Catalytic Micromotors Research Articles

Dual on-the-move electrochemical immunoassays for the simultaneous determination of amyloid-β (1−42) and Tau in Alzheimer's patient samples

Here, we report catalytic micromotors (MM)-based electrochemical immunoassays for the on-the-move dual and simultaneous determination of Amyloid-β (Aβ-42) and Tau protein (Tau) (MMAβ-42-MMTau) as relevant Alzheimer’s disease biomarkers in brain tissue, cerebrospinal fluid, and plasma diagnosed samples. Combining the binding capacity of the antibody's functionalized polypyrrole (PPy) layer of MM with the self-propulsion from the PtNPs layer thanks to the decomposition of hydrogen peroxide, the approach yielded excellent detection limits (LODAβ-42=0.04 ng/mL, LODTau= 0.4 pg/mL) using low sample volumes (30 µL) and short analysis times (15 min) to detect both biomarkers. Quantitative analysis by MMAβ-42-MMTau was carried out without any clinical sample dilution (linear ranges are between 0.1 and 5 ng/mL for Aβ-42 and from 1 to 106 pg/mL in the case of Tau), highlighting the versatility of the approach to quantify Aβ-42 and Tau levels at different dynamic ranges. MMAβ-42-MMTau showed superior analytical capabilities to the single molecule counting technology (SMCx) during quantitative analysis in all sample classes tested, reporting a difference in quantitative levels for both biomarkers between healthy and diseased individuals and an increase in the levels with disease progression, except in plasma samples where no relationship between biomarker levels and disease progression was found.

The role of self-diffusiophoresis and reactive force during the propulsion of manganese-based catalytic micromotors.

The movement of catalytic micromotors is often accompanied by gas generation. Currently, the prevailing view is that bubbles play a significant role in their movement. Analyzing the movements of catalytic manganese-based micromotors in a solution of hydrogen peroxide, we found that the reactive force cannot play a significant role in their movement, and the main mechanism occurs due to self-diffusiophoresis.

Magnetic Manganese‐Based Micromotors MnFe2O4@Fe3O4/graphite and Mn2O3@Fe2O3@Fe3O4/graphite for Organic Pollutant Degradation

AbstractWastewater pollution with organic compounds poses a serious threat to human health. One of the possible methods for solving these problems can be the use of micro/nanomotors. Among them, manganese‐based micro/nanomotors have a number of important advantages related to high catalytic activity, powerful motion, and low cost. Due to their mobility, micro/nanomotors promote an increase in the intensity of mass transfer in the reacting system. When introducing ferromagnetic elements into manganese‐based micro/nanomotors, it is possible not only to increase their motion speed, but also to make their motion more controllable. Herein, for the first time it demonstrates a synthesis method for MnFe2O4@Fe3O4/graphite and Mn2O3@Fe2O3@Fe3O4/graphite magnetic catalytic micromotors, which have remarkable photocatalytic properties. Micromotors are clusters of nanoparticles whose motion in a hydrogen peroxide solution in a non‐uniform magnetic field is caused by the action of magnetic force and self‐diffusiophoresis. Nanoparticles are synthesized by the plasma‐arc method with subsequent annealing in the air. When changing the annealing temperature, the catalytic and magnetic properties of nanoparticles can vary within a wide range of values. Micromotors MnFe2O4@Fe3O4/graphite have the most optimal catalytic and magnetic properties. The results of the research show that these micromotors are effective catalysts in the decomposition of methylene blue.

Versatile synthesis of hollow PDA motors by interfacial protection

Micro/nanomotors (MNMs) are miniaturized devices capable of autonomous motion and on-demand task execution, which have broad application prospects in environmental remediation and biomedicine. However, miniaturization makes it difficult for chemically driven MNMs to integrate functional parts to perform tasks in a simple way. Here, we present a novel approach to manufacture asymmetric, hollow, modifiable and catalytic micromotors by the interfacial protection of polystyrene (PS) and inherent property of polydopamine (PDA). The hollow PDA microparticle with a single hole on its surface, as the main structure of the micromotors, is fabricated by swelling-induced symmetry breaking. Due to interfacial protection of PS, the functional component platinum nanoparticle (PtNP) can be selectively assembled on the outer or inner of the hollow PDA particle, respectively. Benefiting from the geometric shape and composition characteristics, PtNP-modified PDA motors can perform self-propulsion and catalyze the decomposition of methylene blue (MB) during motion. Moreover, the successful loading of nanoparticles with different functions (AuNP, Fe3O4 and MnO2) enables it to fabricate different functional MNMs as required. In short, the strategy is a versatile, general for designing asymmetric hollow MNMs with adjustable function by virtue of interfacial protection and functionalized PDA.

