Bacterial isolation by lectin-modified microengines

Sweet Janus Particles: Multifunctional Inhibitors of Carbohydrate-Based Bacterial Adhesion

Escherichia coli and other bacteria use adhesion receptors, such as FimH, to attach to carbohydrates on the cell surface as the first step of colonization and infection. Efficient inhibitors that block these interactions for infection treatment are multivalent carbohydrate-functionalized scaffolds. However, these multivalent systems often lead to the formation of large clusters of bacteria, which may pose problems for clearing bacteria from the infected site. Here, we present Man-containing Janus particles (JPs) decorated on one side with glycomacromolecules to target Man-specific adhesion receptors of E. coli. On the other side, poly(N-isopropylacrylamide) is attached to the particle hemisphere, providing temperature-dependent sterical shielding against binding and cluster formation. While homogeneously functionalized particles cluster with multiple bacteria to form large aggregates, glycofunctionalized JPs are able to form aggregates only with individual bacteria. The formation of large aggregates from the JP-decorated single bacteria can still be induced in a second step by increasing the temperature and making use of the collapse of the PNIPAM hemisphere. This is the first time that carbohydrate-functionalized JPs have been derived and used as inhibitors of bacterial adhesion. Furthermore, the developed JPs offer well-controlled single bacterial inhibition in combination with cluster formation upon an external stimulus, which is not achievable with conventional carbohydrate-functionalized particles.

Multi-Stimuli-Responsive Tadpole-like Polymer/Lipid Janus Microrobots for Advanced Smart Material Applications

Microrobots are of significant interest due to their smart transport capabilities, especially for precisely targeted delivery in dynamic environments (blood, cell membranes, tumor interstitial matrixes, blood-brain barrier, mucosa, and other body fluids). To perform a more complex micromanipulation in biological applications, it is highly desirable for microrobots to be stimulated with multiple stimuli rather than a single stimulus. Herein, the biodegradable and biocompatible smart micromotors with a Janus architecture consisting of PrecirolATO 5 and polycaprolactone compartments inspired by the anisotropic geometry of tadpoles and sperms are newly designed. These bioinspired micromotors combine the advantageous properties of polypyrrole nanoparticles (NPs), a high near-infrared light-absorbing agent with high photothermal conversion efficiency, and magnetic NPs, which respond to the magnetic field and exhibit multistimulus-responsive behavior. By combining both fields, we achieved an "on/off" propulsion mechanism that can enable us to overcome complex tasks and limitations in liquid environments and overcome the limitations encountered by single actuation applications. Moreover, the magnetic particles offer other functions such as removing organic pollutants via the Fenton reaction. Janus-structured motors provide a broad perspective not only for biosensing, optical detection, and on-chip separation applications but also for environmental water treatment due to the catalytic activities of multistimulus-responsive micromotors.

Collective Molecular Machines: Multidimensionality and Reconfigurability

Molecular machines are key to cellular activity where they are involved in converting chemical and light energy into efficient mechanical work. During the last 60 years, designing molecular structures capable of generating unidirectional mechanical motion at the nanoscale has been the topic of intense research. Effective progress has been made, attributed to advances in various fields such as supramolecular chemistry, biology and nanotechnology, and informatics. However, individual molecular machines are only capable of producing nanometer work and generally have only a single functionality. In order to address these problems, collective behaviors realized by integrating several or more of these individual mechanical units in space and time have become a new paradigm. In this review, we comprehensively discuss recent developments in the collective behaviors of molecular machines. In particular, collective behavior is divided into two paradigms. One is the appropriate integration of molecular machines to efficiently amplify molecular motions and deformations to construct novel functional materials. The other is the construction of swarming modes at the supramolecular level to perform nanoscale or microscale operations. We discuss design strategies for both modes and focus on the modulation of features and properties. Subsequently, in order to address existing challenges, the idea of transferring experience gained in the field of micro/nano robotics is presented, offering prospects for future developments in the collective behavior of molecular machines.

Recent Developments in Metallic Degradable Micromotors for Biomedical and Environmental Remediation Applications

Synthetic micromotor has gained substantial attention in biomedicine and environmental remediation. Metal-based degradable micromotor composed of magnesium (Mg), zinc (Zn), and iron (Fe) have promise due to their nontoxic fuel-free propulsion, favorable biocompatibility, and safe excretion of degradation products Recent advances in degradable metallic micromotor have shown their fast movement in complex biological media, efficient cargo delivery and favorable biocompatibility. A noteworthy number of degradable metal-based micromotors employ bubble propulsion, utilizing water as fuel to generate hydrogen bubbles. This novel feature has projected degradable metallic micromotors for active in vivo drug delivery applications. In addition, understanding the degradation mechanism of these micromotors is also a key parameter for their design and performance. Its propulsion efficiency and life span govern the overall performance of a degradable metallic micromotor. Here we review the design and recent advancements of metallic degradable micromotors. Furthermore, we describe the controlled degradation, efficient in vivo drug delivery, and built-in acid neutralization capabilities of degradable micromotors with versatile biomedical applications. Moreover, we discuss micromotors' efficacy in detecting and destroying environmental pollutants. Finally, we address the limitations and future research directions of degradable metallic micromotors.

Untethered Micro/Nanorobots for Remote Sensing: Toward Intelligent Platform

Untethered micro/nanorobots that can wirelessly control their motion and deformation state have gained enormous interest in remote sensing applications due to their unique motion characteristics in various media and diverse functionalities. Researchers are developing micro/nanorobots as innovative tools to improve sensing performance and miniaturize sensing systems, enabling in situ detection of substances that traditional sensing methods struggle to achieve. Over the past decade of development, significant research progress has been made in designing sensing strategies based on micro/nanorobots, employing various coordinated control and sensing approaches. This review summarizes the latest developments on micro/nanorobots for remote sensing applications by utilizing the self-generated signals of the robots, robot behavior, microrobotic manipulation, and robot-environment interactions. Providing recent studies and relevant applications in remote sensing, we also discuss the challenges and future perspectives facing micro/nanorobots-based intelligent sensing platforms to achieve sensing in complex environments, translating lab research achievements into widespread real applications.

