Comprehensive Understanding of Self-Propelled Janus Pt/Fe2O3 Micromotor Dynamics: Impact of Size, Morphology, and Surface Structure

The increasing use of plastics has led to the accumulation of plastic waste in the oceans, resulting in significant global environmental challenges associated with microplastic pollution. Micromotors, capable of capturing and removing microplastics from aquatic systems, have emerged as a promising solution to addressing this problem. This research aims to analyze the factors affecting the speed of micromotors, including size, morphology, and surface structure, while elucidating the underlying mechanisms governing micromotor propulsion to develop efficient and ecofriendly micromotors. In this study, we systematically manipulate various parameters by modifying the synthesis method of hematite-based micromotors, subsequently comparing their propulsion speeds and uncovering the precise role of these parameters in determining the micromotor performance. Furthermore, we shed light on the intricate interplay between drag force and propulsive force, demonstrating how these forces vary under different H2O2 conditions. These findings provide valuable insights into the design of efficient micromotors tailored for dynamic aquatic environments.

Smart micro- and nanorobots for water purification

Less than 1% of Earth's freshwater reserves is accessible. Industrialization, population growth and climate change are further exacerbating clean water shortage. Current water-remediation treatments fail to remove most pollutants completely or release toxic by-products into the environment. The use of self-propelled programmable micro- and nanoscale synthetic robots is a promising alternative way to improve water monitoring and remediation by overcoming diffusion-limited reactions and promoting interactions with target pollutants, including nano- and microplastics, persistent organic pollutants, heavy metals, oils and pathogenic microorganisms. This Review introduces the evolution of passive micro- and nanomaterials through active micro- and nanomotors and into advanced intelligent micro- and nanorobots in terms of motion ability, multifunctionality, adaptive response, swarming and mutual communication. After describing removal and degradation strategies, we present the most relevant improvements in water treatment, highlighting the design aspects necessary to improve remediation efficiency for specific contaminants. Finally, open challenges and future directions are discussed for the real-world application of smart micro- and nanorobots.

Micro‐ and Nanorobots Meet DNA

DNA, the well‐known molecule that carries the genetic information of almost all forms of life, represents a pivotal element in formulating intelligent and versatile micro/nanorobotic systems. DNA‐functionalized micro/nanorobots have opened new and exciting opportunities in many research areas due to the synergistic combination of self‐propulsion at the micro/nanoscale and the high specificity and programmability of DNA interactions. Here, their designs and applications are critically reviewed, which span from the use of DNA as the fuel to chemotactically power nanorobots toward cancer cells to DNA as the main building block for sophisticated phototactic biorobots, DNA nanodevices to self‐monitor microrobots’ activity status, DNA and RNA sensing, nucleic acids isolation, gene therapy, and water purification. The perspective on future directions of the field is also shared, envisioning DNA‐mediated reconfigurable assemblies of nanorobotic swarms.

Shape-Controlled Self-Assembly of Light-Powered Microrobots into Ordered Microchains for Cells Transport and Water Remediation

Nature presents the collective behavior of living organisms aiming to accomplish complex tasks, inspiring the development of cooperative micro/nanorobots. Herein, the spontaneous assembly of hematite-based microrobots with different shapes is presented. Autonomous motile light-driven hematite/Pt microrobots with cubic and walnut-like shapes are prepared by hydrothermal synthesis, followed by the deposition of a Pt layer to design Janus structures. Both microrobots show a fuel-free motion ability under light irradiation. Because of the asymmetric orientation of the magnetic dipole moment in the crystal, cubic hematite/Pt microrobots can self-assemble into ordered microchains, contrary to the random aggregation observed for walnut-like microrobots. The microchains exhibit different synchronized motions under light irradiation depending on the mutual orientation of the individual microrobots during the assembly, which allows them to accomplish multiple tasks, including capturing, picking up, and transporting microscale objects, such as yeast cells and suspended matter in water extracted from personal care products, as well as degrading polymeric materials. Such light-powered self-assembled microchains demonstrate an innovative cooperative behavior for small-scale multitasking artificial robotic systems, holding great potential toward cargo capture, transport, and delivery, and wastewater remediation.

Prussian Blue/Chitosan Micromotors with Intrinsic Enzyme-like Activity for (bio)-Sensing Assays

Prussian Blue (PB)/chitosan enzyme mimetic tubular micromotors are used here for on-the-fly (bio)-sensing assays. The micromotors are easily prepared by direct deposition of chitosan into the pores of a membrane template and in situ PB synthesis during hydrogel deposition. Under judicious pH control, PB micromotors display enzyme mimetic capabilities with three key functions on board: the autonomous oxygen bubble propulsion (with PB acting as a catalase mimic for hydrogen peroxide decomposition), 3,3',5,5'-tetramethylbenzidine (TMB) oxidation (with PB acting as a peroxidase mimic for analyte detection), and as a magnetic material (to simplify the (bio)-sensing steps). In connection with chitosan capabilities, these unique enzyme mimetic micromotors are further functionalized with acetylthiocholinesterase enzyme (ATChE) to be explored in fast inhibition assays (20 min) for the colorimetric determination of the nerve agent neostigmine, with excellent analytical performance in terms of quantification limit (0.30 μM) and concentration linear range (up to 500 μM), without compromising efficient micromotor propulsion. The new concept illustrated holds considerable potential for a myriad of (bio)-sensing applications, including forensics, where this conceptual approach remains to be explored. Micromotor-based tests to be used in crime scenes are also envisioned due to the reliable neostigmine determination in unpretreated samples.