Automated control of catalytic Janus micromotors

Automated control of catalytic Janus micromotors

Programming Motion of Platinum Microparticles: From Linear to Orbital

Self-powered catalytic micromotors that swim through a fluid by harvesting energy from their environment have received increasing attention because of their potential applications in nanomachinery, nanoscale assembly, and robotics. However, persistent directional motion is required for micromotors to perform useful work. Herein, through modeling and experiments, we demonstrate the general design strategy for single-component platinum micromotors that, in the presence of hydrogen peroxide, can execute a variety of motion trajectories from extremely linear to orbital. This is achieved via a simple shape design wherein the speed and directionality of a particle are determined by overall symmetry elements. Shape design gives high reproducibility and allows a wide range of adjustments to fine-tune the desired particle motion. We observe strong agreement between experimental data and numerical predictions, indicating that our model can serve to predict directionality and speed of a particle prior to fabrication. Shape programming works on an individual-particle basis, thus enabling complex systems which require different modes of motion for the individual parts.

Catalytic micromotors as self-stirring microreactors for efficient dual-mode colorimetric detection

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

Addition to On the Move-Sensitive Fluorescent Aptassay on Board Catalytic Micromotors for the Determination of Interleukin-6 in Ultra-Low Serum Volumes for Neonatal Sepsis Diagnostics

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionAddition to On the Move-Sensitive Fluorescent Aptassay on Board Catalytic Micromotors for the Determination of Interleukin-6 in Ultra-Low Serum Volumes for Neonatal Sepsis DiagnosticsJosé GordónJosé GordónMore by José Gordón, Luis ArruzaLuis ArruzaMore by Luis Arruza, María Dolores IbáñezMaría Dolores IbáñezMore by María Dolores Ibáñez, María Moreno-GuzmánMaría Moreno-GuzmánMore by María Moreno-Guzmánhttps://orcid.org/0000-0003-3761-0542, Miguel Ángel LópezMiguel Ángel LópezMore by Miguel Ángel López, and Alberto EscarpaAlberto EscarpaMore by Alberto Escarpahttps://orcid.org/0000-0002-7302-0948Cite this: ACS Sens. 2023, 8, 1, 403Publication Date (Web):January 9, 2023Publication History Received13 December 2022Published online9 January 2023Published inissue 27 January 2023https://doi.org/10.1021/acssensors.2c02731Copyright © 2023 The Authors. Published by American Chemical SocietyRIGHTS & PERMISSIONSACS AuthorChoiceCC: Creative CommonsBY: Credit must be given to the creatorArticle Views183Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1003 KB) Get e-Alerts Get e-Alerts

Analyte Sensing with Catalytic Micromotors

Catalytic micromotors can be used to detect molecules of interest in several ways. The straightforward approach is to use such motors as sensors of their "fuel" (i.e., of the species consumed for self-propulsion). Another way is in the detection of species which are not fuel but still modulate the catalytic processes facilitating self-propulsion. Both of these require analysis of the motion of the micromotors because the speed (or the diffusion coefficient) of the micromotors is the analytical signal. Alternatively, catalytic micromotors can be used as the means to enhance mass transport, and thus increase the probability of specific recognition events in the sample. This latter approach is based on "classic" (e.g., electrochemical) analytical signals and does not require an analysis of the motion of the micromotors. Together with a discussion of the current limitations faced by sensing concepts based on the speed (or diffusion coefficient) of catalytic micromotors, we review the findings of the studies devoted to the analytical performances of catalytic micromotor sensors. We conclude that the qualitative (rather than quantitative) analysis of small samples, in resource poor environments, is the most promising niche for the catalytic micromotors in analytical chemistry.