Biocatalytic Buoyancy-Driven Nanobots for Autonomous Cell Recognition and Enrichment

Autonomously self-propelled nanoswimmers represent the next-generation nano-devices for bio- and environmental technology. However, current nanoswimmers generate limited energy output and can only move in short distances and duration, thus are struggling to be applied in practical challenges, such as living cell transportation. Here, we describe the construction of biodegradable metal-organic framework based nanobots with chemically driven buoyancy to achieve highly efficient, long-distance, directional vertical motion to "find-and-fetch" target cells. Nanobots surface-functionalized with antibodies against the cell surface marker carcinoembryonic antigen are exploited to impart the nanobots with specific cell targeting capacity to recognize and separate cancer cells. We demonstrate that the self-propelled motility of the nanobots can sufficiently transport the recognized cells autonomously, and the separated cells can be easily collected with a customized glass column, and finally regain their full metabolic potential after the separation. The utilization of nanobots with easy synthetic pathway shows considerable promise in cell recognition, separation, and enrichment.

Strategies in design of self-propelling hybrid micro/nanobots for bioengineering applications

Micro/nanobots are integrated devices developed from engineered nanomaterials that have evolved significantly over the past decades. They can potentially be pre-programmed to operate robustly at numerous hard-to-reach organ/tissues/cellular sites for multiple bioengineering applications such as early disease diagnosis, precision surgeries, targeted drug delivery, cancer therapeutics, bio-imaging, biomolecules isolation, detoxification, bio-sensing, and clearing up clogged arteries with high soaring effectiveness and minimal exhaustion of power. Several techniques have been introduced in recent years to develop programmable, biocompatible, and energy-efficient micro/nanobots. Therefore, the primary focus of most of these techniques is to develop hybrid micro/nanobots that are an optimized combination of purely synthetic or biodegradable bots suitable for the execution of user-defined tasks more precisely and efficiently. Recent progress has been illustrated here as an overview of a few of the achievable construction principles to be used to make biomedical micro/nanobots and explores the pivotal ventures of nanotechnology-moderated development of catalytic autonomous bots. Furthermore, it is also foregrounding their advancement offering an insight into the recent trends and subsequent prospects, opportunities, and challenges involved in the accomplishments of the effective multifarious bioengineering applications.

Sideways propelled bimetallic rods at the water/oil interface

The motion of self-propelling microswimmers is significantly affected by confinement, which can enhance or reduce their mobility and also steer the direction of their propulsion. While their interactions with solid boundaries have already received considerable attention, many aspects of the influence of liquid-liquid interfaces (LLI) on active particle propulsion still remain unexplored. In this work, we studied the adsorption and motion of bimetallic Janus sideways propelled rods dispersed at the interface between an aqueous solution of hydrogen peroxide and oil. The wetting properties of the bimetallic rods result in a wide distribution of their velocities at the LLI. While a fraction of rods remain immotile, we note a significant enhancement of motility for the rest of the particles with velocities of up to 8 times higher in comparison to those observed near a solid wall. Liquid-liquid interfaces, therefore, can provide a new way to regulate the propulsion of bimetallic particles.

Micro-/nanoscale robotics for chemical and biological sensing

The field of micro-/nanorobotics has attracted extensive interest from a variety of research communities and witnessed enormous progress in a broad array of applications ranging from basic research to global healthcare and to environmental remediation and protection. In particular, micro-/nanoscale robots provide an enabling platform for the development of next-generation chemical and biological sensing modalities, owing to their unique advantages as programmable, self-sustainable, and/or autonomous mobile carriers to accommodate and promote physical and chemical processes. In this review, we intend to provide an overview of the state-of-the-art development in this area and share our perspective in the future trend. This review starts with a general introduction of micro-/nanorobotics and the commonly used methods for propulsion of micro-/nanorobots in solution, along with the commonly used methods in their fabrication. Next, we comprehensively summarize the current status of the micro/nanorobotic research in relevance to chemical and biological sensing (e.g., motion-based sensing, optical sensing, and electrochemical sensing). Following that, we provide an overview of the primary challenges currently faced in the micro-/nanorobotic research. Finally, we conclude this review by providing our perspective detailing the future application of soft robotics in chemical and biological sensing.

Chemical Approaches for the Preparation of Bacteria - Nano/Microparticle Hybrid Systems

Bacteria represent a class of living cells that are very attractive carriers for the transport and delivery of nano- and microsized particles. The use of cell-based carriers, such as for example bacteria, may allow to precisely direct nano- or microsized cargo to a desired site, which would greatly enhance the selectivity of drug delivery and allow to mitigate side effects. One key step towards the use of such nano-/microparticle - bacteria hybrids is the immobilization of the cargo on the bacterial cell surface. To fabricate bacteria - nano-/microparticle biohybrid microsystems, a wide range of chemical approaches are available that can be used to immobilize the particle payload on the bacterial cell surface. This article presents an overview of the various covalent and noncovalent chemistries that are available for the preparation of bacteria - nano-/microparticle hybrids. For each of the different chemical approaches, an overview will be presented that lists the bacterial strains that have been modified, the type and size of nanoparticles that have been immobilized, as well as the methods that have been used to characterize the nanoparticle-modified bacteria.

