Publications

Enzymatic nanomotors harvest kinetic energy through the catalysis of chemical fuels. When a drop containing nanomotors is placed in a fuel-rich environment, they assemble into ordered groups and exhibit intriguing collective behaviour akin to the bioconvection of aerobic microorganismal suspensions. This collective behaviour presents numerous advantages compared to individual nanomotors, including expanded coverage and prolonged propulsion duration. However, the physical mechanisms underlying the collective motion have yet to be fully elucidated. Our study investigates the formation of enzymatic swarms using experimental analysis and computational modelling. We show that the directional movement of enzymatic nanomotor swarms is due to their solutal buoyancy. We investigate various factors that impact the movement of nanomotor swarms, such as particle concentration, fuel concentration, fuel viscosity, and vertical confinement. We examine the effects of these factors on swarm self-organization to gain a deeper understanding. In addition, the urease catalysis reaction produces ammonia and carbon dioxide, accelerating the directional movement of active swarms in urea compared with passive ones in the same conditions. The numerical analysis agrees with the experimental findings. Our findings are crucial for the potential biomedical applications of enzymatic nanomotor swarms, ranging from enhanced diffusion in bio-fluids and targeted delivery to cancer therapy. Enzymatic nanomotors exhibit collective behaviour in fuel-rich environments, forming swarms with enhanced propulsion and coverage. This study investigates the factors affecting swarm movement, revealing that solutal buoyancy drives their motion, with potential biomedical applications like targeted drug delivery.

JTD Keywords: Ammonia, Behavior, Carbon dioxide, Catalysis, Computer simulation, Kinetics, Motion, Nanostructures, Powered nanomotors, Propulsion, Urease, Viscosity

This study investigates the synthesis and optimization of nanobots (NBs) loaded with pDNA using the layer-by-layer (LBL) method and explores the impact of their collective motion on the transfection efficiency. NBs consist of biocompatible and biodegradable poly(lactic-co-glycolic acid) (PLGA) nanoparticles and are powered by the urease enzyme, enabling autonomous movement and collective swarming behavior. In vitro experiments were conducted to validate the delivery efficiency of fluorescently labeled NBs, using two-dimensional (2D) and three-dimensional (3D) cell models: murine urothelial carcinoma cell line (MB49) and spheroids from human urothelial bladder cancer cells (RT4). Swarms of pDNA-loaded NBs showed enhancements of 2.2- to 2.6-fold in delivery efficiency and 6.8- to 8.1-fold in material delivered compared to inhibited particles (inhibited enzyme) and the absence of fuel in a 2D cell culture. Additionally, efficient intracellular delivery of pDNA was demonstrated in both cell models by quantifying and visualizing the expression of eGFP. Swarms of NBs exhibited a >5-fold enhancement in transfection efficiency compared to the absence of fuel in a 2D culture, even surpassing the Lipofectamine 3000 commercial transfection agent (cationic lipid-mediated transfection). Swarms also demonstrated up to a 3.2-fold enhancement in the amount of material delivered in 3D spheroids compared to the absence of fuel. The successful transfection of 2D and 3D cell cultures using swarms of LBL PLGA NBs holds great potential for nucleic acid delivery in the context of bladder treatments.

JTD Keywords: Animals, Barrier, Cell line, tumor, Dna, Drug delivery, Drug-delivery, Enzyme catalysis, Gene delivery, Gene transfer techniques, Humans, Lactic acid, Mice, Nanobots, Nanoparticles, Pdna, Plasmids, Polyglycolic acid, Polylactic acid-polyglycolic acid copolymer, Swarming, Transfectio, Transfection, Urease, Urinary bladder neoplasms

