Recent Advances in One-Dimensional Micro/Nanomotors: Fabrication, Propulsion and Application

Due to their tiny size, autonomous motion and functionalize modifications, micro/nanomotors have shown great potential for environmental remediation, biomedicine and micro/nano-engineering. One-dimensional (1D) micro/nanomotors combine the characteristics of anisotropy and large aspect ratio of 1D materials with the advantages of functionalization and autonomous motion of micro/nanomotors for revolutionary applications. In this review, we discuss current research progress on 1D micro/nanomotors, including the fabrication methods, driving mechanisms, and recent advances in environmental remediation and biomedical applications, as well as discuss current challenges and possible solutions. With continuous attention and innovation, the advancement of 1D micro/nanomotors will pave the way for the continued development of the micro/nanomotor field.

Enzyme-powered micro- and nano-motors: key parameters for an application-oriented design

Nature has inspired the creation of artificial micro- and nanomotors that self-propel converting chemical energy into mechanical action. These tiny machines have appeared as promising biomedical tools for treatment and diagnosis and have also been used for environmental, antimicrobial or sensing applications. Among the possible catalytic engines, enzymes have emerged as an alternative to inorganic catalysts due to their biocompatibility and the variety and bioavailability of fuels. Although the field of enzyme-powered micro- and nano-motors has a trajectory of more than a decade, a comprehensive framework on how to rationally design, control and optimize their motion is still missing. With this purpose, herein we performed a thorough bibliographic study on the key parameters governing the propulsion of these enzyme-powered devices, namely the chassis shape, the material composition, the motor size, the enzyme type, the method used to incorporate enzymes, the distribution of the product released, the motion mechanism, the motion media and the technique used for motion detection. In conclusion, from the library of options that each parameter offers there needs to be a rational selection and intelligent design of enzymatic motors based on the specific application envisioned.

Micellar Polymer Magnetic Microrobots as Efficient Nerve Agent Microcleaners

Micro-/nanorobot technology has developed rapidly in recent years due to their great potential to perform multiple tasks. Here, we develop magnetic microrobots prepared as polycaprolactone/Fe₃O₄ microspheres covered by micellar polyethyleneimine and use them to efficiently remove a nerve agent from contaminated water. The magnetic polymeric microrobots presented in this work removed around 60% of the nerve agent from water samples in a short time. The attractive performance of these magnetic microrobots offers a very promising approach to large-scale water treatment for environmental remediation.

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.

Photosensitive Polymeric Janus Micromotor for Enzymatic Activity Protection and Enhanced Substrate Degradation

Immobilizing enzymes into microcarriers is a strategy to improve their long-term stability and reusability, hindered by (UV) light irradiation. However, in such approaches, enzyme-substrate interaction is mediated by diffusion, often at slow kinetics. In contrast, enzyme-linked self-propelled motors can accelerate this interaction, frequently mediated by the convection mechanism. This work reports on a new photosensitive polymeric Janus micromotor (JM) for UV-light protection of enzymatic activity and efficient degradation of substrates accelerated by the JMs. The JMs were assembled with UV-photosensitive modified chitosan, co-encapsulating fluorescent-labeled proteins and enzymes as models and magnetite and platinum nanoparticles for magnetic and catalytic motion. The JMs absorbed UV light, protecting the enzymatic activity and accelerating the enzyme-substrate degradation by magnetic/catalytic motion. Immobilizing proteins in photosensitive JMs is a promising strategy to improve the enzyme's stability and hasten the kinetics of substrate degradation, thereby enhancing the enzymatic process's efficiency.

