Biocompatible micromotors for biosensing

Modified Au:Fe-Ni magnetic micromotors improve drug delivery and diagnosis in MCF-7 cells and spheroids

Nano/micromotors hold immense potential for revolutionizing drug delivery and detection systems, especially in the realm of cancer diagnosis and treatment, owing to their distinctive features, including precise propulsion, maneuverability, and meticulously designed surface modifications. In this study, we explore the capabilities of modified and magnetically driven micromotors as active drug delivery systems within 2D and 3D cell culture environments and cancer diagnosis. We synthesized gold (Au) and iron-nickel (Fe-Ni) metallic-based magnetic micromotors (Au:Fe-Ni MMs) through electrochemical methods, equipping them with functionalities for controlled doxorubicin (DOX) release and cancer cell recognition. In 2D and spheroids of MCF-7 adenocarcinoma cells, the Au segment of these micromotors was utilized to help DOX loading through poly(sodium-4-styrenesulfonate) (PSS) functionalization, and the attachment of antiHER2 antibodies for specific recognition. This innovative approach enabled controlled drug release within the cancerous microenvironment, coupled with magnetic (Fe-Ni) propulsion for biocompatible drug delivery to MCF-7 cells. Furthermore, antiHER2 immobilized Au:Fe-Ni MMs effectively interacted with receptors, capitalizing on the overexpression of HER2 antigens on MCF-7 cells. Encouraging outcomes were observed, particularly in spheroid models, underscoring the remarkable potential of these multifunctional micromotors for advancing intelligent drug delivery methodologies and diagnostic purposes.

Supramolecular Modular Assembly of Imaging-Trackable Enzymatic Nanomotors

Self-propelled micro/nanomotors (MNMs) have shown great application potential in biomedicine, sensing, environmental remediation, etc. In the past decade, various strategies or technologies have been used to prepare and functionalize MNMs. However, the current preparation strategies of the MNMs were mainly following the pre-designed methods based on specific tasks to introduce expected functional parts on the various micro/nanocarriers, which lacks a universal platform and common features, making it difficult to apply to different application scenarios. Here, we have developed a modular assembly strategy based on host-guest chemistry, which enables the on-demand construction of imaging-trackable nanomotors mounted with suitable driving and imaging modules using a universal assembly platform, according to different application scenarios. These assembled nanomotors exhibited enhanced diffusion behavior driven by enzymatic reactions. The loaded imaging functions were used to dynamically trace the swarm motion behavior of assembled nanomotors with corresponding fuel conditions both in vitro and in vivo. The modular assembly strategy endowed with host-guest interaction provides a universal approach to producing multifunctional MNMs in a facile and controllable manner, which paves the way for the future development of MNMs systems with programmable functions.

Chemical multiscale robotics for bacterial biofilm treatment

A biofilm constitutes a bacterial community encased in a sticky matrix of extracellular polymeric substances. These intricate microbial communities adhere to various host surfaces such as hard and soft tissues as well as indwelling medical devices. These microbial aggregates form a robust matrix of extracellular polymeric substances (EPSs), leading to the majority of human infections. Such infections tend to exhibit high resistance to treatment, often progressing into chronic states. The matrix of EPS protects bacteria from a hostile environment and prevents the penetration of antibacterial agents. Modern robots at nano, micro, and millimeter scales are highly attractive candidates for biomedical applications due to their diverse functionalities, such as navigating in confined spaces and targeted multitasking. In this tutorial review, we describe key milestones in the strategies developed for the removal and eradication of biofilms using robots of different sizes and shapes. It can be seen that robots at different scales are useful and effective tools for treating bacterial biofilms, thus preventing persistent infections, the loss of costly implanted medical devices, and additional costs associated with hospitalization and therapies.

