Trapping and detecting nanoplastics by MXene-derived oxide microrobots.

Nanoplastic pollution, the final product of plastic waste fragmentation in the environment, represents an increasing concern for the scientific community due to the easier diffusion and higher hazard associated with their small sizes. Therefore, there is a pressing demand for effective strategies to quantify and remove nanoplastics in wastewater. This work presents the "on-the-fly" capture of nanoplastics in the three-dimensional (3D) space by multifunctional MXene-derived oxide microrobots and their further detection. A thermal annealing process is used to convert Ti3C2Tx MXene into photocatalytic multi-layered TiO2, followed by the deposition of a Pt layer and the decoration with magnetic γ-Fe2O3 nanoparticles. The MXene-derived γ-Fe2O3/Pt/TiO2 microrobots show negative photogravitaxis, resulting in a powerful fuel-free motion with six degrees of freedom under light irradiation. Owing to the unique combination of self-propulsion and programmable Zeta potential, the microrobots can quickly attract and trap nanoplastics on their surface, including the slits between multi-layer stacks, allowing their magnetic collection. Utilized as self-motile preconcentration platforms, they enable nanoplastics' electrochemical detection using low-cost and portable electrodes. This proof-of-concept study paves the way toward the "on-site" screening of nanoplastics in water and its successive remediation.

Collective behavior of magnetic microrobots through immuno-sandwich assay: On-the-fly COVID-19 sensing.

Mobile self-propelled micro/nanorobots are mobile binding surface that improved the sensitivity of many biosensing system by "on-the-fly" identification and isolation of different biotargets. Proteins are powerful tools to predict infectious disease progression such as COVID-19. The main methodology used to COVID-19 detection is based on ELISA test by antibodies detection assays targeting SARS-CoV-2 virus spike protein and nucleocapside protein that represent an indirect SARS-CoV-2 detection with low sentitivy and specificity. Moreover ELISA test are limited to used external shaker to obtain homogenously immobilization of antibodies and protein on sensing platform. Here, we present magnetic microrobots that collective self-assembly through immuno-sandwich assay and they can be used as mobile platform to detect on-the-fly SARS-CoV-2 virus particle by its spike protein. The collective self-assembly of magnetic microrobots through immuno-sandwich assay enhanced its analytical performance in terms of sensitivity decreasing the detection limit of SARS-CoV-2 virus by one order of magnitude with respect to the devices previously reported. This proof-of-concept of microrobotics offer new ways to the detection of viruses and proteins of medical interest in general.

Efficient Protein Transfection by Swarms of Chemically Powered Plasmonic Virus-Sized Nanorobots.

Transfection is based on nonviral delivery of nucleic acids or proteins into cells. Viral approaches are being used; nevertheless, their translational capacity is nowadays decreasing due to persistent fear of their safety, therefore creating space for the field of nanotechnology. However, nanomedical approaches introducing static nanoparticles for the delivery of biologically active molecules are very likely to be overshadowed by the vast potential of nanorobotics. We hereby present a rapid nonviral transfection of protein into a difficult-to-transfect prostate cancer cell line facilitated by chemically powered rectangular virus-sized (68 nm × 33 nm) nanorobots. The enhanced diffusion of these biocompatible nanorobots is the key to their fast internalization into cells, happening in a matter of minutes and being up to 6-fold more efficient compared to static nanorobots in a nonfueled environment. The Au/Ag plasmonic nature of these nanorobots makes them simply traceable and allows for their detailed subcellular localization. Protein transfection mediated by such nanorobots is an important step forward, challenging the field of nanomedicine and having potential in future translational medical research.

The Effect of Chemical Structure of OEG Ligand Shells with Quaternary Ammonium Moiety on the Colloidal Stabilization, Cellular Uptake and Photothermal Stability of Gold Nanorods.

