Microscale Motion and Light

Bio-catalytic micro- and nanomotors self-propel by the enzymatic conversion of substrates into products.1 Enzymes offer a combination of biocompatibility, bioavailability and versatility, making it a promising tool for certain biomedical applications.2 Despite the rapid advances in the field, a deeper understanding on the fundamental aspects that rule enzyme-powered self-propulsion is still required.3,4 In the present work, we selected four different 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 (MD) simulations approach. Urease and acetylcholinesterase, the enzymes with higher catalytic rates, were the only enzymes capable of producing active motion. MD simulations revealed that the four different enzymes displayed different flexibility near the active site and that conformational changes of urease and acetylcholinesterase displayed the highest degree of flexibility in the vicinity of the catalytic site, possibly playing a key role to facilitate substrate binding and product release. To better understand the relationship between conformational changes, catalysis and self-propulsion, we experimentally assess this hypothesis for the particular case of urease micromotors through competitive inhibition (acetohydroxamic acid) and increasing enzyme rigidity (β-mercaptoethanol). We conclude that the conformational changes are a precondition for urease catalysis, and that the rate of catalysis is essential and directly related to active motion. This study provides insight on the complex entanglement of conformational dynamics, catalysis and active motion, and contributes to the intelligent design of enzyme-based micromotors.

In the last decades microfabrication techniques have opened up new ways to study dynamics in artificial systems having complex and controllable shapes. In this line of research, the design and fabrication of efficient and self-powered micro-robots has been a very active research topic. Motile micro-organisms like E. coli may provide an optimal solution to generate propulsion in artificial microsystems. Microstructures can be transported when released on a layer of swarming bacteria, suspended in a bacterial bath or covered by surface adhering bacteria. Although it is possible to obtain a net movement in the mentioned cases, the displacement is stochastic and self-propulsion characteristics are hard to reproduce. In the present work we investigate possible design strategies for bio-hybrid micro shuttles having a defined number of propelling units that self-assemble onto precisely defined locations. The final design aims at minimizing friction and adhesion with the substrate while optimizing propulsion speed and self-assembly efficiency.

Colloidal motors that convert diverse energy sources into autonomous motion has drawn significant attention in the last two decades due to their usefulness in fundamental research and practical applications. Among the various types of colloidal motors, those driven by light have become a crucial branch of this research field due to its remote controllability and good tunability. As typically reported in the literature, light-driven colloidal motors move continuously when illuminated, but stop immediately once the light is removed. This is in agreement with low Reynolds hydrodynamics, where removing the propulsive force leads to an almost immediate stop of particle motion. Intriguingly and surprisingly, we found in a previous study that a pulsating Ag-PMMA Janus micromotors pulsed forward quite strongly for one last time when the light was turned off, but our understanding was very crude. In this poster presentation, we present a systematic investigation of the surprising behavior, termed “dark pulse”. In particular, we show that the amplitude and lag time of this dark pulse can be modulated by varying experimental parameters. In addition, pulsating motors showed three types of modes of motion when the light was switched on/off at different frequencies. Moreover, switching light can also regulate the collective behavior of oscillatory motors, generating collective pulsation and wave of activities. Studies of dark pulses might help us better understand the oscillatory dynamics of pulsating Janus motors, and the non-linearity mechanisms behind all the rich behaviors.

To any energy flow there is an associated flow of momentum, so that recoil forces arise every time an object absorbs or deflects incoming energy. This same principle governs the operation of macroscopic turbines as well as that of microscopic turbines that use light as the working fluid. However, a controlled and precise redistribution of optical energy is not easy to achieve at the micron scale resulting in a low efficiency of power to torque conversion. We use direct laser writing to fabricate 3D light guiding structures, shaped as a garden sprinkler, that can precisely reroute input optical power into multiple output channels. The shape parameters are derived from a detailed theoretical analysis of losses in curved microfibers. These optical reaction micro-turbines can maximally exploit light’s momentum to generate a strong, uniform and controllable torque.

Photocatalytic micro swimmers have many advantages. They are activated by light, which is a renewable, non-invasive energy source that can be applied remotely. It triggers the photocatalytic degradation of a certain fuel, which propels the micro swimmers by self-electrophoretic and/or diffusiophoretic mechanisms. To further exploit the potential applications of photocatalytic micro swimmers into more sensitive, biological setups, harmless fuels like pure H2O need to replace hydrogen peroxide, in combination with non-toxic photocatalytic materials. Bismuth vanadate is a very promising material to fulfil these requirements. With its narrow bandgap, it shows the potential to split pure water into hydrogen and oxygen (without depending on UV light). Additionally, it is completely nontoxic. Until now, no BiVO$_4$ micro swimmer has been proposed, but many differently shaped microstructures have been developed and compared concerning their photocatalytic performance. Especially micro- and nanostructured materials show great potential due to their high surface area and low electron-hole recombination rate. In this work, we present BiVO$_4$ microstructures with strong photocatalytic activity that show active propulsion under visible light and have therefore a great potential to become the powerful next generation of photocatalytic microswimmers.

