Self-propelled Micromachines Research Articles

Photocatalytic Pt/Ag3VO4 micromotors with inherent sensing capabilities for corroding environments

Autonomous self-propelled micromachines based on semiconductors are at the forefront of environmental pollutants degradation research to palliate the effects of the contamination arising from the constant manufacturing of new products. Nonetheless, testing these micromotors with real-life products is almost an unexplored field, limiting the degradation of pollutants to single-component aqueous solutions or suspensions at the laboratory scale, which hinders the translation of these micromachines into useful systems. Herein, Ag3VO4 has been devised as a micromotor by an asymmetric deposition of a thin layer of Pt, giving rise to Pt/Ag3VO4 micromotors (Janus particle). Their motion capabilities have been demonstrated under UV light in fuel-free conditions. Their photocatalytic performance at laboratory scale has been confirmed for the degradation of Rhodamine B while, as a first approximation of a real-life application, the degradation of an energy drink has also been tested. During this latter exploration, the Pt/Ag3VO4 micromotors were corroded by the citric acid present in the pollutant, releasing Ag nanoparticles into the media. As a proof of concept, the position of the generated Ag nanoparticles’ surface plasmon resonance absorption maximum has been demonstrated to show a dependency on the concentration of citric acid.

Chemical Microrobots as Self-Propelled Microbrushes against Dental Biofilm

Mouths offer the perfect environments for microbial cell formation, promoting the growth of biofilms, for example, on teeth. Dental biofilm exhibits strong resistance to antibiotics and is a cause of many dental diseases. Common strategies for dental biofilm removal involve the addition of high concentrations of hydrogen peroxide (H 2 O 2 ), which increases tooth sensitivity, or mechanical procedures. Here, we report a different approach based on self-propelled micromachines with high antibacterial activity for the degradation of dental biofilm. Such microrobots use low concentrations of fuel for their propulsion, and they achieve an efficient dental biofilm disruption in only 5 min of treatment. Moreover, these microrobots are biocompatible with epidermal and organ cells and may stimulate the immune system to fight against microbial infection. This approach of exploiting the active motion of bubble-propelled catalytic micromachines for oral biofilm disruption may open the door for more efficient and sophisticated treatments in dentistry. The ability of catalytic microrobots to disrupt dental biofilm is demonstrated 95% killing efficiency is obtained after 5 min of treatment The biocompatibility of these microrobots with epidermal and organ cells is confirmed Autonomous self-propelled tubular microrobots based on titanium dioxide decorated with platinum nanoparticles were developed by Villa et al. for the degradation of dental biofilm strains. The killing ability of these micromachines is attributed to their antibacterial activity and the continuous generation of microbubbles at the biofilm surface.

Radioactive Uranium Preconcentration via Self-Propelled Autonomous Microrobots Based on Metal-Organic Frameworks.

Self-propelled micromachines have recently attracted attention for environmental remediation, yet their use for radioactive waste management has not been addressed. Engineered micromotors that are able to combine highly adsorptive capabilities together with fast autonomous motion in liquid media are promising tools for the removal of nuclear waste, which is one of the most difficult types to manage. Herein, we fabricate self-propelled micromotors based on metal-organic frameworks (MOFs) via template-based interfacial synthesis and show their potential for efficient removal of radioactive uranium. A crucial challenge of the MOF-based motors is their stability in the presence of fuel (hydrogen peroxide) and acidic media. We have ensured their structural stability by Fe doping of zeolitic imidazolate framework-8 (ZIF-8). The implementation of magnetic ferroferric oxide nanoparticles (Fe3O4 NPs) and catalytic platinum nanoparticles (Pt NPs) results in the magnetically responsive and bubble-propelled micromotors. In the presence of 5 wt % H2O2, these micromotors are propelled at a high speed of ca. 860 ± 230 μm·s-1 (i.e., >60 body lengths per second), which is significantly faster than that of other microrod-based motors in the literature. These micromotors demonstrate a highly efficient removal of uranium (96%) from aqueous solution within 1 h, with the subsequent recovery under magnetic control, as well as stable recycling ability and high selectivity. Such self-propelled magnetically recoverable micromotors could find a role in the management and remediation of radioactive waste.

