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.

Boosting cisplatin chemotherapy by nanomotor-enhanced tumor penetration and DNA adducts formation

Despite many nano-based strategies devoted to delivering cisplatin for tumor therapy, its clinical benefits are compromised by poor tissue penetration and limited DNA adducts formation of the drug. Herein, a cisplatin loading nanomotor based janus structured Ag-polymer is developed for cisplatin delivery of deeper tissue and increased DNA adducts formation. The nanomotor displayed a self‐propelled tumor penetration fueled by hydrogen peroxide (H₂O₂) in tumor tissues, which is catalytically decomposed into a large amount of oxygen bubbles by Ag nanoparticles (NPs). Notably, cisplatin could elevate the intracellular H₂O₂ level through cascade reactions, further promote the degradation of Ag NPs accompanied with the Ag⁺ release, which could downregulate intracellular Cl⁻ through the formation of AgCl precipitate, thereby enhancing cisplatin dechlorination and Pt–DNA formation. Moreover, polymer can also inhibit the activity of ALKBH2 (a Fe²⁺-dependent DNA repair enzyme) by chelating intracellular Fe²⁺ to increase the proportion of irreparable Pt–DNA cross-links. It is found that deep tissue penetration, as well as the increased formation and maintenance of Pt–DNA adducts induced by the nanomotor afford 80% of tumor growth inhibition with negligible toxicity. This work provides an important perspective of resolving chemotherapeutic barriers for boosting cisplatin therapy.

Active matter dynamics in confined microfluidic environments

The field of active matter is a nascent area of research in soft condensed matter physics, which is drawing on the expertise of researchers from diverse disciplines. Small scale active particles-both inorganic and biological-display non-trivial emergent dynamics and interactions that could help us understand complex biological processes and phenomena. Recently, using microfluidic technologies, several research groups have performed important experimental and theoretical studies to understand the behavior of self-propelled particles and molecular active matter within confined environments-to glean a fundamental understanding of the cellular processes occurring under ultra-low Reynolds number conditions. In this chapter, we would like to review applications of microfluidics in active matter research, highlighting a few important theoretical and experimental investigations. We will conclude the discussion with a note on the future of this field mentioning a few open questions that are at the forefront of our minds.

Polymer Nanoparticles and Nanomotors Modified by DNA/RNA Aptamers and Antibodies in Targeted Therapy of Cancer

Polymer nanoparticles and nano/micromotors are novel nanostructures that are of increased interest especially in the diagnosis and therapy of cancer. These structures are modified by antibodies or nucleic acid aptamers and can recognize the cancer markers at the membrane of the cancer cells or in the intracellular side. They can serve as a cargo for targeted transport of drugs or nucleic acids in chemo- immuno- or gene therapy. The various mechanisms, such as enzyme, ultrasound, magnetic, electrical, or light, served as a driving force for nano/micromotors, allowing their transport into the cells. This review is focused on the recent achievements in the development of polymer nanoparticles and nano/micromotors modified by antibodies and nucleic acid aptamers. The methods of preparation of polymer nanoparticles, their structure and properties are provided together with those for synthesis and the application of nano/micromotors. The various mechanisms of the driving of nano/micromotors such as chemical, light, ultrasound, electric and magnetic fields are explained. The targeting drug delivery is based on the modification of nanostructures by receptors such as nucleic acid aptamers and antibodies. Special focus is therefore on the method of selection aptamers for recognition cancer markers as well as on the comparison of the properties of nucleic acid aptamers and antibodies. The methods of immobilization of aptamers at the nanoparticles and nano/micromotors are provided. Examples of applications of polymer nanoparticles and nano/micromotors in targeted delivery and in controlled drug release are presented. The future perspectives of biomimetic nanostructures in personalized nanomedicine are also discussed.

A practical guide to active colloids: choosing synthetic model systems for soft matter physics research

Synthetic active colloids that harvest energy stored in the environment and swim autonomously are a popular model system for active matter. This emerging field of research sits at the intersection of materials chemistry, soft matter physics, and engineering, and thus cross-talk among researchers from different backgrounds becomes critical yet difficult. To facilitate this interdisciplinary communication, and to help soft matter physicists with choosing the best model system for their research, we here present a tutorial review article that describes, in appropriate detail, six experimental systems of active colloids commonly found in the physics literature. For each type, we introduce their background, material synthesis and operating mechanisms and notable studies from the soft matter community, and comment on their respective advantages and limitations. In addition, the main features of each type of active colloid are summarized into two useful tables. As materials chemists and engineers, we intend for this article to serve as a practical guide, so those who are not familiar with the experimental aspects of active colloids can make more informed decisions and maximize their creativity.