Magnetic Janus micromotors for fluorescence biosensing of tacrolimus in oral fluids

Tacrolimus (FK506) is a macrolide lactone immunosuppressive drug that is commonly used in transplanted patients to avoid organ rejection. FK506 exhibits high inter- and intra-patient pharmacokinetic variability, making monitoring necessary for organ graft survival. This work describes the development of a novel bioassay for monitoring FK506. The bioassay is based on using polycaprolactone-based (PCL) magnetic Janus micromotors and a recombinant chimera receptor that incorporates the immunophilin tacrolimus binding protein 1A (FKBP1A) tagged with Emerald Green Fluorescent Protein (EmGFP). The approach relies on a fluorescence competitive bioassay between the drug and the micromotors decorated with a carboxylated FK506 toward the specific site of the fluorescent immunophilin. The proposed homogeneous assay could be performed in a single step without washing steps to separate the unbound receptor. The proposed approach fits the therapeutic requirements, showing a limit of detection of 0.8 ng/mL and a wide dynamic range of up to 90 ng/mL. Assay selectivity was evaluated by measuring the competitive inhibition curves with other immunosuppressive drugs usually co-administered with FK506. The magnetic propulsion mechanism allows for efficient operation in raw samples without damaging the biological binding receptor (FKBP1A-EmGFP). The enhanced target recognition and micromixing strategies hold considerable potential for FK506 monitoring in practical clinical use.

A novel magnetically guided, oxygen propelled CoPt/Au nanosheet motor in conjugation with a multilayer hollow microcapsule for effective drug delivery and light triggered drug release

In recent years, nanomotors have been developed and attracted extensive attention in biomedical applications. In this work, a magnetically-guided oxygen-propelled CoPt/gold nanosheet motor (NSM) was prepared and used as an active self-propelled platform that can load, transfer and control the release of drug carrier to cancer cells. As a drug carrier, the microcapsules were constructed by the layer-by-layer (LbL) coating of chitosan and carboxymethyl cellulose layers, followed by incorporation of gold and magnetite nanoparticles. Doxorubicin (DOX) as an anti-cancer drug was loaded onto the synthesized microcapsules with a loading efficiency of 77%. The prepared NSMs can deliver the DOX loaded magnetic multilayer microcapsule to the target cancer cell based on the catalytic decomposition of H2O2 solution (1% v/v) via guidance from an external magnetic force. The velocity of NSM was determined to be 25.1 μm s-1 in 1% H2O2. Under near-infrared irradiation, and due to the photothermal effect of the gold nanoparticles, the proposed system was found to rapidly release more drugs compared to that of an internal stimulus diffusion process. Moreover, the investigation of cytotoxicity of NSMs and multilayer microcapsules clearly revealed that they have negligible side effects over all the concentrations tested.

Focus on the performance enhancement of micro/nanomotor-based biosensors

Micro/nanomotors (MNMs) emerge as a vital candidate for biosensing due to its nano-size structure, high surface-to-area ratio, directional mobility, biocompatibility, and ease of functionalization, therefore being able to detect objects with high efficiency, precision, and selectivity. The driving mode, nanostructure, materials property, preparation technique, and biosensing applications have been thoroughly discussed in publications. To promote the MNMs-based biosensors from in vitro to in vivo, it is necessary to give a comprehensive discussion from the perspective of sensing performances enhancement. However, until now, there is few reviews dedicated to the systematic discussion on the multiple performance enhancement schemes and the current challenges of MNMs-based biosensors. Bearing it in mind and based on our research experience in this field, we summarized the enhancement methods for biosensing properties such as sensitivity, selectivity, detection time, biocompatibility, simplify system operation, and environmental availability. We hope that this review provides the readers with fundamental understanding on performance enhancement schemes for MNMs-based biosensors.

Fabrication and open-loop control of three-lobed nonspherical Janus microrobots

In this study, we propose a simple and efficient method to fabricate three-lobed nonspherical Janus microrobots. These microrobots can be actuated by a harmless magnetic field. Utilizing organosilica as the material of choice, we leverage its versatile silane chemistry to enable various surface modifications and functionalities. The fabricated microrobots demonstrate two distinct modes of motion, making them well-suited for cell transportation and drug delivery tasks. Their unique shape and motion characteristics allow for precise and targeted movement. Integrating these microrobots into therapeutic delivery platforms can revolutionize medical treatments, offering enhanced precision, efficiency, and versatility in delivering therapies to specific sites.