Photo-Fenton Degradation of Nitroaromatic Explosives by Light-Powered Hematite Microrobots: When Higher Speed Is Not What We Go For

Self-powered micromachines are considered a ground-breaking technology for environmental remediation. Light-powered Janus microrobots based on photocatalytic semiconductors asymmetrically covered with metals have recently received great interest as they can exploit light to move and contemporarily degrade pollutants in water. Although various metals have been explored and compared to design Janus microrobots, the influence of the metal layer thickness on motion behavior and photocatalytic properties of microrobots have not been investigated yet. Here, light-driven hematite/Pt Janus microrobots are reported and fabricated by depositing Pt layers with different thickness on hematite microspheres produced by hydrothermal synthesis. It has been demonstrated that the thicker the metal layer the higher the microrobots speed. However, when employed for the degradation of nitroaromatic explosives pollutants through the photo-Fenton mechanism, higher rate of H₂ O₂ consumption leads to higher propulsion speed of microrobots and lower pollutants degradation efficiencies owing to less H₂ O₂ involved in the photo-Fenton reaction. This work presents new insights into the motion behavior of light-powered Janus micromotors and demonstrates that high speed is not what really matters for water purification via photo-Fenton reaction, which is important for the future environmental applications of micromachines.

Polypyrrole-Based Nanorobots Powered by Light and Glucose for Pollutant Degradation in Water

Novel photoactive and enzymatically active nanomotors were developed for efficient organic pollutant degradation. The developed preparation route is simple and scalable. Light-absorbing polypyrrole nanoparticles were equipped with a bi-enzyme [glucose oxidase/catalase (GOx/Cat)] system enabling the simultaneous utilization of light and glucose as energy sources for jet-induced nanoparticle movement and active radical production. The GOx utilizes glucose to produce hydrogen peroxide, which is subsequently degraded by Cat, resulting in the generation of active radicals and/or oxygen bubbles that propel the particles. Uneven grafting of GOx/Cat molecules on the nanoparticle surface ensures inhomogeneity of peroxide creation/degradation, providing the nanomotor random propelling. The nanomotors were tested for their ability to degrade chlorophenol, under various experimental conditions, that is, with and without simulated sunlight illumination or glucose addition. In all cases, degradation was accelerated by the presence of the self-propelled nanoparticles or light illumination. Light-induced heating also positively affects enzymatic activity, further accelerating nanomotor diffusion and pollutant degradation. In fact, the chemical and photoactivities of the nanoparticles led to more than 95% removal of chlorophenol in 1 h, without any external stirring. Finally, the quality of the purified water and the extent of pollutant removal were checked using an eco-toxicological assay, with demonstrated significant synergy between glucose pumping and sunlight illumination.

Fabrication, application, optimization and working mechanism of Fe2O3 and its composites for contaminants elimination from wastewater

Fe₂O₃ and its composites have been extensively investigated and employed for the remediation of contaminated water with the characteristics of low cost, outstanding chemical stability, high efficiency of visible light utilization, excellent magnetic ability and abundant active sites for adsorption and degradation. In this review, the potentials of Fe₂O₃ in water remediation were discussed and summarized in detail. Firstly, various synthesis methods of Fe₂O₃ and its composites were reviewed and compared. Based on the structures and characteristics of the obtained materials, their applications and related mechanisms in pollutants removal were surveyed and discussed. Furthermore, several strategies for optimizing the remediation processes, including dispersion, immobilization, nano/micromotor construction and simultaneous decontamination, were also highlighted and discussed. Finally, recommendations for further work in the development of novel Fe₂O₃-related materials and its practical applications were proposed.

Biomedical applications of metal–organic framework (MOF)-based nano-enzymes

In the present review, the types and activities of nanometer-sized enzymes are summarized, with recent progress of nanometer-sized enzymes in the field of biomedical detection.

Carbonate Micromotors for Treatment of Construction Effluents

Concrete in construction has recently gained media coverage for its negative CO₂ footprint, but this is not the only problem associated with its use. Due to its chemical composition, freshly poured concrete changes the pH of water coming in contact with the surface to very alkaline values, requiring neutralization treatment before disposal. Conventional methods include the use of mineral acid or CO₂ pumps, causing high costs to building companies. In this paper, we present a micromotor based remediation strategy, which consists of carbonate particles half-coated with citric acid. To achieve this half coverage spray coating is used for the first time to design Janus structures. The motors propel diffusiophoretically due to a self-generated gradient formed as the acid coverage dissolves. The locally lower pH contributes to the dissolution of the carbonate body. These motors have been employed to study neutralization of diluted concrete wash water (CWW) at microscopic scale and we achieve visualization of the pH changes occurring in the vicinity of motors using anthocyanine as pH indicator dye. The effect of citric acid-carbonates hybrid on neutralization of real CWW on macroscopic scale has also been studied. In addition, all employed chemicals are cheap, non-toxic and do not leave any solid residues behind.