Self-propelled cellulose nanocrystal based catalytic nanomotors for targeted hyperthermia and pollutant remediation applications

Inspired from biological motors, cellulose nanocrystals (CNCs) are strategically modified to induce self-propulsion behavior with the capabilities to catalytically degrade pollutants along with magnetic hyperthermia to clean arterial plaques during its course of propulsion. CNCs derived from renewable biomass, are decorated with catalytically active, magneto-responsive nanomaterials (Fe2O3/Pd nanoparticles) through sustainable routes. CNC nanomotors show improved propulsion at lowered peroxide concentrations with remotely controlled trajectory through chemo-magnetic field gradients and ideal surface-wettability characteristics, overcoming the requirement of surfactants, as with traditional nanomotors. We observed that nanomotors undergo motion through heterogeneous bubble propulsion mechanism, with capability to in situ degrade pollutants and generate local heat through hyperthermia, enhancing the rate of degradation process in real time. As proof of concept, we demonstrate that the dynamics of nanomotors can be controlled in a microfluidic channel through site-directed magnetic field and induction of pH gradient, mimicking the chemotaxis in cell-like environment and as swarm of nano-surgeons removes plaques from clogged arteries. Our study shows that strategic modification of CNCs results in fabrication of nanomotors with efficient propulsion system infused with multi-functional characteristics of high catalytic activity and magnetic hyperthermia which opens up new avenues for utilization of bio-based nanomotors derived from lignocellulose for myriad applications.

Delivery of magnetic micro/nanoparticles and magnetic-based drug/cargo into arterial flow for targeted therapy

Magnetic drug targeting (MDT) and magnetic-based drug/cargo delivery are emerging treatment methods which attracting the attention of many researchers for curing different cancers and artery diseases such as atherosclerosis. Herein, computational studies are accomplished by utilizing magnetic approaches for cancer and artery atherosclerosis drug delivery, including nanomagnetic drug delivery and magnetic-based drug/cargo delivery. For the first time, the four-layer structural model of the artery tissue and its porosity parameters are modeled in this study which enables the interaction of particles with the tissue walls in blood flow. The effects of parameters, including magnetic field strength (MFS), magnet size, particle size, the initial position of particles, and the relative magnetic permeability of particles, on the efficacy of MDT through the artery walls are characterized. The magnetic particle penetration into artery layers and fibrous cap (the covering layer over the inflamed part of the artery) is further simulated. The MDT in healthy and diseased arteries demonstrates that some of the particles stuck in these tissues due to the collision of particles or blood flow deviation in the vicinity of the inflamed part of the artery. Therefore the geometry of artery and porosity of its layers should be considered to show the real interaction of particles with the artery walls. Also, the results show that increasing the particles/drug/cargo size and MFS leads to more particles/drug/cargo retention within the tissue. The present work provides insights into the decisive factors in arterial MDT with an obvious impact on locoregional cancer treatment, tissue engineering, and regenerative medicine.

Nanoscale Biosensors Based on Self-Propelled Objects

This review provides a comprehensive overview of the latest developments (2016⁻2018 period) in the nano and micromotors field for biosensing applications. Nano and micromotor designs, functionalization, propulsion modes and transduction mechanism are described. A second important part of the review is devoted to novel in vitro and in vivo biosensing schemes. The potential and future prospect of such moving nanoscale biosensors are given in the conclusions.

Polymer platforms for micro- and nanomotor fabrication

Artificial, self-propelled micro- and nanomotors are small devices capable of autonomous movement, which are a powerful scientific innovation for solving various medical and environmental issues. Their design is frequently inspired by complex biological structures which are composed of biopolymers and their composites. The choice of materials for nano- and micromachines is crucial for their shape, mechanism and efficiency of propulsion. In this review, we discuss the utilization and fabrication of polymers as soft components of micro- and nanomotors.