Oxygen Generation Using Catalytic Nano/Micromotors

Gaseous oxygen plays a vital role in driving the metabolism of living organisms and has multiple agricultural, medical, and technological applications. Different methods have been discovered to produce oxygen, including plants, oxygen concentrators and catalytic reactions. However, many such approaches are relatively expensive, involve challenges, complexities in post-production processes or generate undesired reaction products. Catalytic oxygen generation using hydrogen peroxide is one of the simplest and cleanest methods to produce oxygen in the required quantities. Chemically powered micro/nanomotors, capable of self-propulsion in liquid media, offer convenient and economic platforms for on-the-fly generation of gaseous oxygen on demand. Micromotors have opened up opportunities for controlled oxygen generation and transport under complex conditions, critical medical diagnostics and therapy. Mobile oxygen micro-carriers help better understand the energy transduction efficiencies of micro/nanoscopic active matter by careful selection of catalytic materials, fuel compositions and concentrations, catalyst surface curvatures and catalytic particle size, which opens avenues for controllable oxygen release on the level of a single catalytic microreactor. This review discusses various micro/nanomotor systems capable of functioning as mobile oxygen generators while highlighting their features, efficiencies and application potentials in different fields.

Peroxidase driven micromotors for dynamic bioremediation

Phenolics are size products present in tons concentrations in industrial wastewater that can cause adverse health effects when released in the environment. As such, there is a growing interest in the development of efficient strategies for the removal of phenolic compounds from polluted water. Herein we describe the use of poly(3,4-ethylenedioxythiophene) (PEDOT)-Au/peroxidase micromotors as dynamic biocatalytic platforms for the removal of model phenolics (phenol, bisphenol A, guaiacol, pyrogallol and catechol). Micromotors are synthetized by using a simplified template electrodeposition protocol followed by covalent enzyme immobilization in the inner Au layer. Kinetic parameters revealed that enzyme immobilization in the inner micromotor layer increased over 2-fold the enzymatic activity, along with increasing operational pH and thermal stabilities. The micromotors can propel at speed of up to 60 µm/s, generating an enhanced fluid mixing that results in removal efficiencies of up to 60% as compared with the 27% removal when using free peroxidase under the same conditions. In addition, excellent activities of almost 100% were obtained within ten cycles of removal using the micromotors. This newly developed bioremediation strategy holds considerable promise in for its application in large scale water treatment systems and many relevant environmental processes.

Cost-Effective, High-Yield Production of Biotemplated Catalytic Tubular Micromotors as Self-Propelled Microcleaners for Water Treatment

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.

Chemically-powered swimming and diffusion in the microscopic world

The past decade has seen intriguing reports and heated debates concerning the chemically-driven enhanced motion of objects ranging from small molecules to millimetre-size synthetic robots. These objects, in solutions in which chemical reactions were occurring, were observed to diffuse (spread non-directionally) or swim (move directionally) at rates exceeding those expected from Brownian motion alone. The debates have focused on whether observed enhancement is an experimental artefact or a real phenomenon. If the latter were true, then we would also need to explain how the chemical energy is converted into mechanical work. In this Perspective, we summarize and discuss recent observations and theories of active diffusion and swimming. Notably, the chemomechanical coupling and magnitude of diffusion enhancement are strongly size-dependent and should vanish as the size of the swimmers approaches the molecular scale. We evaluate the reliability of common techniques to measure diffusion coefficients and finish by considering the potential applications and chemical to mechanical energy conversion efficiencies of typical nanoswimmers and microswimmers.

Recent development of autonomously driven micro/nanobots for efficient treatment of polluted water

Autonomously propelled micro/nanobots are one of the most advanced and integrated structures which have been fascinated researchers owing to its exceptional property that enables them to be carried out user-defined tasks more precisely even on an atomic scale. The unique architecture and engineering aspects of these manmade tiny devices make them viable options for widespread biomedical applications. Moreover, recent development in this line of interest demonstrated that micro/nanobots would be very promising for the water treatment as these can efficiently absorb or degrade the toxic chemicals from the polluted water based on their tunable surface chemistry. These auto propelled micro/nanobots catalytically degrade toxic pollutants into non-hazardous compounds more rapidly and effectively. Thus, for the last few decades, nanobots mediated water treatment gaining huge popularity due to its ease of operation and scope of guided motion that could be monitored by various external fields and stimuli. Also, these are economical, energy-saving, and suitable for large scale water treatment, particularly required for industrial effluents. However, the efficacy of these bots hugely relies on its design, characteristic of materials, properties of the medium, types of fuel, and surface functional groups. Minute variation for one of these things may lead to a change in its performance and hinders its dynamics of propulsion. It is deemed that nanobots might be a smart choice for using these as the new generation devices for treating industrial effluents before discharging it in the water bodies, which is a major concern for human health and the environment.