Light-Driven ZnO Brush-Shaped Self-Propelled Micromachines for Nitroaromatic Explosives Decomposition.

Self-propelled micromachines have recently attracted lots of attention for environmental remediation. Developing a large-scale but template-free fabrication of self-propelled rod/tubular micro/nanomotors is very crucial but still challenging. Here, a new strategy based on vertically aligned ZnO arrays is employed for the large-scale and template-free fabrication of self-propelled ZnO-based micromotors with H2 O2 -free light-driven propulsion ability. Brush-shaped ZnO-based micromotors with different diameters and lengths are fully studied, which present a fast response to multicycles UV light on/off switches with different interval times (2/5 s) in pure water and slow directional motion in aqueous hydrogen peroxide solution in the absence of UV light. Light-induced electrophoretic and self-diffusiophoretic effects are responsible for these two different self-motion behaviors under different conditions, respectively. In addition, the pH of the media and the presence of H2 O2 show important effects on the motion behavior and microstructure of the ZnO-based micromotors. Finally, these novel ZnO-based brush-shaped micromotors are demonstrated in a proof-of-concept study on nitroaromatic explosive degradation, i.e., picric acid. This work opens a completely new avenue for the template-free fabrication of brush-shaped light-responsive micromotors on a large scale based on vertically aligned ZnO arrays.

Self-propelled micromachines for analytical sensing: a critical review.

Self-propelled micromotors are micro- and nanoscale devices that move autonomously in solution by converting a specific stimulus into mechanical work. The broad scope of operations and applications along with the ultra-small dimensions have opened new possibilities to solve complex analytical challenges. Herein we give a critical overview of early developments and future prospects of such tiny moving objects for different analytical sensing and biosensing strategies. From early electrophoretic propelled nanomotors, which were limited to low viscous media, to bubble-propelled micromotors, the field has evolved into sophisticated all-in-one analytical systems with built-in sensing capabilities. Current progress for in vivo biosensing and integration into analytical instrumentation towards fully functional devices will be also covered. We hope that this review provides the reader with some general knowledge and future prospects of self-propelled micromachines as a new paradigm in analytical chemistry. Graphical abstract.

Functional 2D Germanene Fluorescent Coating of Microrobots for Micromachines Multiplexing.

Micromachines are at the forefront of materials research as they are self-propelled, smart autonomous systems capable of acting as an intelligent matter. One of the obstacles the field faces is tracking individual micromachines carrying molecular cargo from the rest of the micromachines. Highly stable fluorescent markers based on chemically modified 2D germanene compounds are developed. Two different 2D germanene derivatives, 4-fluorophenylgermanane (2D-Ph-Ge) and methylgermanane (2D-Me-Ge), exhibit different fluorescence under UV light irradiation (excitation at 365 nm), which allows one particular micromotor to be easily distinguished in a mixture of micromotors. This offers a paradigm shift toward a new approach of multiplex detection of self-propelled micromachines. The utility is demonstrated on a drug delivery system, where micromachines carrying a drug are labeled with 2D-Ph-Ge with blue emission while bare micromachines are labeled by 2D-Me-Ge with red emission. This approach of functional fluorescent labeling will pave the way to multiple simultaneous functionalized micromachines identification in complex environments.

Micromotor-Assisted Human Serum Glucose Biosensing.