Photocatalytic nanomotors have attracted a lot of attention because of their unique capacity to simultaneously convert light and chemical energy into mechanical motion with a fast photoresponse. Recent discoveries demonstrate that the integration of optical and magnetic components within a single nanomotor platform offers novel advantages for precise motion control and enhanced photocatalytic performance. Despite these advancements, the impact of magnetic fields on energy transfer dynamics in photocatalytic nanomotors remains unexplored. Here, we introduce dual-responsive rod-like nanomotors, made of a TiO2/NiFe heterojunction, able to (i) self-propel upon irradiation, (ii) align with the direction of an external magnetic field, and (iii) exhibit enhanced photocatalytic performance. Consequently, when combining light irradiation with a homogeneous magnetic field, these nanomotors exhibit increased velocities attributed to their improved photoactivity. As a proof-of-concept, we investigated the ability of these nanomotors to generate phenol, a valuable chemical feedstock, from benzene under combined optical and magnetic fields. Remarkably, the application of an external magnetic field led to a 100% increase in the photocatalytic phenol generation in comparison with light activation alone. By using various state-of-the-art techniques such as photoelectrochemistry, electrochemical impedance spectroscopy, photoluminescence, and electron paramagnetic resonance, we characterized the charge transfer between the semiconductor and the alloy component, revealing that the magnetic field significantly improved charge pair separation and enhanced hydroxyl radical generation. Consequently, our work provides valuable insights into the role of magnetic fields in the mechanisms of light-driven photocatalytic nanomotors for designing more effective light-driven nanodevices for selective oxidations.

JTD Keywords: Charge transfer, Dual-responsive nanomotors, Magnetic properties, Photoactive nanomotors, Photocatalysis, Selective oxidations

Here, we report DNA-based synthetic nanostructures decorated with enzymes (hereafter referred to as DNA-enzyme swimmers) that self-propel by converting the enzymatic substrate to the product in solution. The DNA-enzyme swimmers are obtained from tubular DNA structures that self-assemble spontaneously by the hybridization of DNA tiles. We functionalize these DNA structures with two different enzymes, urease and catalase, and show that they exhibit concentration-dependent movement and enhanced diffusion upon addition of the enzymatic substrate (i.e., urea and H2O2). To demonstrate the programmability of such DNA-based swimmers, we also engineer DNA strands that displace the enzyme from the DNA scaffold, thus acting as molecular brakes on the DNA swimmers. These results serve as a first proof of principle for the development of synthetic DNA-based enzyme-powered swimmers that can self-propel in fluids.

JTD Keywords: Biocatalysis, Catalase, Design, Dna, Hydrogen peroxide, Motor, Nanostructures, Shapes, Urease

Targeted drug delivery depends on the ability of nanocarriers to reach the target site, which requires the penetration of different biological barriers. Penetration is usually low and slow because of passive diffusion and steric hindrance. Nanomotors (NMs) have been suggested as the next generation of nanocarriers in drug delivery due to their autonomous motion and associated mixing hydrodynamics, especially when acting collectively as a swarm. Here, we explore the concept of enzyme-powered NMs designed as such that they can exert disruptive mechanical forces upon laser irradiation. The urease-powered motion and swarm behavior improve translational movement compared to passive diffusion of state-of-the-art nanocarriers, while optically triggered vapor nanobubbles can destroy biological barriers and reduce steric hindrance. We show that these motors, named Swarm 1, collectively displace through a microchannel blocked with type 1 collagen protein fibers (barrier model), accumulate onto the fibers, and disrupt them completely upon laser irradiation. We evaluate the disruption of the microenvironment induced by these NMs (Swarm 1) by quantifying the efficiency by which a second type of fluorescent NMs (Swarm 2) can move through the cleared microchannel and be taken up by HeLa cells at the other side of the channel. Experiments showed that the delivery efficiency of Swarm 2 NMs in a clean path was increased 12-fold in the presence of urea as fuel compared to when no fuel was added. When the path was blocked with the collagen fibers, delivery efficiency dropped considerably and only depicted a 10-fold enhancement after pretreatment of the collagen-filled channel with Swarm 1 NMs and laser irradiation. The synergistic effect of active motion (chemically propelled) and mechanical disruption (light-triggered nanobubbles) of a biological barrier represents a clear advantage for the improvement of therapies which currently fail due to inadequate passage of drug delivery carriers through biological barriers.