Fundamentals and applications of enzyme powered micro/nano-motors

Micro/nanomotors (MNMs) are miniaturized machines that can convert many kinds of energy into mechanical motion. Over the past decades, a variety of driving mechanisms have been developed, which have greatly extended the application scenarios of MNMs. Enzymes exist in natural organisms which can convert chemical energy into mechanical force. It is an innovative attempt to utilize enzymes as biocatalyst providing driving force for MNMs. The fuels for enzymatic reactions are biofriendly as compared to traditional counterparts, which makes enzyme-powered micro/nanomotors (EMNMs) of great value in biomedical field for their nature of biocompatibility. Until now, EMNMs with various shapes can be propelled by catalase, urease and many others. Also, they can be endowed with multiple functionalities to accomplish on-demand tasks. Herein, combined with the development process of EMNMs, we are committed to present a comprehensive understanding of EMNMs, including their types, propelling principles, and potential applications. In this review, we will introduce single enzyme that can be used as motor, enzyme powered molecule motors and other micro/nano-architectures. The fundamental mechanism of energy conversion process of EMNMs and crucial factors that affect their movement behavior will be discussed. The current progress of proof-of-concept applications of EMNMs will also be elaborated in detail. At last, we will summarize and prospect the opportunities and challenges that EMNMs will face in their future development.

•

Clear classification and description of different enzyme-powered micro/nanomotors (EMNMs).

•

Discussion of the fundamental mechanism of energy conversion process of EMNMs and their movement influence factors.

•

Introduction of the current progress of proof-of-concept applications of EMNMs.

Chemotaxis-Driven 2D Nanosheet for Directional Drug Delivery toward the Tumor Microenvironment

Micro/nanoscaled motor particles represent a group of intelligent materials that can precisely and rapidly respond to biological microenvironments and improve therapeutic outcomes. In order to maximize biomedical application potentials, developing a nanoscaled motor particle that is able to move autonomously toward a biological target is highly desired but still remains a critical challenge. Herein, a 2D nanosheet-based catalytic nanomotor with chemotaxis behavior is developed for enhanced drug delivery toward the tumor microenvironment. The nanomotors are constructed via a facile one-pot method and exhibit ultrathin monolayer nanosheet morphology. The 2D structure of nanomotors allows high catalytic activity, leading to responsive, sustained, and relatively long distance movement. Importantly, this nanomotor demonstrates directional motion toward the high gradient of H₂ O₂ fuel, exhibiting excellent chemotactic properties. After loading an anticancer drug doxorubicin, the nanomotor shows effective inhibition on cancer cell growth in simulated tumor microenvironments. The practical drug delivery application is further strengthened by the intracellular acidity-triggered biodegradability of the nanomotor after accomplishing the directional drug delivery function. This proof-of-concept work highlights the efficient catalytic activity, tumor microenvironment-guided chemotactic movement, excellent cellular performance of the 2D nanomotor, and opens an avenue for biomedical applications such as controlled and smart drug delivery.

Biofriendly micro/nanomotors operating on biocatalysis: from natural to biological environments

Micro/nanomotors (MNMs) are tiny motorized objects that can autonomously navigate in complex fluidic environments under the influence of an appropriate source of energy. Internal energy-driven MNMs are composed of certain reactive materials that are capable of converting chemical energy from the surroundings into kinetic energy. Recent advances in smart nanomaterials design and processing have endowed the internal energy-driven MNMs with different geometrical designs and various mechanisms of locomotion, with remarkable traveling speed in diverse environments ranging from environmental water to complex body fluids. Among the different design principals, MNM systems that operate from biocatalysis possess biofriendly components, efficient energy conversion, and mild working condition, exhibiting a potential of stepping out of the proof-of-concept phase for addressing many real-life environmental and biotechnological challenges. The biofriendliness of MNMs should not only be considered for in vivo drug delivery but also for environmental remediation and chemical sensing that only environmentally friendly intermediates and degraded products are generated. This review aims to provide an overview of the recent advances in biofriendly MNM design using biocatalysis as the predominant driving force, towards practical applications in biotechnology and environmental technology.

