At present, antibacterial agents, such as antibiotics, antimicrobial peptides and metal cations, can only be passively delivered through the circulatory system, which has poor targeting and low retention rate in vivo, and is difficult to achieve the desired therapeutic effect. Repeated administration not only easily induces the formation of drug-resistant bacteria, but also produces greater toxic and side effects on normal tissues^[51]. Micro-nanorobot as a carrier to deliver antimicrobial agents can significantly improve the therapeutic effect. Its excellent motion performance can not only enhance the diffusion and retention of drugs in the lesion site, but also promote the combination of drugs and bacteria, which provides a new strategy for efficient delivery of antimicrobial agents^[43,52,53]. Gademann et al. Developed a bio-driven active microrobot using Chlamydomonas reinhardtii as a drug delivery vehicle (Fig. 2A)^[29,30]. By loading antibiotics such as vancomycin and ciprofloxacin on the surface of Chlamydomonas reinhardtii, the drugs can be transported by the movement of Chlamydomonas reinhardtii, and the transport direction can be controlled by the inherent phototaxis of algae to transport the drugs to the bacterial infection area directionally and release the antibiotics on demand. Wang et al. Used the microalgae biohybrid robot in a mouse model of acute Pseudomonas aeruginosa pneumonia to verify the ability of the robot to escape alveolar macrophage clearance and excellent antibacterial ability, which greatly improved drug retention, improved treatment efficiency and reduced animal mortality^[31]. Bandyopadhyay et al. Used the porous structure in the natural edible Agaricus bisporus tissue to load the antibacterial substance curcumin, which combined with the inherent antibacterial active substance in the mushroom body to show enhanced antibacterial effect. In addition, by loading magnetite nanoparticles on the surface, it can be endowed with magnetic drive function, so as to precisely control its movement direction and achieve active antibacterial^[54]. Pumera et al. Modified the microrobot with indolmycin peptide (Fig. 2B), using the high affinity of indolmycin peptide to the bacterial membrane, selectively enriched in the interfacial region of the bacterial lipid bilayer, inhibited bacterial DNA replication, and caused the bacterial membrane to become filamentous, thereby inhibiting bacterial reproduction and further eradicating the biofilm produced by Methicillin-resistant Staphylococcus aureus (MRSA)^[45]. Gu et al. Utilized a PEDOT/MnO₂ tubular micromotor loaded with silver ion (Ag⁺) antibacterial agent with excellent antibacterial ability (Fig. 2C), which can achieve more efficient movement ability and enhanced diffusion ability through the synergistic catalytic effect of MnO₂ and Ag.The motor can rapidly move in a 0. 2% E. coil environment and kill 90% of Escherichia coli (E. coil) in solution within 10 min, providing a new antibiotic-free treatment strategy for bacterial infections^[26]. To sum up, micro-nano robots carry various antibacterial agents through porous structure or surface modification, and then precisely deliver them to bacterial infection areas by driving methods such as biological phototaxis and magnetic field navigation.Compared with the traditional method of passive delivery through the circulatory system, the antimicrobial delivery strategy with micro-nano robots as carriers not only significantly improves the antimicrobial effect, but also minimizes the toxic and side effects on normal cells and tissues.