Small-Scale Machines Driven by External Power Sources

Micro- and nanorobots have shown great potential for applications in various fields, including minimally invasive surgery, targeted therapy, cell manipulation, environmental monitoring, and water remediation. Recent progress in the design, fabrication, and operation of these miniaturized devices has greatly enhanced their versatility. In this report, the most recent progress on the manipulation of small-scale robots based on power sources, such as magnetic fields, light, acoustic waves, electric fields, thermal energy, or combinations of these, is surveyed. The design and propulsion mechanism of micro- and nanorobots are the focus of this article. Their fabrication and applications are also briefly discussed.

Biosensing Strategy for Simultaneous and Accurate Quantitative Analysis of Mycotoxins in Food Samples Using Unmodified Graphene Micromotors

A high-performance graphene-based micromotor strategy for simultaneous, fast, and reliable assessment of two highly concerning mycotoxins (fumonisin B1 (FB1) and ocratoxin A (OTA)) has successfully been developed. The assay principle is based on the selective recognition from aptamers to the target mycotoxins and further "on-the-move" fluorescence quenching of the free aptamer in the outer layer of unmodified reduced graphene (rGO; sensing layer) micromotors. Template-prepared rGO/platinum nanoparticles (PtNPs) tubular micromotors were synthesized rapidly and inexpensively by the direct electrodeposition within the conical pores of a polycarbonate template membrane. The new wash-free approach offers using just 1 μL of sample, a simultaneous and rapid "on-the-fly" detection (2 min) with high sensitivity (limits of detection of 7 and 0.4 ng/mL for OTA and FB1, respectively), and high selectivity. Remarkable accuracy (E_r < 5%) during the mycotoxin determination in certified reference material as well as excellent quantitative recoveries (96-98%) during the analysis of food samples were also obtained. The excellent results obtained allow envisioning an exciting future for the development of novel applications of catalytic micromotors in unexplored fields such as food safety diagnosis.

Internally/Externally Bubble-Propelled Photocatalytic Tubular Nanomotors for Efficient Water Cleaning

We describe a highly effective bubble-propelled nanomotor for the photocatalytic decomposition of organic pollutants in water. Two different tubular TiO₂ nanomotor systems are presented: one with Pt nanoparticles decorated on the inner surface and the other with Pt nanoparticles decorated on the outer surface. This is the first time that we have observed the autonomous movement of a tubular nanomotor without the aid of any surfactant, as well as a tubular nanomotor externally decorated with Pt propelled by oxygen bubbles. The synergy between the Pt nanoparticles and the superhydrophilic wetting behavior of the TiO₂ nanotubes endows the two nanomotor systems with high speed at very low H₂O₂ fuel concentrations without the addition of any surfactant. The efficient photodecomposition of rhodamine B demonstrates the intermixing and photocatalytic ability of the two nanomotor systems, which opens new avenues for the development of multifunctional bubble-propelled micro/nanomotors with myriad practical applications.

Labs-on-a-chip meet self-propelled micromotors

This frontier review covers recent advances in the field of nanomaterial-based micromotors for the development of novel labs-on-a-chip (LOCs). In this review, we will discuss how carbon nanomaterials "on-board" of micromotors offer particular promise for diverse LOC applications. New trends in the field, directed towards the use of quantum dots and nanoparticles as functional materials for sophisticated micromotors, will be reviewed. Micromotor strategies using functionalized catalytic microengines to capture and transport (bio)molecules between the different reservoirs of LOC devices will also be covered. These recent advances are bringing closer our hopes for personalized medicine and food safety assurance, among others.

From Nanomotors to Micromotors: The Influence of the Size of an Autonomous Bubble-Propelled Device upon Its Motion

Synthetic autonomously moving nano and micromotors are in the forefront of nanotechnology. Different sizes of nano and micromotors have been prepared, but the systematic study of the influence of their sizes on motion is lacking. We synthesized different sizes of tubular micro/nanomotors by membrane template-assisted electrodeposition. The influence of dimensions on the dynamics of micro/nanotubes was studied at a significantly reduced scale than rolled-up microtubes, down to the nanometer regime. Both the geometric parameters and the chemical environment can affect the dynamics of micro/nanotubes. The bubble size and ejection frequency were investigated in correlation with the velocity of micro/nanotubes. The comparison between different sizes of micro/nanotubes showed that geometric parameters of micro/nanotubes will influence the velocity of micro/nanotubes at moderate fuel concentrations. Furthermore, it also affects the activity of micro/nanotubes at low fuel concentrations and imposes limitations on the velocity at very high fuel concentrations. Nanotubes with nanometer-sized openings need a higher concentration of H2O2 to be activated. Larger tubes can possess a higher absolute value of velocity than smaller tubes, but do not necessarily have a higher velocity by body lengths per unit time. Insight into bubble ejection/propulsion cycle is also provided. The results presented here provide important implications for the consideration of dimensions in the fabrication of tubular micro/nanomotors.