Biocatalytic Micro- and Nanomotors

Enzyme-powered micro- and nanomotors are tiny devices inspired by nature that utilize enzyme-triggered chemical conversion to release energy stored in the chemical bonds of a substrate (fuel) to actuate it into active motion. Compared with conventional chemical micro-/nanomotors, these devices are particularly attractive because they self-propel by utilizing biocompatible fuels, such as glucose, urea, glycerides, and peptides. They have been designed with functional material constituents to efficiently perform tasks related to active targeting, drug delivery and release, biosensing, water remediation, and environmental monitoring. Because only a small number of enzymes have been exploited as bioengines to date, a new generation of multifunctional, enzyme-powered nanorobots will emerge in the near future to selectively search for and utilize water contaminants or disease-related metabolites as fuels. This Minireview highlights recent progress in enzyme-powered micro- and nanomachines.

Rise of cyborg microrobot: different story for different configuration

By integrating organic parts achieved through evolution and inorganic parts developed by human civilisation, the cyborg microrobot is rising by taking advantage of the high flexibility, outstanding energy efficiency, extremely exquisite structure in the natural components and the fine upgradability, nice controllability in the artefact parts. Compared to the purely synthetic microrobots, the cyborg microrobots, due to the exceptional biocompatibility and biodegradability, have already been utilised in in situ diagnosis, precise therapy and other biomedical applications. In this review, through a thorough summary of recent advances of cyborg microrobots, the authors categorise the cyborg microrobots into four major classes according to the configuration between biomaterials and artefact materials, i.e. microrobots integrated inside living cell, microrobots modified with biological debris, microrobots integrated with single cell and microrobots incorporated with multiple cells. Cyborg microrobots with the four types of configurations are introduced and summarised with the combination approaches, actuation mechanisms, applications and challenges one by one. Moreover, they conduct a comparison among the four different cyborg microrobots to guide the actuation force promotion, locomotion control refinement and future applications. Finally, conclusions and future outlook of the development and potential applications of the cyborg microrobots are discussed.

High-performance carbon/MnO2 micromotors and their applications for pollutant removal

The wide applications of particulate micromotors in practice, especially in the removal of environmental pollutants, have been limited by the low production yields and demand on high concentration of fuel such as H₂O₂. Carbon/MnO₂ micromotors were made hydrothermally using different carbon allotropes including graphite, carbon nanotube (CNT), and graphene for treatment of methylene blue and toxic Ag ions. The obtained micromotors showed high speed of self-propulsion. The highest speed of MnO₂-based micromotors to date was observed for CNT/MnO₂ (>2 mm/s, 5 wt% H₂O₂, 0.5 wt% surfactant). Moreover, different from previous studies, even with low H₂O₂ concentration (0.5 wt%) and without surfactant addition, the micromotors could also be well dispersed in water by the O₂ stream released from their reaction with H₂O₂. The carbon/MnO₂ micromotors removed both methylene blue (>80%) and Ag ions (100%) effectively within 15 min by catalytic decomposition and adsorption. Especially high adsorption capacity of Ag (600 mg/g) was measured on graphite/MnO₂ and graphene/MnO₂ micromotors.

A Review of Fast Bubble-Driven Micromotors Powered by Biocompatible Fuel: Low-Concentration Fuel, Bioactive Fluid and Enzyme

Micromotors are extensively applied in various fields, including cell separation, drug delivery and environmental protection. Micromotors with high speed and good biocompatibility are highly desirable. Bubble-driven micromotors, propelled by the recoil effect of bubbles ejection, show good performance of motility. The toxicity of concentrated hydrogen peroxide hampers their practical applications in many fields, especially biomedical ones. In this paper, the latest progress was reviewed in terms of constructing fast, bubble-driven micromotors which use biocompatible fuels, including low-concentration fuels, bioactive fluids, and enzymes. The geometry of spherical and tubular micromotors could be optimized to acquire good motility using a low-concentration fuel. Moreover, magnesium- and aluminum-incorporated micromotors move rapidly in water if the passivation layer is cleared in the reaction process. Metal micromotors demonstrate perfect motility in native acid without any external chemical fuel. Several kinds of enzymes, including catalase, glucose oxidase, and ureases were investigated to serve as an alternative to conventional catalysts. They can propel micromotors in dilute peroxide or in the absence of peroxide.