Currently, different types of potential micro- or nanoswimmers such as magnetic microcarriers, catalytic microjets or helical swimmers are under investigation for cargo transport on the microscale [1]. Rather new types of self-propelling particles are the so-called self-thermophoretic Janus-particle swimmers, constituted of a segment that converts light into heat, and another segment that is either repelled from the heated zone or attracted towards it, leading to a laser-induced, directed movement of the swimmer. Several approaches were pursued for the construction of such hybrid systems. Besides silica [2] or polystyrene [3] beads that were partially capped with a thin gold film, also the combination of Janus particles and DNA as a direction stabilizer were investigated in this context [4]. The combination of a gold nanoparticle as the heating element and a DNA origami as the thermophoretic active part forming a self-thermophoretic swimmer was first reported by our group [4, 5]. Here, we use a circular DNA origami object not only as the thermophoretic active element, but also as a coupling element between different parts of the swimmer [6]. We present the design optimization of this DNA origami ring construct, its simulation by molecular dynamics studies as well as its synthesis and structural characterization. We achieve a specific and tight binding of one gold nanoparticle to one open side of the DNA origami ring due to multiple connection sites between both components, and thus, a nearly half-covered gold nanoparticle surface. Since DNA origami structures delineate “molecular breadboards” that can be decorated with different functionalities, an equally sized polystyrene bead or other cargo can be coupled to the other side of the DNA origami ring. The resulting sphere-dimer swimmer can then be guided by applying laser pulses to heat the gold nanoparticle every time, the aimed orientation of the hybrid is reached [3]. Due to the proximity of the thermophoretic active DNA origami ring to the heated zone, a high impact on the particle acceleration during a heating event can be achieved. In summary, we demonstrate that artificial self-propelled nanoswimmers can be assembled from a gold nanoparticle and a DNA origami ring, which can function as thermophoretic active component as well as cargo-coupling element. [1] S. Martel Biomicrofluidics 2016 10 021301. [2] H.-R. Jiang, N. Yoshinaga, M. Sano Phys. Rev. Lett. 2010 105 268302. [3] A. P. Bregulla, H. Yang, F. Cichos ACS Nano 2014 8 6542 [4] R. Schachoff, M. Selmke, A. Bregulla, F. Cichos, D. Rings, D. Chakraborty, K. Kroy, K. Günther, A. Henning-Knechtel, E. Sperling, M. Mertig diffusion-fundamentals.org 2015 23 1. [5] A. Herms, K. Günther, E. Sperling, A. Heerwig, A. Kick, F. Cichos, M. Mertig Phys. Status Solidi A 2017 214 1600957. [6] A. Heerwig, M. Schubel, C. Schirmer, A, Herms, F. Cichos, M. Mertig Phys. Status Solidi A 2019 published online, doi: 10.1002/pssa.201800775.

