO2) bilayer tubular micromotor with platinum (Pt) and magnetic Fe3O4 nanoparticles modified on their inner walls. The outer mesoporous silica (mSiO2) layer can effectively adsorb and collect the pollutants, and the adsorption capacity of the TiO2@mSiO2 tube is about 3 times higher than that of the TiO2 tube due to the presence of mSiO2 shell. By magnetic manipulation, the micromotors can be recovered to release the collected pollutant for precise analysis of the composition of the pollutants, such us pollutant molecule identification by surface-enhanced Raman scattering. The active motion and photocatalytic TiO2 inner layer of the micromotors can greatly enhance the degradation rate of the model pollutant rhodamine 6G (R6G). Our results show that within 30 min, up to 98% of R6G can be degraded by the motors. The successful demonstration of the TiO2@mSiO2 bilayer tubular motors for simultaneous environmental monitoring and pollutant degradation paves the way for future development of active and intelligent micro/nanorobots for advanced environmental governance.

This review focuses on the biocompatibility of micro/nano-motors (MNMs) with regard to the fabrication materials and propulsion mechanisms. The future prospective and suggestions on the development of MNMs towards practical biomedical applications are also proposed.

Photodynamic therapy (PDT), an alternative to conventional cancer therapeutics, has gained increasing attention for its noninvasive advantage and simultaneous fluorescence imaging property. PDT is a tripartite process that functions in the simultaneous presence of a photosensitizer (PS), light, and available oxygen molecules. However, many highly efficient PSs are hydrophobic and highly tend to self-aggregate in aqueous solution, leading to quick quenching of the PDT effect. Here we construct zeolitic imidazolate framework-8 (ZIF-8) containing water-insoluble photosensitizer zinc(II) phthalocyanine (ZnPc), a typical hydrophobic PS, by one-step coprecipitation process, named as ZnPc@ZIF-8. The micropores of ZIF-8 act as molecular cages to separate and maintain hydrophobic ZnPc in the monomeric state and protect it against self-aggregation, which enables the encapsulated ZnPc to generate cytotoxic singlet oxygen (O) under light irradiation (650 nm) in aqueous condition. The formed nanosystem of ZnPc@ZIF-8 can be endocytosed by cancer cells and exhibits red fluorescent emission with excellent photodynamic activity for cancer treatment in vitro. In addition, ZnPc@ZIF-8 is acid-sensitive and would completely degrade after PDT, which can be monitored by the self-quenching of fluorescence emission of ZnPc. This work paves a facile way for resolving the problem of solubility and bioavailability of hydrophobic PS by utilizing metal-organic frameworks as nanocarriers.

Surface-enhanced Raman scattering (SERS) has attracted increasing attention in the field of biochemical sensing since its discovery in 1970s, in virtue of its ultrahigh sensitivity to extremely low concentration of analyte. The performance of SERS biosensing strongly relies on the surface properties of SERS substrates, which are generally noble metallic nanoparticles. Surfactants have always been used for the preparation of nanoparticles to maintain the stability of nanocolloids, which greatly affect the efficiency of SERS sensing due to the space blocking between SERS substrates and analytes, as well as the interference of intrinsic Raman signals from surfactant themselves. Herein, without adding any surfactant, we synthesized nanosized graphene oxide (NGO) coated silver nanoparticles (Ag@NGO), which were used as efficient SERS substrates, taking the advantages of surfactant-free surface with inert protective effect of the GO shell. The Ag@NGO nanoparticles demonstrated excellent SERS sensing capability and can be used as biocompatible nanoprobes for intracellular biosensing. The π−π interaction between the anticancer drug of doxorubicin (DOX, a typical anticancer drug) and GO facilitates DOX loading onto Ag@NGO nanoparticles as drug delivery nanocarriers as well. Therefore, Ag@NGO holds great potential as a theranostic platform with capabilities of both SERS biosensing and drug delivery.

Micro/nano-motors (MNMs) that combine attributes of miniaturization and self-propelled swimming mobility have been explored for efficient environmental remediation in the past decades. However, their progresses in practical applications are now subject to several critical issues including a complicated fabrication process, low production yield, and high material cost. Herein, we propose a biotemplated catalytic tubular micromotor consisting of a kapok fiber (KF, abundant in nature) matrix and manganese dioxide nanoparticles (MnO2 NPs) deposited on the outer and inner walls of the KF and demonstrate its applications for rapid removal of methylene blue (MB) in real-world wastewater. The fabrication is straightforward via dipping the KF into a potassium permanganate (KMnO4) solution, featured with high yield and low cost. The distribution and amount of MnO2 can be easily controlled by varying the dipping time. The obtained motors are actuated and propelled by oxygen (O2) bubbles generated from MnO2-triggered catalytic decomposition of hydrogen peroxide (H2O2), with the highest speed at 615 μm/s (i.e., 6 body length per second). To enhance decontamination efficacy and also enable magnetic navigation/recycling, magnetite nanoparticles (Fe3O4 NPs) are adsorbed onto such motors via an electrostatic effect. Both the Fe3O4-induced Fenton reaction and hydroxyl radicals from MnO2-catalyzed H2O2 decomposition can account for the MB removal (or degradation). Results of this study, taken together, provide a cost-effective approach to achieve high-yield production of the MNMs, suggesting an automatous microcleaner able to perform practical wastewater treatment.

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