Optical motion control of catalytic WS2 and MoS2 micromotors

Herein we described the on-demand optically controlled braking and acceleration of transition metal dichalcogenide (TMD) based tubular catalytic micromotors. The direct electrodeposition of a thin WS2 or MoS2 outer layer imparts the micromotors with a direct bandgap for built-in optical responsive properties, along with light-induced heating. Thus, up to 70% speed acceleration is observed after irradiation from 365 to 535 nm. The phenomena can be explained by a mixed effect of electron generation and promotion from the active electronic levels of the outer WS2 or MoS2 micromotor layer, which recombines with the Pt layer, generating an additional peroxide input for increased speeds. The inherent photothermal properties of the TMD outer layer of the micromotors after light interaction also result in an increase in the temperature of the inner catalytic Pt layer, which results in increased decomposition kinetics. On-demand braking and acceleration of the micromotors can be thus achieved in the full electromagnetic spectrum, representing an alternative approach to control catalytic micromotor propulsion for a myriad of applications.

Droplet microfluidic synthesis of shape-tunable self-propelled catalytic micromotors and their application to water treatment

Droplet microfluidic synthesis of shape-tunable self-propelled catalytic micromotors and their application to water treatment

On the Move-Sensitive Fluorescent Aptassay on Board Catalytic Micromotors for the Determination of Interleukin-6 in Ultra-Low Serum Volumes for Neonatal Sepsis Diagnostics.

A graphene oxide/nickel/platinum nanoparticle micromotor (MM)-based fluorescent aptassay is proposed to determine interleukin-6 (IL-6) in serum samples from low-birth-weight infants (gestational age of less than 32 weeks and birthweight below 1000 g) with sepsis suspicion. In this kind of patients, IL-6 has demonstrated good sensitivity and specificity for the diagnosis of sepsis, both for early and late onset sepsis. The approach was based on the adsorption of the aptamer for IL-6 tagged with 6-FAM as a fluorescent label (AptIL-6, λem = 520 nm) on the graphene oxide external layer (MMGO-AptIL-6) inducing fluorescence quenching (OFF state) and a subsequent on-the-move affinity recognition of IL-6 from AptIL-6 (IL-6-AptIL-6 complex) recovering the fluorescence (ON state). An aptamer against IL-6 was selected and developed by the systematic evolution of ligands by exponential enrichment technology. This approach displayed a suitable linear range of 0.07-1000 pg mL-1 (r = 0.995) covering the cut-off and clinical practice levels, allowing direct determination without any dilution and simplifying the analysis as well as exhibiting an excellent sensitivity (LOD = 0.02 pg mL-1) in ultralow volumes of diagnostic clinical samples (2 μL). A high agreement between IL-6 levels obtained from our MM-based approach and the method used by the Hospital was obtained (relative error < 3%). The MM-based aptassay is competitive in comparison with that of the Hospital, in terms of a significant reduction of the sample volume (15 times less) and enhanced sensitivity, employing similar analysis times. These results position MM technology with enough potential to achieve high sensitivities in low sample volumes, opening new avenues in diagnosis based on low sample volumes.

Motion Analysis and Real‐Time Trajectory Prediction of Magnetically Steerable Catalytic Janus Micromotors

Chemically driven micromotors display unpredictable trajectories due to the rotational Brownian motion interacting with the surrounding fluid molecules. This hampers the practical applications of these tiny robots, particularly where precise control is a requisite. To overcome the rotational Brownian motion and increase motion directionality, robots are often decorated with a magnetic composition and guided by an external magnetic field. However, despite the straightforward method, explicit analysis and modeling of their motion have been limited. Here, catalytic Janus micromotors are fabricated with distinct magnetizations and a controlled self‐propelled motion with magnetic steering is shown. To analyze their dynamic behavior, a dynamic model that can successfully predict the trajectory of micromotors in uniform viscous flows in real time by incorporating a form of state‐dependent‐coefficient with a robust two‐stage Kalman filter is theoretically developed. A good agreement is observed between the theoretically predicted dynamics and experimental observations over a wide range of model parameter variations. The developed model can be universally adopted to various designs of catalytic micro‐/nanomotors with different sizes, geometries, and materials, even in diverse fuel solutions. Finally, the proposed model can be used as a platform for biosensing, detecting fuel concentration, or determining small‐scale motors’ propulsion mechanisms in an unknown environment.

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)byusing 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.

Micromachines for Microplastics Treatment.

The increasing accumulation of persistent nondegradable microplastics in the marine environment represents a global environmental problem. Among emerging approaches to tackle microplastics are micro- and nanomotors, tiny devices capable of autonomous propulsion powered by chemical fuels or light. These devices are capable of on-the-fly recognition, capture, and decomposition of pollutants. In the past, various micromotors were designed to efficiently remove and degrade soluble organic pollutants. Current effort is given to the rational design and surface functionalization to achieve micromotors capable of capturing, transporting, and releasing microplastics of different shapes and chemical structures. The catalytic micromotors performing photocatalysis and photo-Fenton chemistry hold great promise for the degradation of most common plastics. In this review, we highlight recent progress in the field of micromotors for microplastics treatment. These tiny self-propelled machines are expected to stimulate a quantum leap in environmental remediation.