Intelligent sensing based on active micro/nanomotors

In the microscopic world, synthetic micro/nanomotors (MNMs) can convert a variety of energy sources into driving forces to help humans perform a number of complex tasks with greater ease and efficiency. These tiny machines have attracted tremendous attention in the field of drug delivery, minimally invasive surgery, in vivo sampling, and environmental management. By modifying their surface materials and functionalizing them with bioactive agents, these MNMs can also be transformed into dynamic micro/nano-biosensors that can detect biomolecules in real-time with high sensitivity. The extensive range of operations and uses combined with their minuscule size have opened up new avenues for tackling intricate analytical difficulties. Here, in this review, various driving methods are briefly introduced, followed by a focus on intelligent detection techniques based on MNMs. And we discuss the distinctive advantages, current issues, and challenges associated with MNM-based intelligent detection. It is believed that the future advancements of MNMs will greatly impact the diagnosis, treatment, and prevention of diseases.

The rise of metal-organic framework based micromotors

Micromotors (MMs) are micro and nanoscale devices capable of converting energy into autonomous motion. Metal-organic frameworks (MOFs) are crystalline materials that display exceptional properties such as high porosity, internal surface areas, and high biocompatibility. As such, MOFs have been used as active materials or building blocks for MMs. In this highlight, we describe the evolution of MOF-based MMs, focusing on the last 3 years. First, we covered the main propulsion mechanisms and designs, from catalytic to fuel-free MOF-based MMs. Secondly, we discuss recent applications of new fuel-free MOFs MM to give a critical overview of the current challenges of this blooming research field. The advantages and challenges discussed provide a useful guide for the design of the next generation MOF MMs toward real-world applications.

Advancements in artificial micro/nanomotors for nucleic acid biosensing: a review of recent progress

Artificial micro/nanomotors represent a class of well-designed tools that exhibit dynamic motion and remote-control capabilities, endowing them with the capacity to perform complex tasks at the micro/nanoscale. Their utilization in nucleic acid biosensing has been paid significant attention, owing to their ability to facilitate targeted delivery of detection probes to designated sites and enhance hybridization between detection probes and target nucleic acids, thereby improving the sensitivity and specificity of biosensing. Within this comprehensive overview, we elucidate the advancement of nucleic acid biosensing through the integration of micro/nanomotors over the past decade. In particular, we provide an in-depth exploration of the diverse applications of micro/nanomotors in nucleic acid biosensing, including fluorescence recovery-based biosensing, velocity change-based biosensing, and aggregation-enhanced biosensing. Additionally, we outline the remaining challenges that impede the practical application of artificial micro/nanomotors in nucleic acid detection, and offer personal insights into prospective avenues for future development. By overcoming these obstacles, we anticipate that artificial micro/nanomotors will revolutionize conventional nucleic acid detection methodologies, providing enhanced sensitivity and reduced diagnostic timeframes, thereby facilitating more effective disease diagnosis.

Recent progress of micro/nanomotors to overcome physiological barriers in the gastrointestinal tract

Oral administration is a convenient administration route for gastrointestinal disease therapy with good patient compliance. But the nonspecific distribution of the oral drugs may cause serious side effects. In recent years, oral drug delivery systems (ODDS) have been applied to deliver the drugs to the gastrointestinal disease sites with decreased side effects. However, the delivery efficiency of ODDS is tremendously limited by physiological barriers in the gastrointestinal sites, such as the long and complex gastrointestinal tract, mucus layer, and epithelial barrier. Micro/nanomotors (MNMs) are micro/nanoscale devices that transfer various energy sources into autonomous motion. The outstanding motion characteristics of MNMs inspired the development of targeted drug delivery, especially the oral drug delivery. However, a comprehensive review of oral MNMs for the gastrointestinal diseases therapy is still lacking. Herein, the physiological barriers of ODDS were comprehensively reviewed. Afterward, the applications of MNMs in ODDS for overcoming the physiological barriers in the past 5 years were highlighted. Finally, future perspectives and challenges of MNMs in ODDS are discussed as well. This review will provide inspiration and direction of MNMs for the therapy of gastrointestinal diseases, pushing forward the clinical application of MNMs in oral drug delivery.