JTD Keywords: drug delivery, enzyme catalysis, nanoparticles, swarming, vapor nanobubbles, Drug carriers, Drug delivery, Drug delivery systems, Enzyme catalysis, Hela cells, Humans, Nanomotors, Nanoparticles, Swarming, Vapor nanobubbles

Magnetic resonance techniques are successfully utilized in a broad range of scientific disciplines and in various practical applications, with medical magnetic resonance imaging being the most widely known example. Currently, both fundamental and applied magnetic resonance are enjoying a major boost owing to the rapidly developing field of spin hyperpolarization. Hyperpolarization techniques are able to enhance signal intensities in magnetic resonance by several orders of magnitude, and thus to largely overcome its major disadvantage of relatively low sensitivity. This provides new impetus for existing applications of magnetic resonance and opens the gates to exciting new possibilities. In this review, we provide a unified picture of the many methods and techniques that fall under the umbrella term "hyperpolarization" but are currently seldom perceived as integral parts of the same field. Specifically, before delving into the individual techniques, we provide a detailed analysis of the underlying principles of spin hyperpolarization. We attempt to uncover and classify the origins of hyperpolarization, to establish its sources and the specific mechanisms that enable the flow of polarization from a source to the target spins. We then give a more detailed analysis of individual hyperpolarization techniques: the mechanisms by which they work, fundamental and technical requirements, characteristic applications, unresolved issues, and possible future directions. We are seeing a continuous growth of activity in the field of spin hyperpolarization, and we expect the field to flourish as new and improved hyperpolarization techniques are implemented. Some key areas for development are in prolonging polarization lifetimes, making hyperpolarization techniques more generally applicable to chemical/biological systems, reducing the technical and equipment requirements, and creating more efficient excitation and detection schemes. We hope this review will facilitate the sharing of knowledge between subfields within the broad topic of hyperpolarization, to help overcome existing challenges in magnetic resonance and enable novel applications.

JTD Keywords: electron-paramagnetic-resonance, high-resolution nmr, hydrogen-induced polarization, level anti-crossings, long-lived states, parahydrogen-induced polarization, photosynthetic reaction-center, reversible exchange catalysis, solid-state nmr, Dynamic-nuclear-polarization

Although an increasing number of micro/nanomotors have been designed for environmental remediation in the past decade, the construction of contaminants-fueled nanomotors for synergistically degrading multiple pollutants simultaneously remains a challenge. Herein, laccase-powered Fe3O4@silica nanomotors are fabricated, assisted with lipase enzyme for the enhanced degradation of multiple contaminants using the contaminants themselves as fuels. Notably, we demonstrate that representative industrial phenols and polycyclic aromatic pollutants possess the ability of triggering the enhanced Brownian motion of laccase nanomotors (De of 1.16 mu m(2)/s in 220 mu M biphenol A (BPA), 1.40 mu m(2)/s in 375 mu M Congo red (CR)). Additionally, the k(cat) value of lipase-assisted laccase-powered nanomotors increased over 1.4 times, enhancing their Brownian motion, while leading to the efficient degradation of multiple contaminants such as BPA, CR, and triacetin droplets within 40 min, simultaneously. Ultimately, the lipase-assisted laccase nanomotors exhibit great advantages over free laccase, free lipase, lipase nanomotors, or laccase nanomotors in K-m, k(cat), catalytic stability, recycling property, and the degradation efficiency of contaminants. Therefore, our work further broadens the library of enzyme-powered nanomotors and provides deep insights in synergistical enzymatic catalysis, thus paving avenues for environmental remediation based on enzyme-powered micro/nanomotors. (C) 2022 Elsevier Ltd. All rights reserved.