Long-range hydrodynamic communication among synthetic self-propelled micromotors

Long-range communication is ubiquitous among living organisms, but it remains undiscovered among synthetic micro/nanomotors. Here, we report the long-range hydrodynamic communication among synthetic micromotors. With the high activities when powered by a mixed fuel of N2H4 and H2O2, catalytic micromotors move in a stable oblique head-down orientation and thus generate strong, steady converging phoretic flows near a substrate. Consequently, they can emit robust hydrodynamic signals to trigger neighboring motors within a long range and also initiate an “approach-hit-and-run” response when sensing the signals emitted from others. This hydrodynamic communication can be reciprocal or one-way, intraspecific or interspecific, spontaneous or controllable, and it widely exists in various catalytic micromotor systems. Utilizing the hydrodynamic signal, the micromotor can also act as a leader to gather small particles (followers) and exhibit a biomimetic competitive behavior against others for the followers. This work may facilitate the fabrication of intelligent micro/nanorobots for micromanipulations and biomimetic micro/nanorobotic systems.

Highly Efficient Active Colloids Driven by Galvanic Exchange Reactions.

Micromotors are propelled by a variety of chemical reactions, with most of them being of catalytic nature. There are, however, systems based on redox reactions, which show clear benefits for efficiency. Here, we broaden the spectrum of suitable reactions to galvanic exchange processes, or an electrochemical replacement of a solid metal layer with dissolved ionic species of a more noble metal. We study the details of motility and the influence of different reaction parameters to conclude that these galvanophoretic processes circumvent several steps that lose efficiency in catalytic micromotors. Furthermore, we investigate the chemical process, the charge, and flow conditions that lead to this highly efficient new type of active motility. Toward a better understanding of the underlying processes, we propose an electrokinetic model that we numerically solve via finite elements.

Active, Yet Little Mobility: Asymmetric Decomposition of H2O2 Is Not Sufficient in Propelling Catalytic Micromotors.

A popular principle in designing chemical micromachines is to take advantage of asymmetric chemical reactions such as the catalytic decomposition of H2O2. Contrary to intuition, we use Janus micromotors half-coated with platinum (Pt) or catalase as an example to show that this ingredient is not sufficient in powering a micromotor into self-propulsion. In particular, by annealing a thin Pt film on a SiO2 microsphere, the resulting microsphere half-decorated with discrete Pt nanoparticles swims ∼80% more slowly than its unannealed counterpart in H2O2, even though they both catalytically produce comparable amounts of oxygen. Similarly, SiO2 microspheres half-functionalized with the enzyme catalase show negligible self-propulsion despite high catalytic activity toward decomposing H2O2. In addition to highlighting how surface morphology of a catalytic cap enables/disables a chemical micromotor, this study offers a refreshed perspective in understanding how chemistry powers nano- and microscopic objects (or not): our results are consistent with a self-electrophoresis mechanism that emphasizes the electrochemical decomposition of H2O2 over nonelectrochemical pathways. More broadly, our finding is a critical piece of the puzzle in understanding and designing nano- and micromachines, in developing capable model systems of active colloids, and in relating enzymes to active matter.

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.

Switching Propulsion Mechanisms of Tubular Catalytic Micromotors.

Different propulsion mechanisms have been suggested for describing the motion of a variety of chemical micromotors, which have attracted great attention in the last decades due to their high efficiency and thrust force, enabling several applications in the fields of environmental remediation and biomedicine. Bubble-recoil based motion, in particular, has been modeled by three different phenomena: capillary forces, bubble growth, and bubble expulsion. However, these models have been suggested independently based on a single influencing factor (i.e., viscosity), limiting the understanding of the overall micromotor performance. Therefore, the combined effect of medium viscosity, surface tension, and fuel concentration is analyzed on the micromotor swimming ability, and the dominant propulsion mechanisms that describe its motion more accurately are identified. Using statistically relevant experimental data, a holistic theoretical model is proposed for bubble-propelled tubular catalytic micromotors that includes all three above-mentioned phenomena and provides deeper insights into their propulsion physics toward optimized geometries and experimental conditions.