Magnetic Micromotors Research Articles

Magnetic Micromotors with Spiky Gold Nanoshells as SERS Sensors for Thiram and Bacteria Detection.

Surface-enhanced Raman scattering (SERS) is widely used in all kinds of detection due to its ultrahigh sensitivity and selectivity. Micromotors, when used as SERS sensors, or the so-called "hotspots on the fly", can combine both controlled mobility and SERS sensing capacity, and are ideal for versatile in situ detection. In this work, mobile SERS sensors are successfully fabricated by growing gold nanospikes onto magnetic microsphere surfaces. These mobile micromotors can act as normal SERS sensors, characterized by the trace detection of thiram, a highly toxic fungicide. The detection limit can reach 0.1nM, as good as most other noble metal deposited substrates. With significant magnetic gradient forces, separation of pathogenic bacteria from bulk solution is achieved once these magnetic micromotors bind with bacterial cells. Manipulated propulsion of micromotors, on the other hand, enables them to approach and contact pathogenic bacterial cells on command and further acquire Raman spectra under a controlled degree of contact, a capability never seen with passive sensors. The robotic SERS sensors have demonstrated unique sensing characteristics with controlled manipulations along with discriminative detection between bacterial species.

Droplet manipulation in liquid flow using of magnetic micromotors for drug delivery and microfluidic systems

The task of droplet manipulation is of great practical importance in such areas as biochemistry, drug delivery and microfluidic systems. Here we demonstrate a method for controlling the movement of droplets in an oil-in-water emulsion flow using magnetic nanoparticles (MNPs). A distinctive feature of this method is that the MNPs are not dispersed within droplets but in the continuous phase of the emulsion. Due to this, after the droplet manipulation procedure is completed, the MNPs can be easily removed from the emulsion without destroying the droplets. This method represents an innovative alternative to the previously known methods. The MNPs can be used to change the speed and direction of droplet movement in a liquid flow. If the magnetic field gradient is directed against the liquid flow, and the flow velocity is less than a certain critical value, then with help of a magnetic field it is possible to move droplets against the liquid flow. The ability to control the movement of droplets in a flow largely depends on the surface wettability of the MNPs. Hydrophobic MNPs are adsorbed on the surface of droplets and move with them in a magnetic field. If the magnetic field gradient is directed along the liquid flow, this leads to an increase in the droplet speed. In the case of using hydrophilic MNPs, the influence of the magnetic field on the droplet speed in the flow turns out to be ambiguous. These results can provide a basis for the development of magnetic droplet-based drug delivery systems.

Synthesis of carbon dot LDHs@MnO2 tubular magnetic micromotors for detection and degradation of oxytetracycline

Antibiotic residues in water are closely related to human health and environment. Therefore, it is of great significance to detect and remove antibiotics in water. Here, by integrating nanozyme activity and self-propelled movement that can promote the mass transfer and diffusion in solution, a novel dual-functional CDs-LDHs@MnO2/Fe3O4 magnetic micromotor with high exposed active sites for the detection and removal of oxytetracycline (OTC) was prepared by a biotemplate method. The micromotor could move autonomously in aqueous solution containing H2O2, reaching a mean speed of 158.35 ± 11.64 μm/s in 5 wt% H2O2. Due to the synergy of motion and the CDs-enhanced peroxidase-like activity, the micromotor could easily detect OTC in aqueous solution with a low detection limit (0.291 μM), wide detection range (0–100 μM), high selectivity, and a high magnetic recovery rate (near 85 %). More importantly, these micromotors also enabled rapid degradation of OTC through Fenton and Fenton-like reactions, reaching 87.93 % in the presence of 5 wt% H2O2. This work could provide a new idea for detecting and removing antibiotics from water.

A novel bio-template route to synthesize enzyme-immobilized MOF/LDH tubular magnetic micromotors and their application in water treatment

A ramie-templated micromotor loaded with a natural HRP enzyme was constructed, which had a potent peroxidase-like activity driven by decomposition of H2O2 for sensitive detection and degradation of catechol.