Powering Motion with Enzymes

Enzymes are ubiquitous in living systems. Apart from traditional motor proteins, the function of enzymes was assumed to be confined to the promotion of biochemical reactions. Recent work shows that free swimming enzymes, when catalyzing reactions, generate enough mechanical force to cause their own movement, typically observed as substrate-concentration-dependent enhanced diffusion. Preliminary indication is that the impulsive force generated per turnover is comparable to the force produced by motor proteins and is within the range to activate biological adhesion molecules responsible for mechanosensation by cells, making force generation by enzymatic catalysis a novel mechanobiology-relevant event. Furthermore, when exposed to a gradient in substrate concentration, enzymes move up the gradient: an example of chemotaxis at the molecular level. The driving force for molecular chemotaxis appears to be the lowering of chemical potential due to thermodynamically favorable enzyme-substrate interactions and we suggest that chemotaxis promotes enzymatic catalysis by directing the motion of the catalyst and substrates toward each other. Enzymes that are part of a reaction cascade have been shown to assemble through sequential chemotaxis; each enzyme follows its own specific substrate gradient, which in turn is produced by the preceding enzymatic reaction. Thus, sequential chemotaxis in catalytic cascades allows time-dependent, self-assembly of specific catalyst particles. This is an example of how information can arise from chemical gradients, and it is tempting to suggest that similar mechanisms underlie the organization of living systems. On a practical level, chemotaxis can be used to separate out active catalysts from their less active or inactive counterparts in the presence of their respective substrates and should, therefore, find wide applicability. When attached to bigger particles, enzyme ensembles act as "engines", imparting motility to the particles and moving them directionally in a substrate gradient. The impulsive force generated by enzyme catalysis can also be transmitted to the surrounding fluid and molecular and colloidal tracers, resulting in convective fluid pumping and enhanced tracer diffusion. Enzyme-powered pumps that transport fluid directionally can be fabricated by anchoring enzymes onto a solid support and supplying the substrate. Thus, enzyme pumps constitute a novel platform that combines sensing and microfluidic pumping into a single self-powered microdevice. Taken in its entirety, force generation by active enzymes has potential applications ranging from nanomachinery, nanoscale assembly, cargo transport, drug delivery, micro- and nanofluidics, and chemical/biochemical sensing. We also hypothesize that, in vivo, enzymes may be responsible for the stochastic motion of the cytoplasm, the organization of metabolons and signaling complexes, and the convective transport of fluid in cells. A detailed understanding of how enzymes convert chemical energy to directional mechanical force can lead us to the basic principles of fabrication, development, and monitoring of biological and biomimetic molecular machines.

Micro- and Nanomotors as Active Environmental Microcleaners and Sensors

The quest to provide clean water to the entire population has led to a tremendous boost in the development of environmental nanotechnology. Toward this end, micro/nanomotors are emerging as attractive tools to improve the removal of various pollutants. The micro/nanomotors either are designed with functional materials in their structure or are modified to target pollutants. The active motion of these motors improves the mixing and mass transfer, greatly enhancing the rate of various remediation processes. Their motion can also be used as an indicator of the presence of a pollutant for sensing purposes. In this Perspective, we discuss different chemical aspects of micromotors mediated environmental cleanup and sensing strategies along with their scalability, reuse, and cost associated challenges.