Unidirectional rotation of micromotors on water powered by pH-controlled disassembly of chiral molecular crystals

Biological and synthetic molecular motors, fueled by various physical and chemical means, can perform asymmetric linear and rotary motions that are inherently related to their asymmetric shapes. Here, we describe silver-organic micro-complexes of random shapes that exhibit macroscopic unidirectional rotation on water surface through the asymmetric release of cinchonine or cinchonidine chiral molecules from their crystallites asymmetrically adsorbed on the complex surfaces. Computational modeling indicates that the motor rotation is driven by a pH-controlled asymmetric jet-like Coulombic ejection of chiral molecules upon their protonation in water. The motor is capable of towing very large cargo, and its rotation can be accelerated by adding reducing agents to the water.

Medical micro- and nanomotors in the body

Attributed to the miniaturized body size and active mobility, micro- and nanomotors (MNMs) have demonstrated tremendous potential for medical applications. However, from bench to bedside, massive efforts are needed to address critical issues, such as cost-effective fabrication, on-demand integration of multiple functions, biocompatibility, biodegradability, controlled propulsion and in vivo navigation. Herein, we summarize the advances of biomedical MNMs reported in the past two decades, with particular emphasis on the design, fabrication, propulsion, navigation, and the abilities of biological barriers penetration, biosensing, diagnosis, minimally invasive surgery and targeted cargo delivery. Future perspectives and challenges are discussed as well. This review can lay the foundation for the future direction of medical MNMs, pushing one step forward on the road to achieving practical theranostics using MNMs.

Swarming Magnetic Microrobots for Pathogen Isolation from Milk

Bovine mastitis produced by Staphylococcus aureus (S. aureus) causes major problems in milk production due to the staphylococcal enterotoxins produced by this bacterium. These enterotoxins are stable and cannot be eradicated easily by common hygienic procedures once they are formed in dairy products. Here, magnetic microrobots (MagRobots) are developed based on paramagnetic hybrid microstructures loaded with IgG from rabbit serum that can bind and isolate S. aureus from milk in a concentration of 3.42 10⁴ CFU g^-1 (allowable minimum level established by the United States Food and Drug Administration, FDA). Protein A, which is present on the cell wall of S. aureus, selectively binds IgG from rabbit serum and loads the bacteria onto the surface of the MagRobots. The selective isolation of S. aureus is confirmed using a mixed suspension of S. aureus and Escherichia coli (E. coli). Moreover, this fuel-free system based on magnetic robots does not affect the natural milk microbiota or add any toxic compound resulting from fuel catalysis. This system can be used to isolate and transport efficiently S. aureus and discriminate it from nontarget bacteria for subsequent identification. Finally, this system can be scaled up for industrial use in food production.

Magnetic Nanoseparation Technology for Efficient Control of Microorganisms and Toxins in Foods: A Review

Outbreaks of foodborne diseases mediated by food microorganisms and toxins remain one of the leading causes of disease and death worldwide. It not only poses a serious threat to human health and safety but also imposes a huge burden on health care and socioeconomics. Traditional methods for the removal and detection of pathogenic bacteria and toxins in various samples such as food and drinking water have certain limitations, requiring a rapid and sensitive strategy for the enrichment and separation of target analytes. Magnetic nanoparticles (MNPs) exhibit excellent performance in this field due to their fascinating properties. The strategy of combining biorecognition elements with MNPs can be used for fast and efficient enrichment and isolation of pathogens. In this review, we describe new trends and practical applications of magnetic nanoseparation technology in the detection of foodborne microorganisms and toxins. We mainly summarize the biochemical modification and functionalization methods of commonly used magnetic nanomaterial carriers and discuss the application of magnetic separation combined with other instrumental analysis techniques. Combined with various detection techniques, it will increase the efficiency of detection and identification of microorganisms and toxins in rapid assays.

Multifunctional Composite Hydrogels for Bacterial Capture, Growth/Elimination, and Sensing Applications

Hydrogels are cross-linked networks of hydrophilic polymer chains with a three-dimensional structure. Owing to their unique features, the application of hydrogels for bacterial/antibacterial studies and bacterial infection management has grown in importance in recent years. This trend is likely to continue due to the rise in bacterial infections and antimicrobial resistance. By exploiting their physicochemical characteristics and inherent nature, hydrogels have been developed to achieve bacterial capture and detection, bacterial growth or elimination, antibiotic delivery, or bacterial sensing. Traditionally, the development of hydrogels for bacterial/antibacterial studies has focused on achieving a single function such as antibiotic delivery, antibacterial activity, bacterial growth, or bacterial detection. However, recent studies demonstrate the fabrication of multifunctional hydrogels, where a single hydrogel is capable of performing more than one bacterial/antibacterial function, or composite hydrogels consisting of a number of single functionalized hydrogels, which exhibit bacterial/antibacterial function synergistically. In this review, we first highlight the hydrogel features critical for bacterial studies and infection management. Then, we specifically address unique hydrogel properties, their surface/network functionalization, and their mode of action for bacterial capture, adhesion/growth, antibacterial activity, and bacterial sensing, respectively. Finally, we provide insights into different strategies for developing multifunctional hydrogels and how such systems can help tackle, manage, and understand bacterial infections and antimicrobial resistance. We also note that the strategies highlighted in this review can be adapted to other cell types and are therefore likely to find applications beyond the field of microbiology.

In situ preparation of glyco-micromotors and their bacteria loading/guiding ability

We successfully synthesized glyco-micromotors in situ directed by multifunctional glycopolymers, which were obtained by copolymerizing 2-methacrylamido glucopyranose (MAG) and 2-(diethylamino)ethyl methacrylate (DEAEMA) monomers. The fabricated glyco-micromotors present abilities in loading and guiding bacteria with different individual and group motions.