JTD Keywords: core, dye, environmental remediation, enzyme catalysis, hybrid, light, microspheres, motors, pollutants removal, propulsion, removal, self-propulsion, shell, Core, Dye, Environmental remediation, Enzyme catalysis, Hybrid, Light, Micro/nanomotors, Micromotors, Microspheres, Motors, Pollutants removal, Propulsion, Removal, Self-propulsion, Shell

The design of catalysts with controlled selectivity at will, also known as catalytic plasticity, is a very attractive approach for the recycling of carbon dioxide (CO2). In this work, we study how catalytically active hydroxyapatite (HAp) and brushite (Bru) interact synergistically, allowing the production of formic acid or acetic acid depending on the HAp/Bru ratio in the catalyst. Raman, wide angle X-ray scattering, X-ray photoelectron spectroscopy, scanning electron microscopy and electrochemical impedance spectroscopy studies, combined with an exhaustive revision of the crystalline structure of the catalyst at the atomic level, allowed to discern how the Bru phase can be generated and stabilized at high temperatures. Results clearly indicate that the presence of OH– groups to maintain the crystalline structural integrity in conjunction with Ca2+ ions less bonded to the lattice fixate carbon into C1, C2 and C3 molecules from CO2 and allow the evolution from formic to acetic acid and acetone. In this way, the plasticity of the HAp-Bru system is demonstrated, representing a promising green alternative to the conventional metal-based electrocatalysts used for CO2 fixation. Thus, the fact that no electric voltage is necessary for the CO2 reduction has a very favorable impact in the final energetic net balance of the carbon fixation reaction. © 2021

JTD Keywords:

ethanol production & nbsp, brushite, co2 reduction, conversion, electrocatalytic reduction, electrode, formate, heterogeneous catalysis & nbsp, hydrogen evolution, insights, monetite, polarized hydroxyapatite,

Enzyme-powered micro- and nanomotors make use of biocatalysis to self-propel in aqueous media and hold immense promise for active and targeted drug delivery. Most (if not all) of these micro- and nanomotors described to date are fabricated using a commercially available enzyme, despite claims that some commercial preparations may not have a sufficiently high degree of purity for downstream applications. In this study, the purity of a commercial urease, an enzyme frequently used to power the motion of micro- and nanomotors, was evaluated and found to be impure. After separating the hexameric urease from the protein impurities by size-exclusion chromatography, the hexameric urease was subsequently characterized and used to functionalize hollow silica microcapsules. Micromotors loaded with purified urease were found to be 2.5 times more motile than the same micromotors loaded with unpurified urease, reaching average speeds of 5.5 ?m/s. After comparing a number of parameters, such as enzyme distribution, protein loading, and motor reusability, between micromotors functionalized with purified vs unpurified urease, it was concluded that protein purification was essential for optimal performance of the enzyme-powered micromotor.

JTD Keywords: canavalin, catalysis, delivery, dls, enhanced diffusion, enzyme, lipase immobilization, micromotors, self-propulsion, super-resolution microscopy, urease, Mesoporous silica nanoparticles, Micromotors, Super-resolution microscopy

JTD Keywords: amino-acids, catalysis, dopant-free hydroxyapatite, electrical properties, electrophotosynthesis, nitrogen, thermally-stimulated polarization, Advanced materials, Biocompatibility, Biomedical applications, Brushite, Doped hydroxyapatites, Electric voltage, Electrical characterization, Electrochemical impedance spectroscopy, Equivalent circuits, Future perspectives, Highest temperature, Hydroxyapatite, Interfaces (materials), Material interfaces, Medical applications, Polarization, Polarization conditions, Surface-charges, Technological applications