Ana C. Hortelão,1 Rafael Carrascosa,1 Nerea Murillo-Cremaes,1 Tania Patiño,2 Samuel Sánchez1,3 1 Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST), Baldiri i Reixac 10-12, 08028 Barcelona Spain 2 Department of Chemistry, University of Rome, Tor Vergata, Via della Ricerca Scientifica 1, Rome 00133, Italy 3 Institució Catalana de Recerca i Estudis Avancats (ICREA), Passeig Lluís Companys 23, 08010 Barcelona, Spain Biocatalytic micro- and nanomotors are structures capable of self-propulsion in fluids, due to the enzymatic conversion of substrates into products. 1,2 These structures have been considered of interest for biomedical applications, such as the active transport and delivery of cargoes to specific sites of interest, as well as to aid cell targeting and internalization phenomena. Here, we present fuel-dependent doxorubicin release and efficient delivery to cancer cells by urease powered nanomotors based on mesoporous silica nanoparticles,3 as well as their potential to target bladder cancer cells in the form of 3D spheroids by anchoring an antibody on their surface. 4 We observed that these nanomotors are able to propel in physiologically relevant fluids, such as PBS. Furthermore, we found a four-fold increase in doxorubicin release by nanomotors after 6 hours exposure to urea, compared to nanomotors without urea in the medium. Moreover, active drug-loaded nanomotors present improved anticancer efficiency toward HeLa cells, which arises from a synergistic effect between enhanced doxorubicin release and generation of ammonia during biocatalysis. We found that in the presence of urea, a higher content of doxorubicin is uptaken by cells after 1, 4, 6- and 24-hour incubations with active nanomotors, compared to passive carriers. In addition, we anchored anti-FGFR3 antibody to the surface of urease-powered nanomotors to target 3D bladder cancer spheroids. These nanomotors are able to self-propel in both simulated and real urine. We observed that the internalization efficiency of antibody-modified nanomotors into the spheroids in the presence of urea was significantly higher compared with antibody-modified passive particles or non-targeted nanomotors. Furthermore, cell proliferation studies indicated that targeted, active nanomotors induce higher suppression of spheroid proliferation compared with non-targeted nanomotors, which could be due to a synergistic effect between the inhibition of the fibroblast growth factor pathway by anti-FGFR3 antibody and the local production of ammonia by the active nanomotors. Altogether, these results point towards the applicability of urease-powered nanomotors as tools for enhancing disease detection and simultaneous treatment, by combining improved drug release and targeting functionalities. References (1) Ma, X.; Hortelão, A. C.; Patiño, T.; Sánchez, S. Enzyme Catalysis To Power Micro/Nanomachines. ACS Nano 2016, 10 (10), 9111–9122. https://doi.org/10.1021/acsnano.6b04108. (2) Patiño, T.; Arqué, X.; Mestre, R.; Palacios, L.; Sánchez, S. Fundamental Aspects of Enzyme-Powered Micro- and Nanoswimmers. Acc. Chem. Res. 2018, 51 (11), 2662–2671. https://doi.org/10.1021/acs.accounts.8b00288. (3) Hortelão, A. C.; Patiño, T.; Perez-Jiménez, A.; Blanco, À.; Sánchez, S. Enzyme-Powered Nanobots Enhance Anticancer Drug Delivery. Adv. Funct. Mater. 2018, 28 (25), 1705086. https://doi.org/10.1002/adfm.201705086. (4) Hortelão, A. C.; Carrascosa, R.; Murillo-Cremaes, N.; Patiño, T.; Sánchez, S. Targeting 3D Bladder Cancer Spheroids with Urease-Powered Nanomotors. ACS Nano 2019, 13 (1), 429–439. https://doi.org/10.1021/acsnano.8b06610.

Collective behaviours is a common phenomenon in nature, ranging from microorganisms up to mammalians. The individual interacts with each other exhibiting complex behaviour (swarming or schooling etc.).[1] Here, we report on the collective behaviour of visible light driven Ag/AgCl-based Janus microswimmers surrounded by a dense matrix of passive SiO2 beads in pure water, and quantitative study the dynamics of the Janus and passive beads. The very recent reports have demonstrated, in pure H2O, Ag/AgCl-based Janus microswimmers is of high-mobility [2] and present an efficient exclusive effect to the nearby light polystyrene beads under visible light illumination.[3] These properties benefit from the efficient anisotropic photo-chemical production of the ions and generate a local chemical gradient around the Janus particle,[4] results in exclusion behaviour of dense matrix passive beads. The exclusion effect to the passive beads was found to be much stronger in front of the Ag/AgCl cap than behind the AgCl cap, due to strong flows of the products of the chemical reaction from large clusters. The analysis of this radius of exclusion allows concluding about the asymmetric interactions of a swimmer with passive beads, in front of the AgCl cap and behind it. The observed light-driven exclusion phenomenon could provide a novel insight into the interactive effects between active-passive particles, and offer a better understanding for further biological studies.