Micro/nanomotor technology: the new era for food safety control

Food poisoning caused by eating contaminated food remains a threat to global public health. Making the situation even worse is the aggravated global environmental pollution, which poses a major threat to the safety of agricultural resources. Food adulteration has been rampant owing to negligent national food safety regulations. The speed at which contaminated food is detected and disposed of determines the extent to which consumers' lives are safeguarded and agricultural economic losses are prevented. Micro/nanomotors offer a high-speed mobile loading platform that substantially increases the chemical reaction rates and, accordingly, exhibit great potential as alternatives to conventional detection and degradation techniques. This review summarizes the propulsion modes applicable to micro/nanomotors in food systems and the advantages of using micro/nanomotors, highlighting examples of their potential use in recent years for the detection and removal of food contaminants. Micro/nanomotors are an emerging technology for food applications that is moving toward mass production, simple preparation, and important functions.

Biocompatible micromotors for biosensing

Micro/nanomotors are nanoscale devices that have been explored in various fields, such as drug delivery, environmental remediation, or biosensing and diagnosis. The use of micro/nanomotors has grown considerably over the past few years, partially because of the advantages that they offer in the development of new conceptual avenues in biosensing. This is due to their propulsion and intermixing in solution compared with their respective static forms, which enables motion-based detection methods and/or decreases bioassay time. This review focuses on the impacts of micro/nanomotors on biosensing research in the last 2 years. An overview of designs for bioreceptor attachment to micro/nanomotors is given. Recent developments have focused on chemically propelled micromotors using external fuels, commonly hydrogen peroxide. However, the associated fuel toxicity and inconvenience of use in relevant biological samples such as blood have prompted researchers to explore new micro/nanomotor biosensing approaches based on biocompatible propulsion sources such as magnetic or ultrasound fields. The main advances in biocompatible propulsion sources for micro/nanomotors as novel biosensing platforms are discussed and grouped by their propulsion-driven forces. The relevant analytical applications are discussed and representatively illustrated. Moreover, envisioning future biosensing applications, the principal advantages of micro/nanomotor synthesis using biocompatible and biodegradable materials are given. The review concludes with a realistic drawing on the present and future perspectives.

Shape-Encoded Functional Hydrogel Pellets for Multiplexed Detection of Pathogenic Bacteria Using a Gas Pressure Sensor

Gas pressure is a promising signal readout mode in point-of-care testing for its merits such as rapidity, simplicity, affordability, and no need for sophisticated instrumentation. Herein, a gas pressure sensor for multiplexed detection of pathogenic bacteria was developed on a hydrogel platform. Spherical and square hydrogel pellets prepared by cross-linking of sodium alginate were functionalized with nisin and ConA for the capture of Staphylococcus aureus and Escherichia coli O157:H7, respectively. By using the shape-encoded functional hydrogel pellets and aptamer-modified platinum-coated gold nanoparticles (Au@PtNPs), a dual-molecule recognition mode was established for rapid and specific detection of the two pathogenic bacteria. Au@PtNPs were applied as signal probes to efficiently catalyze the decomposition of H₂O₂ for generating abundant O₂, which was converted into an amplified gas pressure signal. In two closed containers, the significant gas pressure signals were monitored with a portable pressure meter to quantitate the two pathogenic bacteria. The sensor was successfully applied to detect the pathogenic bacteria in various environmental, biological, and food samples. Thus, the proof-of-principle work paves a new avenue for multiplexed detection of pathogenic bacteria with shape-encoded hydrogel pellets combined with gas pressure signal readout.

Precisely controlled and deeply penetrated micro-nano hybrid multifunctional motors with enhanced antibacterial activity against refractory biofilm infections

The biofilm resistance of microorganisms has severe economic and environmental implications, especially the contamination of facilities associated with human life, including medical implants, air-conditioning systems, water supply systems, and food-processing equipment, resulting in the prevalence of infectious diseases. Once bacteria form biofilms, their antibiotic resistance can increase by 10-1,000-fold, posing a great challenge to the treatment of related diseases. In order to overcome the contamination of bacterial biofilm, destroying the biofilm's matrix so as to solve the penetration depth dilemma of antibacterial agents is the most effective way. Here, a magnetically controlled multifunctional micromotor was developed by using H₂O₂ as the fuel and MnO₂ as the catalyst to treat bacterial biofilm infection. In the presence of H₂O₂, the as-prepared motors could be self-propelled by the generated oxygen microbubbles. Thereby, the remotely controlled motors could drill into the EPS of biofilm and disrupt them completely with the help of bubbles. Finally, the generated highly toxic •OH could efficiently kill the unprotected bacteria. This strategy combined the mechanical damage, highly toxic •OH, and precise magnetic guidance in one system, which could effectively eliminate biologically infectious fouling in microchannels within 10 min, possessing a wide range of practical application prospects especially in large scale and complex infection sites.

Contemporary Tools for the Cure against Pernicious Microorganisms: Micro-/Nanorobots

One of the most pressing concerns to global public health is the emergence of drug-resistant pathogenic microorganisms due to increased unconscious antibiotic usage. With the rising antibiotic resistance, existing antimicrobial agents lose their effectiveness over time. This indicates that newer and more effective antimicrobial agents and methods should be investigated. Many studies have shown that micro-/nanorobots exhibit promise in the treatment of microbial infections with their great properties, such as the intrinsic antimicrobial activities owing to their oxidative stress induction and metal ion release capabilities, and effective and autonomous delivery of antibiotics to the target area. In addition, they have multiple simultaneous mechanisms of action against microbes, which makes them remarkable in antimicrobial activity. This review focuses on the antimicrobial micro-/nanorobots and their strategies to impede biofilm formation, following a brief introduction of the latest advancements in micro-/nanorobots, and their implementations against various bacteria, and other microorganisms.