PURPOSE: Plasmonic photothermal cancer therapy by gold nanorods (GNRs) emerges as a promising tool for cancer treatment. The goal of this study was to design cationic oligoethylene glycol (OEG) compounds varying in hydrophobicity and molecular electrostatic potential as ligand shells of GNRs. Three series of ligands with different length of OEG chain (ethylene glycol units = 3, 4, 5) and variants of quaternary ammonium salts (QAS) as terminal functional group were synthesized and compared to a prototypical quaternary ammonium ligand with alkyl chain - (16-mercaptohexadecyl)trimethylammonium bromide (MTAB). METHODS: Step-by-step research approach starting with the preparation of compounds characterized by NMR and HRMS spectra, GNRs ligand exchange evaluation through characterization of cytotoxicity and GNRs cellular uptake was used. A method quantifying the reshaping of GNRs was applied to determine the effect of ligand structure on the heat transport from GNRs under fs-laser irradiation. RESULTS: Fourteen out of 18 synthesized OEG compounds successfully stabilized GNRs in the water. The colloidal stability of prepared GNRs in the cell culture medium decreased with the number of OEG units. In contrast, the cellular uptake of OEG+GNRs by HeLa cells increased with the length of OEG chain while the structure of the QAS group showed a minor role. Compared to MTAB, more hydrophilic OEG compounds exhibited nearly two order of magnitude lower cytotoxicity in free state and provided efficient cellular uptake of GNRs close to the level of MTAB. Regarding photothermal properties, OEG compounds evoked the photothermal reshaping of GNRs at lower peak fluence (14.8 mJ/cm2) of femtosecond laser irradiation than the alkanethiol MTAB. CONCLUSION: OEG+GNRs appear to be optimal for clinical applications with systemic administration of NPs not-requiring irradiation at high laser intensity such as drug delivery and photothermal therapy inducing apoptosis.

Smartdust 3D-Printed Graphene-Based Al/Ga Robots for Photocatalytic Degradation of Explosives.

Milli/micro/nanorobots are considered smart devices able to convert energy taken from different sources into mechanical movement and accomplish the appointed tasks. Future advances and realization of these tiny devices are mostly limited by the narrow window of material choices, the fuel requirement, multistep surface functionalization, rational structural design, and propulsion ability in complex environments. All these aspects call for intensive improvements that may speed up the real application of such miniaturized robots. 3D-printed graphene-based smartdust robots provided with a magnetic response and filled with aluminum/gallium molten alloy (Al/Ga) for autonomous motion are presented. These robots can swim by reacting with the surrounding environment without adding any fuel. Because their outer surface is coated with a hydrogel/photocatalyst (chitosan/carbon nitride, C3 N4 ) layer, these robots are used for the photocatalytic degradation of the picric acid as an explosive model molecule under visible light. The results show a fast and efficient degradation of picric acid that is attributed to a synergistic effect between the adsorption capability of the chitosan and the photocatalytic activity of C3 N4 particles. This work provides added insight into the large-scale fabrication, easy functionalization, and propulsion of tiny robots for environmental applications.

Cancer Cells Microsurgery via Asymmetric Bent Surface Au/Ag/Ni Microrobotic Scalpels Through a Transversal Rotating Magnetic Field.

The actuation of micro/nanomachines by means of a magnetic field is a promising fuel-free way to transport cargo in microscale dimensions. This type of movement has been extensively studied for a variety of micro/nanomachine designs, and a special magnetic field configuration results in a near-surface walking. We developed "walking" micromachines which transversally move in a magnetic field, and we used them as microrobotic scalpels to enter and exit an individual cancer cell and cut a small cellular fragment. In these microscalpels, the center of mass lies approximately in the middle of their length. The microrobotic scalpels show good propulsion efficiency and high step-out frequencies of the magnetic field. Au/Ag/Ni microrobotic scalpels controlled by a transversal rotating magnetic field can enter the cytoplasm of cancer cells and also are able to remove a piece of the cytosol while leaving the cytoplasmic membrane intact in a microsurgery-like manner. We believe that this concept can be further developed for potential biological or medical applications.

A highly sensitive enzyme-less glucose sensor based on pnictogens and silver shell-gold core nanorod composites.

Herein, we successfully incorporated pnictogen-Au@AgNR composites, produced by mixing shear exfoliated pnictogen nanosheets with silver shell, gold core nanorods (Au@AgNRs), as novel electrode materials towards the development of a non-enzymatic electrochemical glucose sensor. The findings of this study conceptually prove the feasibility of incorporating pnictogen-based composites for future development of electrochemical sensors.

Confined Bubble-Propelled Microswimmers in Capillaries: Wall Effect, Fuel Deprivation, and Exhaust Product Excess.

Self-propelled autonomous nano/microswimmers are at the forefront of materials science. These swimmers are expected to operate in highly confined environments, such as between the grains of soil or in the capillaries of the human organism. To date, little attention is paid to the problem that in such a confined environment the fuel powering catalytic nano/microswimmers can be exhausted quickly and the space can be polluted with the product of the catalytic reaction. In addition, the motion of the nano/microswimmers may be influenced by the confinement. These issues are addressed here, showing the influence of the size of the capillary and length of the micromotor on the motion and the influence of the depletion of the fuel and excess of the exhaust products. Theoretical modeling is provided as well to bring further insight into the observations. This article shows challenges that these systems face and stimulates research to overcome them.