A new methodology for the pH-triggered degradation of polymers or for the release of drugs under visible light irradiation based on the cyclization of ortho-hydroxy-cinnamates (oHC) to coumarins is described. The key oHC structural motif can be readily incorporated into the rational design of novel photocleavable polymers via click chemistry. This main-chain moiety undergoes a fast photocleavage when irradiated with 455 nm light provided that a suitable base is added. A series of polyethylene glycol-alt-ortho-hydroxy cinnamate (polyethylene glycol (PEG)(n)-alt-oHC)-based polymers are synthesized and the time-dependent visible-light initiated cleavage of the photoactive monomer and polymer is investigated in solution by a variety of spectroscopic and chromatographic techniques. The photo-degradation behavior of the water-soluble poly(PEG(2000)-alt-oHC) is investigated within a broad pH range (pH = 2.1-11.8), demonstrating fast degradation at pH 11.8, while the stability of the polymer is greatly enhanced at pH 2.1. Moreover, the neat polymer shows long-term stability under daylight conditions, thus allowing its storage without special precautions. In addition, two water-soluble PEG-based drug-carrier molecules (mPEG(2000)-oHC-benzhydrol/phenol) are synthesized and used for drug delivery studies, monitoring the process by UV-vis spectroscopy in an ON/OFF intermittent manner.

JTD Keywords: coumarins, drug delivery, e/z-double bond isomerization, o-hydroxy cinnamates, polymer degradation, Aliphatic compounds, Antioxidant activity, Antitumor, Chromatographic techniques, Chromatography, Cis/trans isomerization, Controlled drug delivery, Coumarin derivatives, Coumarins, Drug delivery, Drug delivery system, E/z-double bond isomerization, Films, Hydrogels, Image enhancement, Light, Long term stability, O-hydroxy cinnamates, Particles, Photoactive monomers, Photodegradation, Polyethylene glycols, Polyethylenes, Polymer degradation, Responsive polymers, Salts, Structural motifs, Synthesis (chemical), Targeted drug delivery, Visible light photocatalysis, Visible-light irradiation

The enhanced catalytic activity of permanently polarized hydroxyapatite, which is achieved using a thermally stimulated polarization process, largely depends on both the experimental conditions used to prepare crystalline hydroxyapatite from its calcium and phosphate precursors and the polarization process parameters. A mineral similar to brushite, which is an apatitic phase that can evolve to hydroxyapatite, is found at the surface of highly crystalline hydroxyapatite. It appears after chemical precipitation and hydrothermal treatment performed at 150 degrees C for 24 h followed by a sinterization at 1000 degrees C and a polarization treatment by applying a voltage of 500 Vat high temperature. Both the high crystallinity and the presence of brushite-like phase on the electrophotocatalyst affect the nitrogen and carbon fixation under mild reaction conditions (95 degrees C and 6 bar) and the synthesis of glycine and alanine from a simple gas mixture containing N-2, CO2, CH4 and H2O. Thus, the Gly/Ala ratio can be customized by controlling the presence of brushite on the surface of the catalyst, enabling to develop new strategies to regulate the production of amino acids by nitrogen and carbon fixation. (C) 2021 Elsevier Inc. All rights reserved.

JTD Keywords: Amino acids, Brushite, Carbon, Carbon dioxide fixation, Catalyst activity, Catalytic apatites, Chemical precipitation, Crystalline hydroxyapatite, Crystallinity, Decomposition, Enhanced catalytic activity, Experimental conditions, Heterogeneous catalysis, High crystallinity, Hydrothermal synthesis, Hydrothermal treatments, Hydroxyapatite, Lactic-acid, Mild reaction conditions, Molecular nitrogen fixation, Nitrogen, Nitrogen fixation, Phosphate, Polarization, Precipitation (chemical), Process parameters, Thermally stimulated polarization

The low efficacy of current conventional treatments for bacterial infections increases mortality rates worldwide. To alleviate this global health problem, we propose drug-free enzyme-based nanomotors for the treatment of bacterial urinary-tract infections. We develop nanomotors consisting of mesoporous silica nanoparticles (MSNPs) that were functionalized with either urease (U-MSNPs), lysozyme (L-MSNPs), or urease and lysozyme (M-MSNPs), and use them against nonpathogenic planktonic Escherichia coli. U-MSNPs exhibited the highest bactericidal activity due to biocatalysis of urea into NaHCO3 and NH3, which also propels U-MSNPs. In addition, U-MSNPs in concentrations above 200 μg/mL were capable of successfully reducing 60% of the biofilm biomass of a uropathogenic E. coli strain. This study thus provides a proof-of-concept, demonstrating that enzyme-based nanomotors are capable of fighting infectious diseases. This approach could potentially be extended to other kinds of diseases by selecting appropriate biomolecules.