Photothermal antibacterial is a new type of green therapy, the principle of which is to convert the energy of near-infrared light of photothermal agent into heat energy to increase the local temperature to achieve the purpose of thermal ablation treatment of bacterial infection. Photothermal therapy is safe, non-invasive, accurate and efficient, and does not require the use of antibiotics, so it avoids the generation of drug-resistant bacteria and has good application and transformation prospects^[55][56]. The good cargo loading and targeted delivery capabilities of micro-nano robots provide new ideas for photothermal antimicrobial therapy, by using materials with photothermal properties to develop robots or loading photothermal agents on the surface or inside of robots.The autonomous cruise of the robot transports the photothermal agent directionally to the lesion site, providing targeted photothermal agent enrichment for thermal ablation, thus effectively improving the efficiency of photothermal therapy. Yan et al. Modified magnetite nanoparticles on the surface of Spirulina to provide the robot with magnetic driving performance and excellent photothermal performance, which realized effective driving and precise control in a variety of fluid environments, and achieved efficient killing of E. coil when the temperature was raised to more than 50 ℃ under 808 nm laser irradiation for 6 min^[46]. In addition, the surface of the magnetic spirulina robot is coated with polydopamine, which can achieve enhanced photothermal therapy under the guidance of photoacoustic imaging (Figure 3)^[57]. Cai et al. Loaded copper sulfide (CuS) nanoparticles with excellent photothermal performance and good biosafety inside the magnetic microrobot, and verified the robot's photothermal killing ability of E. coil in vitro^[47]. To sum up, using photothermal materials to develop or functionalize micro-nano robots can realize the "active" transportation and delivery of photothermal agents under the autonomous movement and precise control of robots, promote the enrichment of photothermal agents at the site of bacterial infection, and then realize the enhanced photothermal antibacterial therapy of micro-nano robots, providing a new strategy for photothermal antibacterial therapy.

PDT is also one of the commonly used antibacterial methods. When the photosensitizer is excited by an external light source, it transfers energy to the surrounding oxygen molecules to produce Reactive oxygen species (ROS), which then reacts with the surrounding biological macromolecules to produce cytotoxicity and effectively kill bacterial cells^[58]. Micro-nanorobot can be used as a mobile photosensitizer platform to improve the utilization of oxygen molecules and the diffusion range of ROS by autonomous movement at the site of bacterial infection, thus achieving more efficient PDT. Ma et al. Developed a magnetic hollow mesoporous SiO₂ micromotor (MHSTU) containing 5,10,15,20-tetrakis (4-aminophenyl) porphyrin (TAPP, a highly efficient hydrophobic photosensitizer) as a mobile photosensitizer platform (Figure 4A)^[14]. On the one hand, the motor can be transported to the focus area remotely and directionally through the action of an external magnetic field, and on the other hand, the motor can enhance the movement of the focus area based on chemical drive, thereby enhancing the photodynamic toxicity and improving the antibacterial effect. Pumera et al. Proposed a hybrid enzyme/photocatalytic microrobot based on TiO₂/CdS nanotube bundles (Fig. 4 B), which can be propelled autonomously in urea^[48]. Photoactivated by visible light, the photocatalytic counterpart based on TiO₂/CdS nanotube bundles generates ROS, which produces a phototoxic effect on the biofilm surface and can remove nearly 90% of the bacterial biofilm. To sum up, under the mediation of micro-and nano-robots, photosensitizers can efficiently combine with surrounding oxygen molecules, produce a large number of ROS while promoting their diffusion, improve antibacterial efficiency, and achieve photodynamic therapy enhanced by micro-and nano-robots. This green and efficient antibacterial technology can complete controllable and repeatable treatment in specific lesion areas, but the applicability of PDT in deep tissues is low due to the limited depth of light penetration.

Mechanical damage is an effective way to resist bacteria. Micro-nano robots can produce certain mechanical force through movement and deformation, which can destroy the bacterial biofilm and cause a certain degree of mechanical damage to bacteria^[59,60]. Song et al. Developed a micro-robot with high affinity to Staphylococcus aureus (S. aureus) by using magnetotactic bacteria MO-1. Under the action of an oscillating magnetic field, the robot can swing with the change of the magnetic field and attach to the surface of bacteria, while generating mechanical force to apply shear force to the attached S. aureus, resulting in the death of bacteria^[28]. At the same time, this strategy was used to treat S. aureus infected wounds, and the wound healing was significantly improved^[61]. Subsequently, they designed a magnetic target device that can generate focusing, rotating and oscillating magnetic fields to optimize the control strategy of the robot^[15]. Firstly, the robot moves around the bacteria under the action of a focused magnetic field, and then a rotating magnetic field is applied to quickly mix the robot with the bacteria to enhance the adhesion between the robot and the bacteria, and then the bacteria are killed under the action of an oscillating magnetic field. The "guiding-mixing-sterilization" integrated antimicrobial therapy strategy of micro-nano robots has greatly improved the accuracy and efficiency of targeted therapy. Truong et al. Used magnetically responsive liquid metal (GLM-Fe) droplets to disrupt biofilms of Pseudomonas aeruginosa and S. aureus (Fig. 5A)^[49].