Enzyme-Powered Hollow Nanorobots for Active Microsampling Enabled by Thermoresponsive Polymer Gating

Achieving molecular sample capture at micro/nanoscales while integrating functions of controllable loading and real-time monitoring of cargo molecules is of great significance in the development of intelligent micro/nanorobots. Herein, we prepare a temperature-responsive microsampling nanorobot by encapsulating metal (Au) nanodots inside hollow mesoporous silica nanoparticles and grafting a temperature-responsive polymer, poly(N-isopropylacrylamide), on their external surface. The molecular gate of nanochannels accessing the internal hollow reservoir can be switched between "open" and "closed" states by regulating the temperature, allowing on-demand loading and releasing of small molecules. The internally embedded surface-enhanced Raman scattering hotspots of gold nanodots can serve as sensing probes for real-time detection of the molecular cargo load inside the hollow nanorobots. Furthermore, we demonstrate temperature-dependent self-propulsion behavior of the nanorobots driven by enzymatic reactions. The active motion behavior can favorably regulate the loading efficiency of molecular cargos. In addition, by further introducing the magnetic component Ni, the nanorobots can accomplish effective transportation of cargo molecules by magnetic guidance under real-time Raman monitoring. The current strategy is expected to provide a manipulable nanorobot platform for precise biomedical sampling, which holds promising potential for disease diagnosis or controlled drug delivery in precision medicine.

Quantitative Analysis of Drag Force for Task-Specific Micromachine at Low Reynolds Numbers

Micromotors have spread widely in order to meet the needs of new applications, including cell operation, drug delivery, biosensing, precise surgery and environmental decontamination, due to their small size, low energy consumption and large propelling power, especially the newly designed multifunctional micromotors that combine many extra shape features in one device. Features such as rod-like receptors, dendritic biosensors and ball-like catalyzing enzymes are added to the outer surface of the tubular micromotor during fabrication to perform their special mission. However, the structural optimization of motion performance is still unclear. The main factor restricting the motion performance of the micromotors is the drag forces. The complex geometry of a micromotor makes its dynamic behavior more complicated in a fluid environment. This study aimed to design the optimum structure of tubular micromotors with minimum drag forces and obtain the magnitude of drag forces considering both the internal and external fluids of the micromotors. By using the computational fluid dynamics software Fluent 18.0 (ANSYS), the drag force and the drag coefficient of different conical micromotors were calculated. Moreover, the influence of the Reynolds numbers Re, the semi-cone angle δ and the ratios ξ and η on the drag coefficient was analyzed. The results show the drag force monotonically increased with Reynolds numbers Re and the ratio η. The extreme point of the drag curve is reached when the semi-cone angle δ is 8° and the ratio ξ is 3.846. This work provides theoretical support and guidance for optimizing the design and development of conical micromotors.

Micromotor-in-Sponge Platform for Multicycle Large-Volume Degradation of Organic Pollutants

The presence of organic pollutants in the environment is a global threat to human health and ecosystems due to their bioaccumulation and long-term persistence. Hereby a micromotor-in-sponge concept is presented that aims not only at pollutant removal, but towards an efficient in situ degradation by exploiting the synergy between the sponge hydrophobic nature and the rapid pollutant degradation promoted by the cobalt-ferrite (CFO) micromotors embedded at the sponge's core. Such a platform allows the use of extremely low fuel concentration (0.13% H₂ O₂ ), as well as its reusability and easy recovery. Moreover, the authors demonstrate an efficient multicycle pollutant degradation and treatment of large volumes (1 L in 15 min) by using multiple sponges. Such a fast degradation process is due to the CFO bubble-propulsion motion mechanism, which induces both an enhanced fluid mixing within the sponge and an outward flow that allows a rapid fluid exchange. Also, the magnetic control of the system is demonstrated, guiding the sponge position during the degradation process. The micromotor-in-sponge configuration can be extrapolated to other catalytic micromotors, establishing an alternative platform for an easier implementation and recovery of micromotors in real environmental applications.

Micro-/Nanorobots in Antimicrobial Applications: Recent Progress, Challenges, and Opportunities

The evolution of drug-resistant pathogenic bacteria remains one of the most urgent threats to public health worldwide. Even worse, the bacterial cells commonly form biofilms through aggregation and adhesion, preventing antibiotic penetration and resisting environmental stress. Moreover, biofilms tend to grow in some hard-to-reach regions, bringing difficulty for antibiotic delivery at the infected site. The drug-resistant pathogenic bacteria and intractable biofilm give rise to chronic and recurrent infections, exacerbating the challenge in combating bacterial infections. Micro/nanorobots (MNRs) are capable of active cargo delivery, targeted treatment with high precision, and motion-assisted mechanical force, which enable transport and enhance penetration of antibacterial agents into the targeted site, thus showing great promise in emerging as an attractive alternative to conventional antibacterial therapies. This review summarizes the recent advances in micro-/nanorobots for antibacterial applications, with emphasis on those novel strategies for drug-resistance bacterium and stubborn biofilm infections. Insights on the future development of MNRs with good functionality and biosafety offer promising approaches to address infections in the clinic setting.

Self-assembled plasmonic nanoarrays for enhanced bacterial identification and discrimination

The rapid and accurate bacterial testing is a critical step for the management of infectious diseases, but challenges remain largely due to a lack of advanced sensing tools. Here we report the development of highly plasmon-active, biofunctional nanoparticle arrays for simultaneous capture, identification, and differentiation of bacteria by surface-enhanced Raman scattering (SERS). The nanoarrays were facilely prepared through an electrostatic mechanism-controlled self-assembly of metallic nanoparticles at liquid-liquid interfaces, and exhibited high SERS sensitivity beyond femtomole, good reproducibility (relative standard deviation of 2.7%) and stability. Modification of the nanoarrays with concanavalin A allowed to effective capture of both Gram-positive and Gram-negative bacteria (bacterial-capture efficiency maintained beyond 50%) at bacterial concentrations ranging from 50 to 2000 CFU mL^-1, as determined by the plate-counting method. Moreover, single-cell Raman fingerprinting and discrimination of eight different bacteria species with high signal-to-noise ratio, excellent spectral reproducibility, and a total assay time of 1.5 h was achieved under fairly mild conditions (24 μW, acquisition time: 1 s). Collectively, we believe that our biofunctionalized, SERS-based self-assembled nanoarrays have great potential to help in rapid and label-free bacterial diagnosis and phenotyping study.