JTD Keywords: biofilms, carbonate, e. coli, enzymatic nanomotors, infections, lysozyme, micromotors, nanomachines, proteins, self-propulsion, Anti-bacterial agents, Biocatalysis, Biofilms, Canavalia, Drug carriers, E. coli, Eliminate escherichia-coli, Enzymatic nanomotors, Escherichia coli, Escherichia coli infections, Humans, Infections, Muramidase, Nanomachines, Nanoparticles, Self-propulsion, Silicon dioxide, Urease, Urinary tract infections

The electrophotocatalytic synthesis of Glycine and Alanine from a simple gas mixture containing N2, CO2, CH4 and H2O under mild reaction conditions (95 °C and 6 bar) was recently developed using a catalyst formed by permanently polarized hydroxyapatite, which is achieved using a thermally stimulated polarization process, coated with two layers of aminotris(methylenephosphonic acid) (ATMP) separated by an intermediate layer of zirconyl chloride (ZC). This work reports the optimization of the ATMP- and ZC-coating content by examining the influence of their concentration of each component in each layer on the structural and electrochemical properties of the catalyst. After exhaustive analyses, such properties have been related with the efficiency of the catalysts prepared using different ATMP- and ZC-concentrations to yield Gly and Ala amino acids by fixing nitrogen from N2 and carbon from CO2 and CH4. Results show that, although the concentrations of ATMP and ZC in the first and the intermediate layers are important, the third layer plays a predominant role as is responsible of the apparition of supramolecular structures on the surface and the capacitive behavior of the coating

JTD Keywords: Carbon dioxide fixation, Electrocatalyst, Heterogeneous catalysis, Phosphonic acid, Photocatalyst, Polarized hydroxyapatite, Surface chemistry, Zirconyl chloride

The introduction of stimuli-responsive cargo release capabilities on self-propelled micro- and nanomotors holds enormous potential in a number of applications in the biomedical field. Herein, we report the preparation of mesoporous silica nanoparticles gated with pH-responsive supramolecular nanovalves and equipped with urease enzymes which act as chemical engines to power the nanomotors. The nanoparticles are loaded with different cargo molecules ([Ru(bpy)3]Cl2 (bpy = 2,2′-bipyridine) or doxorubicin), grafted with benzimidazole groups on the outer surface, and capped by the formation of inclusion complexes between benzimidazole and cyclodextrin-modified urease. The nanomotor exhibits enhanced Brownian motion in the presence of urea. Moreover, no cargo is released at neutral pH, even in the presence of the biofuel urea, due to the blockage of the pores by the bulky benzimidazole:cyclodextrin-urease caps. Cargo delivery is only triggered on-command at acidic pH due to the protonation of benzimidazole groups, the dethreading of the supramolecular nanovalves, and the subsequent uncapping of the nanoparticles. Studies with HeLa cells indicate that the presence of biofuel urea enhances nanoparticle internalization and both [Ru(bpy)3]Cl2 or doxorubicin intracellular release due to the acidity of lysosomal compartments. Gated enzyme-powered nanomotors shown here display some of the requirements for ideal drug delivery carriers such as the capacity to self-propel and the ability to “sense” the environment and deliver the payload on demand in response to predefined stimuli.