Helical magnetic micromotors decorated with nickel ferrocyanide for the active and rapid adsorption of radiocesium in water

Separating radioactive cesium from nuclear waste and contaminated environments is critical to mitigate radiological hazards. In response to this need, remote-controllable and Cs-selective micromotor adsorbents have been considered as a promising technology for rapid in-situ cleanup while minimizing secondary waste and radiation exposure to workers. In this study, we demonstrate the active and rapid removal of a radioactive contaminant from water by leveraging the magnetic manipulation capabilities of a helical and magnetic Ni micromotor coated with Cs-selective nickel ferrocyanide (NiFC). The use of polyvinyl alcohol fibers as a template enables the straightforward preparation of the helical wire structure, allowing for precise control over the diameter and pitch of the helix through simple twisting with Ni wires. By harnessing Ni2+ ions eluted from the Ni micromotor in an acid solution, we successfully fabricate NiFC-coated Ni (NiFC/Ni) micromotors that exhibit a selective removal efficiency greater than 98% for 137Cs, even in the presence of high concentrations of competing Na+ ions. Under the influence of an external magnetic field, the NiFC/Ni micromotor demonstrates rapid motion, achieving a pulling motion (100 body lengths per second) through a magnetic gradient and a tumbling motion (46 body lengths per second) induced by a rotating magnetic field. The tumbling motion of the NiFC/Ni micromotor substantially improves the Cs adsorption rate, resulting in a rate that surpasses that achieved under nonmoving conditions by a factor of 21. This improved adsorption rate highlights the considerable potential of magnetically manipulated micromotor self-propulsion for efficient water-pollution treatment.

Spatial Patterning of Micromotor Aggregation and Flux.

Using a spatially varying light pattern with light activated semi-conductor based magnetic TiO2 micromotors, we study the difference in micromotor flux between illuminated and non-illuminated regions in the presence and absence of an applied magnetic field. We find that the magnetic field enhances the flux of the motors which we attribute to a straightening of the micromotor trajectories which decreases the time they spend in the illuminated region. We also demonstrate spatially patterned light-induced aggregation of the micromotors and study its time evolution at various micromotor concentrations. Although light induced aggregation has been observed previously, spatial patterning of aggregation demonstrates a further means of control which could be relevant to swarm control or self-assembly applications. Overall, these results draw attention to the effect of trajectory shape on the flux of active colloids as well as the concentration dependence of aggregation and its time dependence within a spatially patterned region, which is not only pertinent to self-assembly and swarm control, but also provides insight into the behavior of active matter systems with spatially varying activity levels.

Self-propelled Janus magnetic micromotors as peroxidase-like nanozyme for colorimetric detection and removal of hydroquinone

A Janus micromotor-assisted dual-function platform through a novel and facile method was designed and fabricated for sensitive detection and rapid degradation of hydroquinone in water.

Synthesis of dual function Fe3O4@MnO2@HKUST-1 magnetic micromotors for efficient colorimetric detection and degradation of hydroquinone

A novel and simple strategy was applied for designing and fabricating a micromotor-assisted dual-functional platform for sensitive detection and rapid degradation of hydroquinone in water.

Micromotor-Assisted Keratinocytes Migration in a Floating Paper Chip.

In vitro epidermis models are important to evaluate and study disease progression and possible dermal drug delivery. An in vitro epidermis model using floating paper chips as a scaffold for proliferation and differentiation of primary human keratinocytes is reported. The formation of the four main layers of the epidermis (i.e., basal, spinosum, granulose, and cornified layers) is confirmed. The development of a cornified layer and the tight junction formation are evaluated as well as the alterations of organelles during the differentiation process. Further, this in vitro model is used to assess keratinocyte migration. Finally, magnetic micromotors are assembled, and their ability to aid cell migration on paper chips is confirmed when a static magnetic field is present. Taken together, this attempt to combine bottom-up synthetic biology with dermatology offers interesting opportunities for studying skin disease pathologies and evaluate possible treatments.

Ion-imprinted MnO2/CoFe2O4 Janus magnetic micromotors synthesized by a lotus pollen template for highly selective recognition and capture of Pb(ii) ions

A new strategy for the design and fabrication of a biomass-based micromotor for highly selective removal of metal contaminating ions from water.

Droplet-Based Microfluidic Preparation of Shape-Variable Alginate Hydrogel Magnetic Micromotors.

This article introduces a facile droplet-based microfluidic method for the preparation of Fe3O4-incorporated alginate hydrogel magnetic micromotors with variable shapes. By using droplet-based microfluidics and water diffusion, monodisperse (quasi-)spherical microparticles of sodium alginate and Fe3O4 (Na-Alg/Fe3O4) are obtained. The diameter varies from 31.9 to 102.7 µm with the initial concentration of Na-Alginate in dispersed fluid ranging from 0.09 to 9 mg/mL. Calcium chloride (CaCl2) is used for gelation, immediately transforming Na-Alg/Fe3O4 microparticles into Ca-Alginate hydrogel microparticles incorporating Fe3O4 nanoparticles, i.e., Ca-Alg/Fe3O4 micromotors. Spherical, droplet-like, and worm-like shapes are yielded depending on the concentration of CaCl2, which is explained by crosslinking and anisotropic swelling during the gelation. The locomotion of Ca-Alg/Fe3O4 micromotors is activated by applying external magnetic fields. Under the rotating magnetic field (5 mT, 1–15 Hz), spherical Ca-Alg/Fe3O4 micromotors exhibit an average advancing velocity up to 158.2 ± 8.6 µm/s, whereas worm-like Ca-Alg/Fe3O4 micromotors could be rotated for potential advancing. Under the magnetic field gradient (3 T/m), droplet-like Ca-Alg/Fe3O4 micromotors are pulled forward with the average velocity of 70.7 ± 2.8 µm/s. This article provides an inspiring and timesaving approach for the preparation of shape-variable hydrogel micromotors without using complex patterns or sophisticated facilities, which holds potential for biomedical applications such as targeted drug delivery.