Self-Propelled Micro/Nanomotors for Sensing and Environmental Remediation

Self-propelled micro/nanomotors have gained attention for successful application in cargo delivery, therapeutic treatments, sensing, and environmental remediation. Unique characteristics such as high speed, motion control, selectivity, and functionability promote the application of micro/nanomotors in analytical sciences. Here, the recent advancements and main challenges regarding the application of self-propelled micro/nanomotors in sensing and environmental remediation are discussed. The current state of micro/nanomotors is reviewed, emphasizing the period of the last five years, then their developments into the future applications for enhanced sensing and efficient purification of water resources are extrapolated.

Progress toward Catalytic Micro- and Nanomotors for Biomedical and Environmental Applications

Synthetic micro- and nanomotors (MNMs) are tiny objects that can autonomously move under the influence of an appropriate source of energy, such as a chemical fuel, magnetic field, ultrasound, or light. Chemically driven MNMs are composed of or contain certain reactive material(s) that convert chemical energy of a fuel into kinetic energy (motion) of the particles. Several different materials have been explored over the last decade for the preparation of a wide variety of MNMs. Here, the discovery of materials and approaches to enhance the efficiency of chemically driven MNMs are reviewed. Several prominent applications of the MNMs, especially in the fields of biomedicine and environmental science, are also discussed, as well as the limitations of existing materials and future research directions.

Boolean-chemotaxis of logibots deciphering the motions of self-propelling microorganisms

We demonstrate the feasibility of a self-propelling mushroom motor, namely a 'logibot', as a functional unit for the construction of a host of optimized binary logic gates. Emulating the chemokinesis of unicellular prokaryotes or eukaryotes, the logibots made stimuli responsive conditional movements at varied speeds towards a pair of acid-alkali triggers. A series of integrative logic operations and cascaded logic circuits, namely, AND, NAND, NOT, OR, NOR, and NIMPLY, have been constructed employing the decisive chemotactic migrations of the logibot in the presence of the pH gradient established by the sole or coupled effects of acid (HCl-catalase) and alkali (NaOH) drips inside a peroxide bath. The imposed acid and/or alkali triggers across the logibots were realized as inputs while the logic gates were functionally reconfigured to several operational modes by varying the pH of the acid-alkali inputs. The self-propelling logibot could rapidly sense the external stimuli, decide, and act on the basis of intensities of the pH triggers. The impulsive responses of the logibots towards and away from the external acid-alkali stimuli were interpreted as the potential outputs of the logic gates. The external stimuli responsive self-propulsion of the logibots following different logic gates and circuits can not only be an eco-friendly alternative to the silicon-based computing operations but also be a promising strategy for the development of intelligent pH-responsive drug delivery devices.

Isolation of HL-60 cancer cells from the human serum sample using MnO2-PEI/Ni/Au/aptamer as a novel nanomotor and electrochemical determination of thereof by aptamer/gold nanoparticles-poly(3,4-ethylene dioxythiophene) modified GC electrode

Herein, aptamer-modified self-propelled nanomotors were used for transportation of human promyelocytic leukemia cells (HL-60) from a human serum sample. For this purpose, the fabricated manganese oxide nanosheets-polyethyleneimine decorated with nickel/gold nanoparticles (MnO₂-PEI/Ni/Au) as nanomotors were added to a vial containing thiolated aptamer KH1C12 solution as a capture aptamer to attach to the gold nanoparticles on the surface of nanomotors covalently. The aptamer-modified self-propelled nanomotors (aptamer_KH1C12/nanomotors) were then separated by placing the vial in a magnetic stand. The aptamer-modified self-propelled nanomotors were rinsed three times with water to remove the non-attached aptamers. Then, the resulting aptamer_KH1C12/nanomotors were applied for the on-the-fly" transporting of HL-60 cancer cell from a human serum sample. To release of the captured HL-60 cancer cells, the complementary nucleotide sequences of KH1C12 aptamer solution (releasing aptamer) that has a with capture aptamer was added to phosphate buffer solution (1 M, pH 7.4) containing HL-60/aptamer_KH1C12/nanomotors. Because of the high affinity of capture aptamer to complementary nucleotide sequences of aptamer_KH1C12, the HL-60 cancer cells released on the surface of aptamer_KH1C12/nanomotors into the solution. The second goal of the present work was determining the concentration of HL-60 cancer cell in the human serum samples. The electrochemical impedance spectroscopy technique (EIS) was used for the determination of HL-60 cancer cell. The concentration of separated cancer cell was determined by aptamer/gold nanoparticles-poly(3,4-ethylene dioxythiophene) modified GC electrode (GC/PEDOT-Au_nano/aptamer _KH1C12). The proposed aptasensor exhibited a good response to the concentration of HL-60 cancer cells in the range of 2.5 × 10¹ to 5 × 10⁵ cells mL^-1 with a low limit of detection of 250 cells mL^-1.