JTD Keywords: Controlled release, Drug delivery, Enzymatic catalysis, Gatekeepers, Nanocarriers, Nanomotors, Stimuli-responsive nanomaterials

Cancer is one of the main causes of death around the world, lacking efficient clinical treatments that generally present severe side effects. In recent years, various nanosystems have been explored to specifically target tumor tissues, enhancing the efficacy of cancer treatment and minimizing the side effects. In particular, bladder cancer is the ninth most common cancer worldwide and presents a high survival rate but serious recurrence levels, demanding an improvement in the existent therapies. Here, we present urease-powered nanomotors based on mesoporous silica nanoparticles that contain both polyethylene glycol and anti-FGFR3 antibody on their outer surface to target bladder cancer cells in the form of 3D spheroids. The autonomous motion is promoted by urea, which acts as fuel and is inherently present at high concentrations in the bladder. Antibody-modified nanomotors were able to swim in both simulated and real urine, showing a substrate-dependent enhanced diffusion. The internalization efficiency of the antibody-modified nanomotors into the spheroids in the presence of urea was significantly higher compared with antibody-modified passive particles or bare nanomotors. Furthermore, targeted nanomotors resulted in a higher suppression of spheroid proliferation compared with bare nanomotors, which could arise from the local ammonia production and the therapeutic effect of anti-FGFR3. These results hold significant potential for the development of improved targeted cancer therapy and diagnostics using biocompatible nanomotors.

JTD Keywords: 3D cell culture, Bladder cancer, Enzymatic catalysis, Nanomachines, Nanomotors, Self-propulsion, Targeting

Bio-catalytic micro- and nanomotors self-propel by the enzymatic conversion of substrates into products. Despite the advances in the field, the fundamental aspects underlying enzyme-powered self-propulsion have rarely been studied. In this work, we select four enzymes (urease, acetylcholinesterase, glucose oxidase, and aldolase) to be attached on silica microcapsules and study how their turnover number and conformational dynamics affect the self-propulsion, combining both an experimental and molecular dynamics simulations approach. Urease and acetylcholinesterase, the enzymes with higher catalytic rates, are the only enzymes capable of producing active motion. Molecular dynamics simulations reveal that urease and acetylcholinesterase display the highest degree of flexibility near the active site, which could play a role on the catalytic process. We experimentally assess this hypothesis for urease micromotors through competitive inhibition (acetohydroxamic acid) and increasing enzyme rigidity (β-mercaptoethanol). We conclude that the conformational changes are a precondition of urease catalysis, which is essential to generate self-propulsion.

JTD Keywords: Biocatalysis, Immobilized enzymes, Molecular machines and motors

The use of enzyme catalysis to power micro- and nanomotors exploiting biocompatible fuels has opened new ventures for biomedical applications such as the active transport and delivery of specific drugs to the site of interest. Here, urease-powered nanomotors (nanobots) for doxorubicin (Dox) anticancer drug loading, release, and efficient delivery to cells are presented. These mesoporous silica-based core-shell nanobots are able to self-propel in ionic media, as confirmed by optical tracking and dynamic light scattering analysis. A four-fold increase in drug release is achieved by nanobots after 6 h compared to their passive counterparts. Furthermore, the use of Dox-loaded nanobots presents an enhanced anticancer efficiency toward HeLa cells, which arises from a synergistic effect of the enhanced drug release and the ammonia produced at high concentrations of urea substrate. A higher content of Dox inside HeLa cells is detected after 1, 4, 6, and 24 h incubation with active nanobots compared to passive Dox-loaded nanoparticles. The improvement in drug delivery efficiency achieved by enzyme-powered nanobots may hold potential toward their use in future biomedical applications such as the substrate-triggered release of drugs in target locations.