Template Electrosynthesis of High-Performance Graphene Microengines

Template-prepared graphene/Pt and graphene/Au tubular microengines, with extremely high electrocatalytic activity and propulsion efficiency, are described. The new bubble-propelled graphene/metal micromotors are synthesized rapidly and inexpensively by the direct electrodeposition of graphene oxide (GO) within the conical pores of a polycarbonate template membrane followed by deposition of the inner metal layer. The presence of high number of edges and defects in the graphene layer results in highly reactive microporous Pt or Au catalytic structures. The high catalytic activity leads to an ultrafast bubble propulsion (as high as 170 body lengths/sec) and operation at extremely low levels (0.1%) of the peroxide fuel. The effect of such dramatically enhanced catalytic surface area on the bubble growth and motor speed has been theoretically modeled. The template-prepared graphene-based microengines display distinct moving trajectories, along with long microbubble tails. The fast catalytic locomotion and attractive performance of the new graphene/Pt micromotors hold considerable promise for diverse applications.

Magneto-Acoustic Hybrid Nanomotor

Efficient and controlled nanoscale propulsion in harsh environments requires careful design and manufacturing of nanomachines, which can harvest and translate the propelling forces with high spatial and time resolution. Here we report a new class of artificial nanomachine, named magneto-acoustic hybrid nanomotor, which displays efficient propulsion in the presence of either magnetic or acoustic fields without adding any chemical fuel. These fuel-free hybrid nanomotors, which comprise a magnetic helical structure and a concave nanorod end, are synthesized using a template-assisted electrochemical deposition process followed by segment-selective chemical etching. Dynamic switching of the propulsion mode with reversal of the movement direction and digital speed regulation are demonstrated on a single nanovehicle. These hybrid nanomotors exhibit a diverse biomimetic collective behavior, including stable aggregation, swarm motion, and swarm vortex, triggered in response to different field inputs. Such adaptive hybrid operation and controlled collective behavior hold considerable promise for designing smart nanovehicles that autonomously reconfigure their operation mode according to their mission or in response to changes in their surrounding environment or in their own performance, thus holding considerable promise for diverse practical biomedical applications of fuel-free nanomachines.

Template electrosynthesis of tailored-made helical nanoswimmers

We demonstrate a template electrosynthesis for large-scale low-cost preparation of remarkably small magnetically driven tailored-made helical nanoswimmers that display efficient propulsion behavior and hold considerable promise for future miniature devices in the human body.

Synthesis and characterization of Ag-Co-Ni nanowires

This work provides an electrodeposition-based methodology for synthesizing multicomponent nanowires containing Ag, Co and Ni atoms. Nanowire morphology was obtained by using an anodic alumina membrane with cylindrical pores of ∼ 200-nm diameter. Structural, compositional and magnetic characterization revealed that the as-synthesized nanowires adopted a core-shell microstructure. The core (axial region) contained pure Ag phase volumes with a plate-like morphology oriented perpendicular to the nanowire axis. The shell (peripheral region) contained pure Ag nanoparticles along with superparamagnetic Co and Ni rich clusters.

Asymmetric van der Waals forces drive orientation of compositionally anisotropic nanocylinders within smectic arrays: experiment and simulation

Understanding how micro- and nanoparticles interact is important for achieving bottom-up assembly of desired structures. Here, we examine the self-assembly of two-component, compositionally asymmetric nanocylinders that sediment from solution onto a solid surface. These particles spontaneously formed smectic arrays. Within the rows of an array, nanocylinders tended to assemble such that neighboring particles had the same orientation of their segments. As a probe of interparticle interactions, we classified nanocylinder alignments by measuring the segment orientations of many sets of neighboring particles. Monte Carlo simulations incorporating an exact expression for the van der Waals (vdW) energy indicate that differences in the vdW interactions, even when small, are the key factor in producing observed segment alignment. These results point to asymmetrical vdW interactions as a potentially powerful means of controlling orientation in multicomponent cylinder arrays, and suggest that designing for these interactions could yield new ways to control self-assembly.