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.

Preserving Fine Structure Details and Dramatically Enhancing Electron Transfer Rates in Graphene 3D-Printed Electrodes via Thermal Annealing: Toward Nitroaromatic Explosives Sensing.

Additive manufacturing (AM) represents one of the nine pillars of the new industrial revolution. Owing to the enthusiastic utilization of this technology by the wider professional and amateur communities, AM is becoming a driving force in the manufacturing sector due to its fast expansion and the availability of cheap and robust 3D printers. The 3D printing, especially the fused deposition modeling (FDM) method, has previously been utilized to fabricate carbon/polylactic acid (PLA) electrodes for electrochemical setups. Such electrodes require activation from their pristine state for improved conductivity, so far achieved by chemical treatment. Herein, a new simple physical thermal annealing method to activate graphene-based PLA electrodes is presented. The graphene/PLA electrodes are fabricated via FDM 3D printing using a commercial graphene-polymer composite conductive filament and subjected to thermal and chemical activation with a subsequent electrochemical pre-treatment. The thermally annealed electrodes exhibit faster electron transfer than the chemically activated or non-treated electrodes in the inner sphere redox probe ferro/ferricyanide. The thermally activated graphene/PLA electrodes are also successfully employed as a low-cost alternative to nitroaromatic explosive sensors. This chemical-free activation method is a facile, fast, and simple route to activate conductive carbon/PLA 3D prints, which increases the electric conductivity and preserves the fine details of the printed objects, making this activation method relevant to a broad range of applied fields utilizing conductive polymer composites.

Nanomotor tracking experiments at the edge of reproducibility.

The emerging field of self-propelling micro/nanorobots is teeming with a wide variety of novel micro/nanostructures, which are tested here for self-propulsion in a liquid environment. As the size of these microscopic movers diminishes into the fully nanosized region, the ballistic paths of an active micromotor become a random walk of colloidal particles. To test such colloidal samples for self-propulsion, the commonly adopted "golden rule" is to refer to the mean squared displacement (MSD) function of the measured particle tracks. The practical significance of the result strongly depends on the amount of collected particle data and the sampling rate of the particle track. Because micro/nanomotor preparation methods are mostly low-yield, the amount of used experimental data in published results is often on the edge of reproducibility. To address the situation, we perform MSD analysis on an experimental as well as simulated dataset. These data are used to explore the effects of MSD analysis on limited data and several situations where the lack of data can lead to insignificant results.

Micromotors as "Motherships": A Concept for the Transport, Delivery, and Enzymatic Release of Molecular Cargo via Nanoparticles.

Nano/micromotors based on biodegradable and biocompatible polymers represent a progressively developing group of self-propelled artificial devices capable of delivering biologically active compounds to target sites. The majority of these machines are micron sized, and biologically active compounds are simply attached to their surface. Micron-sized devices cannot enter cells, but they provide rapid velocity, which scales down with the size of the device; nanosized devices can enter cells, but their velocity is negligible. An advanced hierarchical design of the micro/nanodevices is an important tool in the development of functional biocompatible transport systems and their implementation in real in vivo applications. In this work, we demonstrate a "mothership" concept, whereby self-propelled microrobots transport smaller cargo-carrying nanorobots that are released by enzymatic degradation.

Visible-Light-Driven Single-Component BiVO4 Micromotors with the Autonomous Ability for Capturing Microorganisms.

Light-driven micro/nanomotors represent the next generation of automotive devices that can be easily actuated and controlled by using an external light source. As the field evolves, there is a need for developing more sophisticated micromachines that can fulfill diverse tasks in complex environments. Herein, we introduce single-component BiVO4 micromotors with well-defined micro/nanostructures that can swim both individually and as collectively assembled entities under visible-light irradiation. These devices can perform cargo loading and transport of passive particles as well as living microorganisms without any surface functionalization. Interestingly, after photoactivation, the BiVO4 micromotors exhibited an ability to seek and adhere to yeast cell walls, with the possibility to control their attachment/release by switching the light on/off, respectively. Taking advantage of the selective motor/fungal cells attachment, the fungicidal activity of BiVO4 micromotors under visible illumination was also demonstrated. The presented star-shaped BiVO4 micromotors, obtained by a hydrothermal synthesis, contribute to the potential large-scale fabrication of light-powered micromotors. Moreover, these multifunctional single-component micromachines with controlled self-propulsion, collective behavior, cargo transportation, and photocatalytic activity capabilities hold promising applications in sensing, biohybrids assembly, cargo delivery, and microbiological water pollution remediation.