Under the action of a low-intensity rotating magnetic field, GLM-Fe is physically driven to deform into droplets with sharp edges. When in contact with the bacterial biofilm, the particle motion generated by the magnetic field synergizes with the nano-sharp edges to achieve the physical disruption of the bacterial cell and the breakdown of the dense biofilm matrix. In addition, magnetic liquid metal is loaded into the interior of pollen with microspines, and the natural microspines inherent in pollen and the sharp edges formed by the deformation of liquid metal can provide mechanical force to actively destroy the dense biological matrix and embedded bacterial cells, and finally achieve synergistic eradication of the complex mixture of bacterial biofilms within the biliary stent (Fig. 5 B)^[50]. To sum up, micro-nano robots can use magnetic field to achieve precise and efficient mechanical force antibacterial strategy, and switch different magnetic field types according to needs.In response, the micro-nano robot can quickly move to the bacterial area and disperse and adhere to the bacterial surface, and then use the rotating cluster effect to generate a certain intensity of mechanical shear force to achieve the purpose of anti-bacterial by damaging bacterial cells through mechanical force.

Each of the above treatment methods has its own merits in terms of antimicrobial application, and by integrating the advantages of various treatment strategies, it is expected to achieve more efficient antimicrobial treatment^[38,62]. Mao et al. Fabricated an Indocyanine green (ICG) -loaded Au@ZnO@SiO₂-ICG Janus nanomotor (Fig. 6A), constructing a synergistic antibacterial platform with photothermal and photodynamic properties triggered by dual light sources^[63]. ZnO can produce cytotoxic ROS under UV irradiation, while Au @ ZnO can regulate electron transfer under UV irradiation, thus effectively enhancing PDT, and the loaded ICG, as a photosensitizer, can also effectively enhance ROS production.At the same time, ICG has a strong absorption property in near-infrared light, can induce a strong photothermal effect, and cooperates with Au to generate a stronger photothermal effect under near-infrared light, thereby realizing an enhanced PDT and PTT synergistic effect and effectively killing E. coil and S. aureus. Koo et al. Designed a magnetic antibacterial robot loaded with nanoenzyme (Fig. 6B), which uses iron oxide to catalyze H₂O₂ to produce ROS and kill bacteria, while using nanoenzyme to specifically degrade the extracellular matrix of Streptococcus mutans biofilm.The mechanical force generated by the magnetic drive robot is used to remove biofilm residues and prevent biofilm regeneration, and the integration of "killing, degradation and removal" is successfully realized to combat persistent biofilm infection^[64]. Ma et al. Coated polydopamine with excellent photothermal properties on the surface of enzyme-driven liquid metal nanomotor, and loaded antibacterial drug cefixime trihydrate, used the enhanced photothermal effect of liquid metal and polydopamine coating and the chemotherapeutic effect of antibiotics to resist E. coil, and realized the image localization tracking in mouse bladder^[65]. To sum up, based on the application of micro-nano robots in antibacterial therapy, the design integrates various therapies and develops micro-nano robot synergistic antibacterial therapy strategies, such as "PDT + PTT synergy", "antibacterial agent delivery + mechanical force killing synergy", etc., to enhance the efficacy through the integration of advantages and achieve safer and more efficient antibacterial therapy^[66].