Untethered Microrobots for Active Drug Delivery: From Rational Design to Clinical Settings

Recent advances of untethered microrobots, which navigate the complex regions in vivo for therapeutics, have presented promising multiple applications on future healthcare. Microrobots used for active drug delivery system (DDS) have been demonstrated for advanced targeting distribution, improved delivery efficiency, and reduced systemic side effects. In this review, the therapeutic benefits of active DDS are presented compared to the traditional passive DDS, which illustrate the historical reasons for choosing active DDS. An integrated 5D radar chart analysis model containing the core capabilities of the active DDS is innovatively proposed. It would be a practical tool for measurement and mapping of the field of active delivery, followed by the evolutions and bottlenecks of each technical module. The comprehensive consideration of microrobots before clinical application is also discussed from the aspects of robot ethics, dosage, quality control and stability control in actual production. Gastrointestinal and blood administration, as two major clinical scenes of drug delivery, are discussed in detail as examples of the potential bedside applications of active DDS. Finally, combined with the reported analysis model, the current status and future outlook from the translation prospect to the clinical scenes of microrobots are provided.

Core-Shell Structured Micro-Nanomotors: Construction, Shell Functionalization, Applications, and Perspectives

The successful integration of well-designed micro-nanomotors (MNMs) with diverse functional systems, such as, living systems, remote actuation systems, intelligent sensors, and sensing systems, offers many opportunities to not only endow them with diverse functionalization interfaces but also bring augmented or new properties in a wide variety of applications. Core-shell structured MNM systems have been considered to play an important role in a wide range of applications as they provide a platform to integrate multiple complementary components via decoration, encapsulation, or functionalization into a single functional system, being able to protect the active species from harsh environments, and bring improved propulsion performance, stability, non-toxicity, multi-functionality, and dispersibility, etc., which are not easily available from the isolated components. More importantly, the hetero-interfaces between individual components within a core-shell structure might give rise to boosted or new physiochemical properties. This review will bring together these key aspects of the core-shell structured MNMs, ranging from advanced protocols, enhanced/novel functionalities arising from diverse functional shells, to integrated core-shell structured MNMs for diverse applications. Finally, current challenges and future perspectives for the development of core-shell structured MNMs are discussed in term of synthesis, functions, propulsions, and applications.

Cooperative transport by flocking phototactic micromotors

Cargo delivery by micro/nanomotors provides enormous opportunities for micromanipulation, environmental cleaning, drug delivery, etc. However, due to the limited driving force, it is usually difficult for single micro/nanomotors to transport cargoes much larger or heavier than themselves. Here, we demonstrate that flocking phototactic TiO2 micromotors can cooperatively transport multiple and different types of large cargoes based on light-responsive diffusiophoresis. Utilizing spontaneous diffusiophoretic attraction, flocking TiO2 micromotors can load large cargoes. Under UV light navigation, flocking TiO2 micromotors cooperatively carry and transport cargoes via collective diffusiophoretic repulsion in open space or complex microenvironments. After reaching the destination, the carried cargoes can also be unloaded from the flock and be deployed at a predetermined destination by disassembling or reversing the flock. This study may pave the way for developing intelligent swarming micro/nanorobots for cooperative targeting micromanipulation and advancing their applications in drug delivery and microengineering.

Polymeric Micro/Nanomotors and Their Biomedical Applications

Since their naissance in the 2000s, various micro or nanomotors with powerful functions have been proposed. Among them, polymer-based micro or nanomotors stand out for the easy processing and facile functionalization, holding immense potential for bioapplications. In this review, fabrication of polymer-based micro or nanomotors and their applications in biomedical areas are covered. Classic manufacturing approaches as well as cutting-edge techniques are discussed with representative works highlighted. Current challenges and future prospects are presented in the hope of pointing new research directions to facilitate practical translations of micro/nanomotors.

Microfluidics for Microswimmers: Engineering Novel Swimmers and Constructing Swimming Lanes on the Microscale, a Tutorial Review

This paper provides an updated review of recent advances in microfluidics applied to artificial and biohybrid microswimmers. Sharing the common regime of low Reynolds number, the two fields have been brought together to take advantage of the fluid characteristics at the microscale, benefitting microswimmer research multifold. First, microfluidics offer simple and relatively low-cost devices for high-fidelity production of microswimmers made of organic and inorganic materials in a variety of shapes and sizes. Microscale confinement and the corresponding fluid properties have demonstrated differential microswimmer behaviors in microchannels or in the presence of various types of physical or chemical stimuli. Custom environments to study these behaviors have been designed in large part with the help of microfluidics. Evaluating microswimmers in increasingly complex lab environments such as microfluidic systems can ensure more effective implementation for in-field applications. The benefits of microfluidics for the fabrication and evaluation of microswimmers are balanced by the potential use of microswimmers for sample manipulation and processing in microfluidic systems, a large obstacle in diagnostic and other testing platforms. In this review various ways in which these two complementary technology fields will enhance microswimmer development and implementation in various fields are introduced.

Engineering Active Micro and Nanomotors

Micro- and nanomotors (MNMs) are micro/nanoparticles that can perform autonomous motion in complex fluids driven by different power sources. They have been attracting increasing attention due to their great potential in a variety of applications ranging from environmental science to biomedical engineering. Over the past decades, this field has evolved rapidly, with many significant innovations contributed by global researchers. In this review, we first briefly overview the methods used to propel motors and then present the main strategies used to design proper MNMs. Next, we highlight recent fascinating applications of MNMs in two examplary fields, water remediation and biomedical microrobots, and conclude this review with a brief discussion of challenges in the field.