Modular Interfacial Microswimmers

The transport of microscale matter suspended in a viscous fluid under confined conditions is essential in a wide range of fields and applications, including drug delivery and the study of dynamic self-assembly and constrained dynamics. Designing sophisticated, modular swimmers with different functional units and cooperative dynamic responses enables more complex tasks. In this work, dynamic self-assemblies exploring different transport mechanisms are guided with high maneuverability along a fluid interface. These magnetic micromotors, which do $n\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}t$ swim via capillary or Marangoni effects, could be used for precise, targeted interfacial transport of drugs under biological conditions.

Locomotion of micromotors in paper chips.

Locomotion of nano/micromotors in non-aqueous environments remains a challenging task. We assembled magnetic micromotors with different surface coatings and explored their locomotion in paper chips. Poly(L-lysine) deposition resulted in positively charged micromotors. Immobilized cellulase was used to increase the micromotors' paper penetration depth while a polyethylene glycol (PEG) coating was employed to limit the interaction between the micromotors and the cellulose fibers. All micromotors were able to move in the top layers of the paper chips with velocities dependent on the magnetic forces used to induce their locomotion, their sizes and the types of employed paper chips. Maximum speeds of up to ∼25 μm s-1 were observed for PEGylated micromotors in the fibrous cellulose environment. This type of micromotors has the potential to be considered in the area of paper microfluidics to facilitate distribution, or collection of moieties for biosensing or cell culture.

Investigating the Dynamics of the Magnetic Micromotors in Human Blood.

The field of micromotors has been growing exponentially with increased emphasis on biomedical applications, with various in vivo demonstrations of targeted drug delivery, biosensing, and gene delivery, among others. In parallel, these micromotors have been recently used for probing the rheological properties of both intra- and extracellular environments. Here, we demonstrate the application of magnetic micromotors for investigation of rheological properties of human blood. While there are several techniques to sense mechanical properties of blood, such as deformability of the red blood cells, this is the first experimental observation of using micromotors for these biophysical investigations. We hope that this will lead to a better understanding of the nature of interactions of micromotors with biological systems and expand the scope of micromotors for probing other related systems, such as interstitial fluids and other complex biological fluids.

A Rotating Spiral Micromotor for Noninvasive Zygote Transfer.

Embryo transfer (ET) is a decisive step in the in vitro fertilization process. In most cases, the embryo is transferred to the uterus after several days of in vitro culture. Although studies have identified the beneficial effects of ET on proper embryo development in the earlier stages, this strategy is compromised by the necessity to transfer early embryos (zygotes) back to the fallopian tube instead of the uterus, which requires a more invasive, laparoscopic procedure, termed zygote intrafallopian transfer (ZIFT). Magnetic micromotors offer the possibility to mitigate such surgical interventions, as they have the potential to transport and deliver cellular cargo such as zygotes through the uterus and fallopian tube noninvasively, actuated by an externally applied rotating magnetic field. This study presents the capture, transport, and release of bovine and murine zygotes using two types of magnetic micropropellers, helix and spiral. Although helices represent an established micromotor architecture, spirals surpass them in terms of motion performance and with their ability to reliably capture and secure the cargo during both motion and transfer between different environments. Herein, this is demonstrated with murine oocytes/zygotes as the cargo; this is the first step toward the application of noninvasive, magnetic micromotor‐assisted ZIFT.

Magnetic Micromotors for Multiple Motile Sperm Cells Capture, Transport, and Enzymatic Release

AbstractAn integrated system combining a magnetically‐driven micromotor and a synthetized protein‐based hyaluronic acid (HA) microflake is presented for the in situ selection and transport of multiple motile sperm cells (ca. 50). The system appeals for targeted sperm delivery in the reproductive system to assist fertilization or to deliver drugs. The binding mechanism between the HA microflake and sperm relies on the interactions between HA and the corresponding sperm HA receptors. Once sperm are captured within the HA microflake, the assembly is trapped and transported by a magnetically‐driven helical microcarrier. The trapping of the sperm‐microflake occurs by a local vortex induced by the microcarrier during rotation‐translation under a rotating magnetic field. After transport, the microflake is enzymatically hydrolyzed by local proteases, allowing sperm to escape and finally reach the target location. This cargo‐delivery system represents a new concept to transport not only multiple motile sperm but also other actively moving biological cargoes.