Autonomous Microlasers for Profiling Extracellular Vesicles from Cancer Spheroids

Self-propelled micro/nanomotors are emergent intelligent sensors for analyzing extracellular biomarkers in circulating biological fluids. Conventional luminescent motors are often masked by a highly dynamic and scattered environment, creating challenges to characterize biomarkers or subtle binding dynamics. Here we introduce a strategy to amplify subtle signals by coupling strong light-matter interactions on micromotors. A smart whispering-gallery-mode microlaser that can self-propel and analyze extracellular biomarkers is demonstrated through a liquid crystal microdroplet. Lasing spectral responses induced by cavity energy transfer were employed to reflect the abundance of protein biomarkers, generating exclusive molecular labels for cellular profiling of exosomes derived from 3D multicellular cancer spheroids. Finally, a microfluidic biosystem with different tumor-derived exosomes was employed to elaborate its sensing capability in complex environments. The proposed autonomous microlaser exhibits a promising method for both fundamental biological science and applications in drug screening, phenotyping, and organ-on-chip applications.

Electrokinetic Active Particles for Motion-Based Biomolecule Detection

Detection of biomolecules is essential for patient diagnosis, disease management, and numerous other applications. Recently, nano- and microparticle-based detection has been explored for improving traditional assays by reducing required sample volumes and assay times as well as enhancing tunability. Among these approaches, active particle-based assays that couple particle motion to biomolecule concentration expand assay accessibility through simplified signal outputs. However, most of these approaches require secondary labeling, which complicates workflows and introduces additional points of error. Here, we show a proof-of-concept for a label-free, motion-based biomolecule detection system using electrokinetic active particles. We prepare induced-charge electrophoretic microsensors (ICEMs) for the capture of two model biomolecules, streptavidin and ovalbumin, and show that the specific capture of the biomolecules leads to direct signal transduction through ICEM speed suppression at concentrations as low as 0.1 nM. This work lays the foundation for a new paradigm of rapid, simple, and label-free biomolecule detection using active particles.

Catalytic Micromotors as Self-stirring Microreactors for Efficient Dual-mode Colorimetric Detection

A catalytic micromotor-based (MIL-88B@Fe₃O₄) colorimetric detection system which exhibit rapid color reaction for quantitative colorimetry and high-throughput testing for qualitative colorimetry have been successfully developed. Taking the advantages of the micromotor with dual roles (micro-rotor and micro-catalyst), under rotating magnetic field, each micromotor represents a microreactor which have micro-rotor for microenvironment stirring and micro-catalyst for the color reaction. Numerous self-string micro-reactions rapidly catalyze the substance and show the corresponding color for the spectroscopy testing and analysis. Additionally, owing to the tiny motor can rotate and catalyze within microdroplet, a high-throughput visual colorimetric detection system with 48 micro-wells has been innovatively conducted. The system enables up to 48 microdroplet reactions based on micromotors run simultaneously under the rotating magnetic field. Multi-substance, including their species difference and concentration strength, can be easily and efficiently identified by observing the color difference of the droplet with naked eye after just one test. This novel catalytic MOF-based micromotor with attractive rotational motion and excellent catalytic performance not only endowed a new nanotechnology to colorimetry, but also shows hold great potentials in other fields, such as refined production, biomedical analysis, environmental governance etc., since such micromotor-based microreactor can be easily applied to other chemical microreactions.