Artificial self-propelled micromachines have shown great promise in biomedical sciences. In this work, we use Mg/Pt Janus micromotors with self-rejuvenating surfaces to enhance the electrochemical sensing performance and sensitivity toward glucose in human serum. The detection of glucose is based on the glucose oxidase enzyme and ferrocenemethanol shuttle system, where mass transfer was dramatically enhanced by the rapid motion of Mg/Pt Janus micromotors. The obtained chronoamperometric data show that Mg/Pt Janus micromotors play a synergistic role in enhancing the current response at millimolar concentrations of glucose in human serum. The current signals increased with the corresponding increase in amount of micromotors introduced. Furthermore, a linear relationship between current signal and glucose concentration was established, while the limit of detection improved when mobile Mg/Pt Janus micromachines were used. Glucose detection enhanced by micromachines may pave the way for their future applications in biomedicine and medical diagnostic devices.

Structure–Function Dependence on Template-Based Micromotors

Catalytically bubble propelled micromotors are one of the most frequently used self-propelled micromachines in the literature. Typically, the structure–function relationship is not investigated. We present detailed study of how the structural geometry influences the propulsion of these micromachines. We prepared different micromotors with membrane template-assisted electrodeposition by applying varied electroplating time. We obtained a variety of differently sized micromotors with a range of propulsion dynamics. We used varied electroplating time to tailor the length of the micromotor, but also the wall thickness, microtube opening diameter, and even the structural integrity of the micromotor. The study of propulsion dynamics of micromotors in different H2O2 concentrations indicated that both geometric parameters and the chemical environment affect the velocity of micromotors. Microtubular motors prepared by short electrodeposition time (e.g., 300 s) require higher fuel concentration to activate and move....

Controllable Swarming and Assembly of Micro/Nanomachines.

Motion is a common phenomenon in biological processes. Major advances have been made in designing various self-propelled micromachines that harvest different types of energies into mechanical movement to achieve biomedicine and biological applications. Inspired by fascinating self-organization motion of natural creatures, the swarming or assembly of synthetic micro/nanomachines (often referred to micro/nanoswimmers, micro/nanorobots, micro/nanomachines, or micro/nanomotors), are able to mimic these amazing natural systems to help humanity accomplishing complex biological tasks. This review described the fuel induced methods (enzyme, hydrogen peroxide, hydrazine, et al.) and fuel-free induced approaches (electric, ultrasound, light, and magnetic) that led to control the assembly and swarming of synthetic micro/nanomachines. Such behavior is of fundamental importance in improving our understanding of self-assembly processes that are occurring on molecular to macroscopic length scales.

Self-Propelled Metal-Polymer Hybrid Micromachines with Bending and Rotational Motions.

Two self-propelled micromachines were fabricated with gold/platinum micromotors that exhibit simple translational motion in a fuel solution. In each one, two micromotors were connected with a joint of polymer tube formed by stacking cationic poly(allylamine hydrochloride) (PAH) and anionic poly(acrylic acid) (PAA) using a layer-by-layer technique. A bent structure was created by making one longitudinal side of the joint more swellable with alkaline treatment. The joint containing fewer PAA/PAH bilayers was flexible and allowed a larger range of Brownian angular fluctuation. In the fuel solution, bending and stable rotation were observed for the micromotors tethered with soft and rigid angled joints, respectively. The radius and angular velocity of the rotation depended on the angle of the joint. Such tethered micromotors can be used to realize sophisticated micro/nanomachines for microscale surgery and drug delivery.

Catalytic DNA-Functionalized Self-Propelled Micromachines for Environmental Remediation

Summary Toward addressing mercury contamination, DNA-functionalized microtubes that can serve as the next generation of self-propelled catalytic micromachines to remove Hg(II) from aqueous solution are described. The microtubes, prepared via the electrodeposition method, are composed of an inner platinum catalytic surface for self-propulsion and a gold outer surface for functionalization with DNA. The highly specific and strong binding of Hg(II) to T-T mismatched pairs in DNA sequences confers the adsorption capability for Hg(II) on the microtubes. The efficient self-propulsion of these micromachines results in enhanced removal of Hg(II). The autonomous micromotor-based strategy provides a dynamic adsorption platform for decontamination of mercury-polluted water bodies.