A Metal-Doped Fungi-Based Biomaterial for Advanced Electrocatalysis.

Nature and its highly sophisticated biomaterials are an endless source of inspiration for engineers and scientists across a wide range of disciplines. During the last decade, concepts of bioinspired synthesis of hierarchically structured nano- and micromaterials have been attracting increasing attention. In this article, we have utilized the natural ability of fungi to absorb metal ions for a bioinspired synthesis of carbonaceous material doped by selected transition metals. As an all-around metal accumulator, Hebeloma mesophaeum was selected, and it was cultivated in the presence of three transition-metal ions: NiII , FeII , and MnII . The metal-doped carbonized biomaterial possessed enhanced catalytic activity toward hydrazine oxidation, oxygen reduction, and cumene hydroperoxide reduction. Thus, we have shown possible transformation of a waste product (fungi grown on a contaminated soil) into a value-added carbonaceous material with tailored catalytic properties. This bioinspired synthesis can outline an attractive route for the fabrication of catalysts for important industrial applications on a large scale.

3D Printed Graphene Electrodes' Electrochemical Activation.

Three-dimensional (3D) printing technologies are emerging as an important tool for the manufacturing of electrodes for various electrochemistry applications. It has been previously shown that metal 3D electrodes, modified with metal oxides, are excellent catalysts for various electrochemical energy and sensing applications. However, the metal 3D printing process, also known as selective laser melting, is extremely costly. One alternative to metal-based electrodes for the aforementioned electrochemical applications is graphene-based electrodes. Nowadays, the printing of polymer-/graphene-based electrodes can be carried out in a matter of minutes using cheap and readily available 3D printers. Unfortunately, these polymer/graphene electrodes exhibit poor electrochemical activity in their native state. Herein, we report on a simple activation method for graphene/polymer 3D printed electrodes by a combined solvent and electrochemical route. The activated electrodes exhibit a dramatic increase in electrochemical activity with respect to the [Fe(CN)6]4-/3- redox couple and the hydrogen evolution reaction. Such in situ activation can be applied on-demand, thus providing a platform for the further widespread utilization of 3D printed graphene/polymer electrodes for electrochemistry.

3D-Printed Graphene/Polylactic Acid Electrodes Promise High Sensitivity in Electroanalysis.

Additive manufacturing provides a unique tool for prototyping structures toward electrochemical sensing, due to its ability to produce highly versatile, tailored-shaped devices in a low-cost and fast way with minimized waste. Here we present 3D-printed graphene electrodes for electrochemical sensing. Ring- and disc-shaped electrodes were 3D-printed with a Fused Deposition Modeling printer and characterized using cyclic voltammetry and scanning electron microscopy. Different redox probes K3Fe(CN)6:K4Fe(CN)6, FeCl3, ascorbic acid, Ru(NH3)6Cl3, and ferrocene monocarboxylic acid) were used to assess the electrochemical performance of these devices. Finally, the electrochemical detection of picric acid and ascorbic acid was carried out as proof-of-concept analytes for sensing applications. Such customizable platforms represent promising alternatives to conventional electrodes for a wide range of sensing applications.

Biological safety and tissue distribution of (16-mercaptohexadecyl)trimethylammonium bromide-modified cationic gold nanorods.

The exceptionally high cellular uptake of gold nanorods (GNRs) bearing cationic surfactants makes them a promising tool for biomedical applications. Given the known specific toxic and stress effects of some preparations of cationic nanoparticles, the purpose of this study was to evaluate, in an in vitro and in vivo in mouse, the potential harmful effects of GNRs coated with (16-mercaptohexadecyl)trimethylammonium bromide (MTABGNRs). Interestingly, even after cellular accumulation of high amounts of MTABGNRs sufficient for induction of photothermal effect, no genotoxicity (even after longer-term accumulation), induction of autophagy, destabilization of lysosomes (dominant organelles of their cellular destination), alterations of actin cytoskeleton, or in cell migration could be detected in vitro. In vivo, after intravenous administration, the majority of GNRs accumulated in mouse spleen followed by lungs and liver. Microscopic examination of the blood and spleen showed that GNRs interacted with white blood cells (mononuclear and polymorphonuclear leukocytes) and thrombocytes, and were delivered to the spleen red pulp mainly as GNR-thrombocyte complexes. Importantly, no acute toxic effects of MTABGNRs administered as 10 or 50 µg of gold per mice, as well as no pathological changes after their high accumulation in the spleen were observed, indicating good tolerance of MTABGNRs by living systems.