Nano- and micromotors for cleaning polluted waters: focused review on pollutant removal mechanisms

Nano- and micromotors are machines designed to self-propel and-in the process of propelling themselves-perform specialized tasks like cleaning polluted waters. These motors offer distinct advantages over conventionally static decontamination methods, owing to their ability to move around and self-mix-which heightens the interaction between their active sites and target pollutants-thus improving their speed and efficiency, which could potentially decrease treatment times and costs. In the last decade, considerable research efforts have been expended on exploring various mechanisms by which these motors can self-propel and remove pollutants, proving that the removal of oil droplets, heavy metals, and organic compounds using these synthetic motors is possible. This review highlights recent progress in the design of these nano- and micromotors for cleaning polluted waters, and gives an overview of their structure, fabrication, and propulsion methods, with a special focus on the mechanisms by which they remove pollutants-namely, either by adsorption or by degradation. A fundamental understanding of these removal mechanisms, with their attendant advantages and disadvantages, can help researchers fine-tune motor design in the future so that technical issues can be resolved before they are scaled-up for a wide variety of environmental applications.

Enzyme Catalysis To Power Micro/Nanomachines

Enzymes play a crucial role in many biological processes which require harnessing and converting free chemical energy into kinetic forces in order to accomplish tasks. Enzymes are considered to be molecular machines, not only because of their capability of energy conversion in biological systems but also because enzymatic catalysis can result in enhanced diffusion of enzymes at a molecular level. Enlightened by nature's design of biological machinery, researchers have investigated various types of synthetic micro/nanomachines by using enzymatic reactions to achieve self-propulsion of micro/nanoarchitectures. Yet, the mechanism of motion is still under debate in current literature. Versatile proof-of-concept applications of these enzyme-powered micro/nanodevices have been recently demonstrated. In this review, we focus on discussing enzymes not only as stochastic swimmers but also as nanoengines to power self-propelled synthetic motors. We present an overview on different enzyme-powered micro/nanomachines, the current debate on their motion mechanism, methods to provide motion and speed control, and an outlook of the future potentials of this multidisciplinary field.

Dynamic Loading and Unloading of Proteins in Polymeric Stomatocytes: Formation of an Enzyme-Loaded Supramolecular Nanomotor

Self-powered artificial nanomotors are currently attracting increased interest as mimics of biological motors but also as potential components of nanomachinery, robotics, and sensing devices. We have recently described the controlled shape transformation of polymersomes into bowl-shaped stomatocytes and the assembly of platinum-driven nanomotors. However, the platinum encapsulation inside the structures was low; only 50% of the structures contained the catalyst and required both high fuel concentrations for the propelling of the nanomotors and harsh conditions for the shape transformation. Application of the nanomotors in a biological setting requires the nanomotors to be efficiently propelled by a naturally available energy source and at biological relevant concentrations. Here we report a strategy for enzyme entrapment and nanomotor assembly via controlled and reversible folding of polymersomes into stomatocytes under mild conditions, allowing the encapsulation of the proteins inside the stomach with almost 100% efficiency and retention of activity. The resulting enzyme-driven nanomotors are capable of propelling these structures at low fuel concentrations (hydrogen peroxide or glucose) via a one-enzyme or two-enzyme system. The confinement of the enzymes inside the stomach does not hinder their activity and in fact facilitates the transfer of the substrates, while protecting them from the deactivating influences of the media. This is particularly important for future applications of nanomotors in biological settings especially for systems where fast autonomous movement occurs at physiological concentrations of fuel.