Scallop Theorem and Swimming at the Mesoscale

By comparing theoretical modeling, simulations, and experiments, we show that there exists a swimming regime at low Reynolds numbers solely driven by the inertia of the swimmer itself. This is demonstrated by considering a dumbbell with an asymmetry in coasting time in its two spheres. Despite deforming in a reciprocal fashion, the dumbbell swims by generating a nonreciprocal Stokesian flow, which arises from the asymmetry in coasting times. This asymmetry acts as a second degree of freedom, which allows the scallop theorem to be fulfilled at the mesoscopic scale.

Interactions between Biomedical Micro-/Nano-Motors and the Immune Molecules, Immune Cells, and the Immune System: Challenges and Opportunities

Mobile micro- and nano-motors (MNMs) emerge as revolutionary platforms for biomedical applications, including drug delivery, biosensing, non-invasive surgery, and cancer therapy. While for applications in biomedical fields and practical clinical translation, the interactions of these untethered tiny machines with the immune system is an essential issue to be considered. This review highlights the recent approaches of surpassing immune barriers to prevent foreign motors from triggering immune responses. In addition to trials focusing on the function preservation of MNMs, examples of versatile MNMs working with the immune components (immune molecules, immune cells and the whole system) to achieve cancer immunotherapy, immunoassay, and detoxification are outlined. The immune interference part provides researchers an idea about what is the limit presented by the immune components. The coworking part suggests ways to bypass or even utilize the limit. With interdisciplinary cooperation of nanoengineering, materials science, and immunology field, the rationally designed functional MNMs are expected to provide novel opportunities for the biomedical field.

'Sweeping rods': cargo transport by self-propelled bimetallic microrods moving perpendicular to their long axis

A possible application of self-propelling particles is the transport of microscopic cargo. Maximizing the collection and transport efficiency of particulate matter requires the area swept by the moving particle to be as large as possible. One such particle geometry are rods propelled perpendicular to their long axis, that act as "sweepers" for collecting particles. Here we report on the required Janus coating to achieve such motion, and on the dynamics of the collection and transport of microscopic cargo by sideways propelled Janus rods.

3D printing of functional microrobots

3D printing (also called "additive manufacturing" or "rapid prototyping") is able to translate computer-aided and designed virtual 3D models into 3D tangible constructs/objects through a layer-by-layer deposition approach. Since its introduction, 3D printing has aroused enormous interest among researchers and engineers to understand the fabrication process and composition-structure-property correlation of printed 3D objects and unleash its great potential for application in a variety of industrial sectors. Because of its unique technological advantages, 3D printing can definitely benefit the field of microrobotics and advance the design and development of functional microrobots in a customized manner. This review aims to present a generic overview of 3D printing for functional microrobots. The most applicable 3D printing techniques, with a focus on laser-based printing, are introduced for the 3D microfabrication of microrobots. 3D-printable materials for fabricating microrobots are reviewed in detail, including photopolymers, photo-crosslinkable hydrogels, and cell-laden hydrogels. The representative applications of 3D-printed microrobots with rational designs heretofore give evidence of how these printed microrobots are being exploited in the medical, environmental, and other relevant fields. A future outlook on the 3D printing of microrobots is also provided.

A Magnetically Guided Self-Rolled Microrobot for Targeted Drug Delivery, Real-Time X-Ray Imaging, and Microrobot Retrieval

Targeted drug delivery using a microrobot is a promising technique capable of overcoming the limitations of conventional chemotherapy that relies on body circulation. However, most studies of microrobots used for drug delivery have only demonstrated simple mobility rather than precise targeting methods and prove the possibility of biodegradation of implanted microrobots after drug delivery. In this study, magnetically guided self-rolled microrobot that enables autonomous navigation-based targeted drug delivery, real-time X-ray imaging, and microrobot retrieval is proposed. The microrobot, composed of a self-rolled body that is printed using focused light and a surface with magnetic nanoparticles attached, demonstrates the loading of doxorubicin and an X-ray contrast agent for cancer therapy and X-ray imaging. The microrobot is precisely mobilized to the lesion site through automated targeting using magnetic field control of an electromagnetic actuation system under real-time X-ray imaging. The photothermal effect using near-infrared light reveals rapid drug release of the microrobot located at the lesion site. After drug delivery, the microrobot is recovered without potential toxicity by implantation or degradation using a magnetic-field-switchable coiled catheter. This microrobotic approach using automated control method of the therapeutic agents-loaded microrobot has potential use in precise localized drug delivery systems.

Capture and detection of urine bacteria using a microchannel silicon nanowire microfluidic chip coupled with MALDI-TOF MS

Fast bacterial identification in urine samples was achieved by capturing bacteria on a microchannel silicon nanowire microfluidic chip, followed by MALDI-TOF MS detection. Under the optimized conditions, bacteria with a concentration of 106 CFU mL-1 in urine samples could be identified without culture. If cultured for 4 hours, bacteria with a concentration as low as 103 CFU mL-1 were identified.

Gold Nanoparticles: Can They Be the Next Magic Bullet for Multidrug-Resistant Bacteria?

In 2017 the World Health Organization (WHO) announced a list of the 12 multidrug-resistant (MDR) families of bacteria that pose the greatest threat to human health, and recommended that new measures should be taken to promote the development of new therapies against these superbugs. Few antibiotics have been developed in the last two decades. Part of this slow progression can be attributed to the surge in the resistance acquired by bacteria, which is holding back pharma companies from taking the risk to invest in new antibiotic entities. With limited antibiotic options and an escalating bacterial resistance there is an urgent need to explore alternative ways of meeting this global challenge. The field of medical nanotechnology has emerged as an innovative and a powerful tool for treating some of the most complicated health conditions. Different inorganic nanomaterials including gold, silver, and others have showed potential antibacterial efficacies. Interestingly, gold nanoparticles (AuNPs) have gained specific attention, due to their biocompatibility, ease of surface functionalization, and their optical properties. In this review, we will focus on the latest research, done in the field of antibacterial gold nanoparticles; by discussing the mechanisms of action, antibacterial efficacies, and future implementations of these innovative antibacterial systems.