Two-Step Mechanism of Cellular Uptake of Cationic Gold Nanoparticles Modified by (16-Mercaptohexadecyl)trimethylammonium Bromide.

Cationic colloidal gold nanorods (GNRs) have a great potential as a theranostic tool for diverse medical applications. GNRs' properties such as cellular internalization and stability are determined by physicochemical characteristics of their surface coating. GNRs modified by (16-mercaptohexadecyl)trimethylammonium bromide (MTAB), MTABGNRs, show excellent cellular uptake. Despite their promise for biomedicine, however, relatively little is known about the cellular pathways that facilitate the uptake of GNRs, their subcellular fate and intracellular persistence. Here we studied the mechanism of cellular internalization and long-term fate of GNRs coated with MTAB, for which the synthesis was optimized to give higher yield, in various human cell types including normal diploid versus cancerous, and dividing versus nondividing (senescent) cells. The process of MTABGNRs internalization into their final destination in lysosomes proceeds in two steps: (1) fast passive adhesion to cell membrane mediated by sulfated proteoglycans occurring within minutes and (2) slower active transmembrane and intracellular transport of individual nanorods via clathrin-mediated endocytosis and of aggregated nanorods via macropinocytosis. The expression of sulfated proteoglycans was the major factor determining the extent of uptake by the respective cell types. Upon uptake into proliferating cells, MTABGNRs were diluted equally and relatively rapidly into daughter cells; however, in nondividing/senescent cells the loss of MTABGNRs was gradual and very modest, attributable mainly to exocytosis. Exocytosed MTABGNRs can again be internalized. These findings broaden our knowledge about cellular uptake of gold nanorods, a crucial prerequisite for future successful engineering of nanoparticles for biomedical applications such as photothermal cancer therapy or elimination of senescent cells as part of the emerging rejuvenation approach.

In situ WetSTEM observation of gold nanorod self-assembly dynamics in a drying colloidal droplet.

Direct in situ visualization of nanoparticles in a liquid is an important challenge of modern electron microscopy. The increasing significance of bottom-up methods in nanotechnology requires a direct method to observe nanoparticle interactions in a liquid as the counterpart to the ex situ electron microscopy and indirect scattering and spectroscopy methods. Especially, the self-assembly of anisometric nanoparticles represents a difficult task, and the requirement to trace the route and orientation of an individual nanoparticle is of highest importance. In our approach we utilize scanning transmission electron microscopy under environmental conditions to visualize the mobility and self-assembly of cetyltrimethylammonium bromide (CTAB)-capped gold nanorods (AuNRs) in an aqueous colloidal solution. We directly observed the drying-mediated AuNR self-assembly in situ during rapid evaporation of a colloidal droplet at 4°C and pressure of about 900 Pa. Several types of final AuNR packing were documented including side-by-side oriented chains, tip-to-tip loosely arranged nanorods, and domains of vertically aligned AuNR arrays. The effect of local heating by electron beam is used to qualitatively asses the visco-elastic properties of the formed AuNR/CTAB/water membrane. Local heating induces the dehydration and contraction of a formed membrane indicated either by its rupture and/or by movement of the embedded AuNRs.

High-aspect-ratio and high-flatness Cu3(SiGe) nanoplatelets prepared by chemical vapor deposition.

Cu3(SiGe) nanoplatelets were synthesized by low-pressure chemical vapor deposition of a SiH3C2H5/Ge2(CH3)6 mixture on a Cu-substrate at 500 degrees C, total pressure of 110-115 Pa, and Ge/Si molar ratio of 22. The nanoplatelets with composition Cu76Si15Ge12 are formed by the 4'-phase, and they are flattened perpendicular to the [001] direction. Their lateral dimensions reach several tens of micrometers in size, but they are only about 50 nm thick. Their surface is extremely flat, with measured root mean square roughness R(q) below 0.2 nm. The nanoplatelets grow via the non-catalytic vapor-solid mechanism and surface growth. In addition, nanowires and nanorods of various Cu-Si-Ge alloys were also obtained depending on the experimental conditions. Morphology of the resulting Cu-Si-Ge nanoobjects is very sensitive to the experimental parameters. The formation of nanoplatelets is associated with increased amount of Ge in the alloy.