Magnetic Micromotors for Multiple Motile Sperm Cells Capture, Transport, and Enzymatic Release.

An integrated system combining a magnetically‐driven micromotor and a synthetized protein‐based hyaluronic acid (HA) microflake is presented for the in situ selection and transport of multiple motile sperm cells (ca. 50). The system appeals for targeted sperm delivery in the reproductive system to assist fertilization or to deliver drugs. The binding mechanism between the HA microflake and sperm relies on the interactions between HA and the corresponding sperm HA receptors. Once sperm are captured within the HA microflake, the assembly is trapped and transported by a magnetically‐driven helical microcarrier. The trapping of the sperm‐microflake occurs by a local vortex induced by the microcarrier during rotation‐translation under a rotating magnetic field. After transport, the microflake is enzymatically hydrolyzed by local proteases, allowing sperm to escape and finally reach the target location. This cargo‐delivery system represents a new concept to transport not only multiple motile sperm but also other actively moving biological cargoes.

APPLICATIONS OF UV-LIGA AND GRAYSCALE LITHOGRAPHY FOR DISPLAY TECHNOLOGIES

In the article MEMS technologies for display production and application presented. UV-LIGA and greyscale lithography based on SU-8 resist approaches were shown. Methods, technologies and structures of heterogeneous materials with soft magnetic properties, pros and cons are discussed. Unique specific parameters of soft magnetic composite material were achieved: magnetic induction of saturation – 2,1 Т, working frequency range – up to 1 MHz, permeability – up to 3000, total loss – 8 W/kg, Curie temperature – above 800 ºС. Electroplating allows deposition of soft magnetic alloys on the conductive substrate. Metals like Fe, Ni, Co with additives like B, P were used to get the best soft magnetic properties. Special codeposition process was developed to allow insertion of soft magnetic composite powder filaments into soft magnetic matrix formed during. It allows developing magnetic micromotors for display production. Simulation of the hybrid step micromotors was carried out in Ansys Maxwell 19. It was demonstrated that it is possible to get 10 mN m tourqe under 25 μm rotor-stator air gap. Only presented microtechnologies can provide such accuracy of the mciromotors elements. As for greyscale photolithography, special grey mask were developed and it was demonstrated the possibility to produce controllable real 3D relief on the SU-8 photoresist. Thus, microtechnologies should be integrated into display technology to provide cost effective production and advanced properties of final products.

Bioinspired zeolitic imidazolate framework (ZIF-8) magnetic micromotors for highly efficient removal of organic pollutants from water

This paper reports the first proof-of-concept of using bioinspired ZIF-8 based micromotors for efficient water remediation. Natural kapok fibers have unique hollow structure that contains cellulose and lignin, inspiring the design and fabrication of bubble-driving tubular micromotors as an active self-propelled micromachine for the removal of organic pollutants from water. The outer dense ZIF-8 layer can adsorb organic pollutants on the micromotors, and the inner catalyst acts as the engine decomposing fuel H2O2 for providing bubble propulsion. The magnetic γ-Fe2O3 enables the external magnetic control movement and recovery of micromotors. The maximum adsorption capacity of ZIF-8-based magnetic micromotors toward Congo red and doxycycline were high as 394 and 242 mg g−1, respectively, mainly due to the enhanced micromotor-pollutant contacts by their autonomous motion and the resulting mixing associated effect. This novel ZIF-8 micromotor also showed outstanding stability and reusability in aqueous solution, indicating that their great potential for future application in water treatment.

Electrochemically synthesized nanostructures for the manipulation of cells: Biohybrid micromotors

In this communication we describe the preparation and operation of two types of Ni/Au nanorods (NRs) as new magnetic micromotors for the transport and manipulation of single cells to target specific areas with micron-size precision. This enables huge potential environmental or biomedical applications at the cellular scale. Electrodeposition followed by chemical treatment was employed to fabricate biocompatible Ni/Au NRs in two different configurations: non-homogeneous bi-segmented Ni@NiO–Au and homogeneous core-shell Ni@Au NRs. After incubating the NRs with yeast cells for 24h, they were partially taken into the cells, forming cells–NR biohybrid microstructures. We demonstrate that the asymmetric hybrid structures can be driven by external magnetic fields. The velocity and direction of the cells' motion can be controlled and tuned by modifying the field strength, frequency or direction of the rotating magnetic field. Similar hydrodynamic behaviour is observed for biohybrid microstructures containing the two types of NRs.