JTD Keywords: Drug delivery, Enzymatic catalysis, Nanobots, Nanomachines, Nanomotors

Enzyme triggered bio-catalytic reactions convert chemical energy into mechanical force to power micro/nano-machines. Though there have been reports about enzymes powered micro/nano-motors, enzymatic Janus nano-motor smaller than 100 nm has not been reported yet. Here, we prepared an enzyme powered Janus nano-motor by half-capping a thin layer of silicon dioxide (4 nm SiO2) onto a mesoporous silica nanoparticle (MSNP) of 90 nm, enabling asymmetry to the nano-architecture. The nano-motors are chemically powered by the decomposition of H2O2 triggered by the enzyme catalase located at one face of the nanoparticles. The self-propulsion is characterized by dynamic light scattering (DLS) and optical microscopy. The apparent diffusion coefficient was enhanced by 150% compared to their Brownian motion at low H2O2 concentration (i.e. below 3 wt%). Mesoporous nano-motors might serve as active drug delivery nano-systems in future biomedical applications such as intracellular drug delivery.

JTD Keywords: Enzyme catalysis, Janus particles, Mesoporous silica, Nano-motors, Nanomachine, Self-propulsion

It is often thought that the ability to control reaction rates with an applied electrical potential gradient is unique to redox systems. However, recent theoretical studies suggest that oriented electric fields could affect the outcomes of a range of chemical reactions, regardless of whether a redox system is involved1, 2, 3, 4. This possibility arises because many formally covalent species can be stabilized via minor charge-separated resonance contributors. When an applied electric field is aligned in such a way as to electrostatically stabilize one of these minor forms, the degree of resonance increases, resulting in the overall stabilization of the molecule or transition state. This means that it should be possible to manipulate the kinetics and thermodynamics of non-redox processes using an external electric field, as long as the orientation of the approaching reactants with respect to the field stimulus can be controlled. Here, we provide experimental evidence that the formation of carbon–carbon bonds is accelerated by an electric field. We have designed a surface model system to probe the Diels–Alder reaction, and coupled it with a scanning tunnelling microscopy break-junction approach5, 6, 7. This technique, performed at the single-molecule level, is perfectly suited to deliver an electric-field stimulus across approaching reactants. We find a fivefold increase in the frequency of formation of single-molecule junctions, resulting from the reaction that occurs when the electric field is present and aligned so as to favour electron flow from the dienophile to the diene. Our results are qualitatively consistent with those predicted by quantum-chemical calculations in a theoretical model of this system, and herald a new approach to chemical catalysis.

JTD Keywords: Electrocatalysis, Scanning probe microscopy

Self-powered micromachines are promising tools for future environmental remediation technology. Waste-water treatment and water reuse is an essential part of environmental sustainability. Herein, we present reusable Fe/Pt multi-functional active microcleaners that are capable of degrading organic pollutants (malachite green and 4-nitrophenol) by generated hydroxyl radicals via a Fenton-like reaction. Various different properties of microcleaners, such as the effect of their size, short-term storage, long-term storage, reusability, continuous swimming capability, surface composition, and mechanical properties, are studied. It is found that these microcleaners can continuously swim for more than 24 hours and can be stored more than 5 weeks during multiple cleaning cycles. The produced microcleaners can also be reused, which reduces the cost of the process. During the reuse cycles the outer iron surface of the Fe/Pt microcleaners generates the in-situ, heterogeneous Fenton catalyst and releases a low concentration of iron into the treated water, while the mechanical properties also appear to be improved due to both its surface composition and structural changes. The microcleaners are characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), nanoindentation, and finite-element modeling (FEM).

JTD Keywords: Catalysts, Heterogeneous catalysis, Microcleaners, Micromotors, Nanorobots, Wastewater treatment

Chemically powered micro- and nanomotors are small devices that are self-propelled by catalytic reactions in fluids. Taking inspiration from biomotors, scientists are aiming to find the best architecture for self-propulsion, understand the mechanisms of motion, and develop accurate control over the motion. Remotely guided nanomotors can transport cargo to desired targets, drill into biomaterials, sense their environment, mix or pump fluids, and clean polluted water. This Review summarizes the major advances in the growing field of catalytic nanomotors, which started ten years ago.

JTD Keywords: Catalysis, Micromotors, Nanomotors, Robots, Self-propulsion