Trends in Micro-/Nanorobotics: Materials Development, Actuation, Localization, and System Integration for Biomedical Applications

Micro-/nanorobots (m-bots) have attracted significant interest due to their suitability for applications in biomedical engineering and environmental remediation. Particularly, their applications in in vivo diagnosis and intervention have been the focus of extensive research in recent years with various clinical imaging techniques being applied for localization and tracking. The successful integration of well-designed m-bots with surface functionalization, remote actuation systems, and imaging techniques becomes the crucial step toward biomedical applications, especially for the in vivo uses. This review thus addresses four different aspects of biomedical m-bots: design/fabrication, functionalization, actuation, and localization. The biomedical applications of the m-bots in diagnosis, sensing, microsurgery, targeted drug/cell delivery, thrombus ablation, and wound healing are reviewed from these viewpoints. The developed biomedical m-bot systems are comprehensively compared and evaluated based on their characteristics. The current challenges and the directions of future research in this field are summarized.

Sense–Analyze–Respond–Actuate (SARA) Paradigm: Proof of Concept System Spanning Nanoscale and Macroscale Actuation for Detection of Escherichia coli in Aqueous Media

Foodborne pathogens are a major concern for public health. We demonstrate for the first time a partially automated sensing system for rapid (~17 min), label-free impedimetric detection of Escherichia coli spp. in food samples (vegetable broth) and hydroponic media (aeroponic lettuce system) based on temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm) nanobrushes. This proof of concept (PoC) for the Sense-Analyze-Respond-Actuate (SARA) paradigm uses a biomimetic nanostructure that is analyzed and actuated with a smartphone. The bio-inspired soft material and sensing mechanism is inspired by binary symbiotic systems found in nature, where low concentrations of bacteria are captured from complex matrices by brush actuation driven by concentration gradients at the tissue surface. To mimic this natural actuation system, carbon-metal nanohybrid sensors were fabricated as the transducer layer, and coated with PNIPAAm nanobrushes. The most effective coating and actuation protocol for E. coli detection at various temperatures above/below the critical solution temperature of PNIPAAm was determined using a series of electrochemical experiments. After analyzing nanobrush actuation in stagnant media, we developed a flow through system using a series of pumps that are triggered by electrochemical events at the surface of the biosensor. SARA PoC may be viewed as a cyber-physical system that actuates nanomaterials using smartphone-based electroanalytical testing of samples. This study demonstrates thermal actuation of polymer nanobrushes to detect (sense) bacteria using a cyber-physical systems (CPS) approach. This PoC may catalyze the development of smart sensors capable of actuation at the nanoscale (stimulus-response polymer) and macroscale (non-microfluidic pumping).

Controllable and Continuous Hollow Fiber Swimmers Based on the Marangoni Effect

The rapid response movement caused by the Marangoni effect, a surface tension gradient-induced mass transfer behavior, has spurred considerable promise for diverse applications from microrobots and microreactors to smart drug delivery. Herein, we fabricated an aligned hollow fiber swimmer that showed self-propel movement on a water surface based on the Marangoni effect. By rational designing of an aligned hollow microstructure and an optimized geometrical shape, this swimmer can move continuously for more than 600 s and the maximum angular velocity can reach 22 rad·s^-1. The movement process of the swimmer is clearly monitored by infrared imaging and the process fluid migration. Moreover, this swimmer exhibited a highly controllable motion mode induced by a magnetic field and a concentration gradient. We designed a novel continuous motion system under the heat conversion from solar energy illumination into mechanical energy. This swimmer shows potential application prospects in controlled cargo transportation and convenient energy conversion systems.

Medical Micro/Nanorobots in Precision Medicine

Advances in medical robots promise to improve modern medicine and the quality of life. Miniaturization of these robotic platforms has led to numerous applications that leverages precision medicine. In this review, the current trends of medical micro and nanorobotics for therapy, surgery, diagnosis, and medical imaging are discussed. The use of micro and nanorobots in precision medicine still faces technical, regulatory, and market challenges for their widespread use in clinical settings. Nevertheless, recent translations from proof of concept to in vivo studies demonstrate their potential toward precision medicine.

A single-tube sample preparation method based on a dual-electrostatic interaction strategy for molecular diagnosis of gram-negative bacteria

A single-tube method based on a dual-electrostatic interaction (EI) strategy for bacteria capture and DNA extraction was designed to enable the highly sensitive detection of nucleic acids. Specially designed magnetic nanoparticles were developed to meet the opposing requirements of a single-tube method, which exist between the strong EI required for efficient bacteria capture and the weak EI required for DNA extraction with minimal DNA adsorption. A dual-EI strategy for the single-tube (DESIGN) method was thus developed to integrate bacteria enrichment, bacteria cell lysis, and DNA recovery in a single tube, thereby minimizing precious sample loss and reducing handling time. Subsequently, we evaluated the performance with a variety of concentrations from 5 to 100 colony-forming units (CFU)/10 mL human urine and milk samples. The DESIGN method achieved the simple and sensitive detection of Salmonella enterica serovar Typhimurium in 10 mL of human urine and milk samples up to 5 CFU by quantitative PCR. Furthermore, the DESIGN method detected Brucella ovis and Escherichia coli from 10 mL of human urine with a detection limit up to 5 CFU/10 mL. Graphical abstract.