The main challenge in designing new generation of plasmonic materials is to produce active materials, i.e. materials which optical properties can be controlled by an external agent [1, 2]. Among the proposed ideas for active control is the combination of plasmonic materials with other functional materials. The combination of magneto-optically (MO) active and plasmonic materials properties has become increasingly appealing, because it gives rise to systems with enhanced optical and MO responses. Moreover, by an adequate choice of the internal structure of such system, plasmonic properties can be controlled by external magnetic field [1, 2]. Our research project is focussed on metamaterials composed of organized chains of selected metal (Cu, Fe) and magnetic oxides (FexOy) NPs, which are expected to exhibit improved magneto-plasmonic properties. The distribution of NPs is controlled during the deposition by means of Inert Gas Condensation technique (IGC) [3], which allows for accurate setting of their size, morphology, chemical composition. Transmission Electron Microscope (TEM) image (Fig. 1a) reveals hybrid NPs deposited on Si3N4 substrate, which have a tendency to form chains. X-ray Photoelectron Spectroscopy (XPS) spectra confirmed the presence of Fe and Cu in NPs and revealed tendency towards oxidation of iron phase. The magnetic response measured by vibrating sample measurement (VSM) shows a significant variation associated with samples composition (iron content) and open hysteresis loops characteristic for ferromagnet or blocked superparamagnet (Fig. 1b). X-ray Absorption Spectroscopy (XAS) measurements revealed surface oxidation of metal particles and a noticeable variation associated with composition and morphology of the hybrids studied. The existence of the plasmonic behaviour of NPs hybrids is proved by increase in Raman signals amplified by surface enhanced Raman scattering (SERS). Proper distribution of anisotropic nano-self-assemblies is expected to provide a way for controlling LSPR, which can be used in nanoantennas, mass storage devices, optical switches or sensors. Acknowledgments The research was financially supported by the National Science Centre, Poland (grant No. 2016/21/D/ST3/00966). References [1] G. Armelles, A. Cebollada, A. Garcia-Martin, et al., Advanced Optical Materials, 1 (2013) 10-35. [2] V. V. Temnov, Nature Photonics 6 (2012) 728-736. [3] A. Kusior, K. Kollbek, K. Kowalski, et al., Applied Surface Science, 380 (2016) 193-202.

The active diffusion of Janus particles interacting with catalytically passive silica beads in narrow channels has been studied in numerical simulations [1] and experiments [2]. Active transport of Janus particles revealed a number of intriguing properties such as self-rectification and autonomous pumping in asymmetric channels [1], directional “locking” and channel “unclogging” [2] whereby a Janus swimmer is capable of transporting large clusters of passive particles [1, 2]. This effect can be used to manipulate colloidal transport in arrays of traps, e.g., to confine passive beads or extract them from the traps [3], by tuning the parameters of the active species. This has potential application in biology and medicine, e.g., to remove dead cells or undesired contaminants from biological systems by means of self-propelled nano-robots. References: [1] P. K. Ghosh, V. R. Misko, F. Marchesoni, and F. Nori, Self-Propelled Janus Particles in a Ratchet: Numerical Simulations, Phys. Rev. Lett. 110, 268301 (2013). [2] H. Yu, A. Kopach, V. R. Misko, A. A. Vasylenko, D. Makarov, F. Marchesoni, F. Nori, L. Baraban, and G. Cuniberti, Confined catalytic Janus swimmers: geometry-driven rectification transients and directional locking, Small 12, 5882-5890 (2016). [3] W. Yang, V. R. Misko, F. Marchesoni, and F. Nori, Colloidal transport through trap arrays controlled by active microswimmers, J. Phys.: Condens. Matter 30, 264004 (2018).

Among the lamellar metal oxides, layered niobates are suitable precursors for nanostructured photocatalysts due to their different structures, band energies, isostructural phase and negative charged layers which allows for intercalation of cationic species. Those materials can be exfoliated by a bulky organic base agent leading to individual niobate nanosheets or even nanoscrolls. In this sense, depending on the desired modification and final application, specific methodologies need to be developed aiming at optimized performances. Thus, in this work, the influence of preparation conditions on the photocatalytic activity of Pt-hexaniobate nanocomposites was investigated. In order to evaluate the influence of the medium and the charge of guest compound, both colloidal hexaniobate suspensions and restacked nanosheets were modified with two different platinum precursors. Modification of hexaniobate layers were carried out by adsorption and impregnation methods, using [Pt(NH)4]Cl2 (Pt1) and H2PtCl6 (Pt2), respectively. The photocatalytic activities of the samples were evaluated by methylene blue photodegradation, methanol photo-oxidation and H2 evolution under UV-light.

CATALIGHT addresses fundamental challenges in the design of photocatalytically active materials for solar energy conversion. Inspired by the design principles of natural photosynthesis, CATALIGHT will provide insights into the performance of molecular photocatalysts embedded in functional and hierarchically structured soft matter materials. General synthetic strategies are developed to tune the reactivity of molecular light-absorbers and catalysts. Complementary synthetic routes are established to access functional polymeric matrices for the site-specific binding of the molecular building blocks. In addition, synergistic reactivity and stability control by tuning the molecule-matrix interactions will become possible. Experimental and theoretical analyses across multiple length- and timescales will be used to rationalize photochemical reactivity and to understand new effects arising from embedding such components within a suitable matrix. Such effects will lead to novel material properties, e.g. materials capable of self-regulating their photocatalytic activity or materials where photocatalytic activity can be repaired both on a molecular and material level. CATALIGHT will lead to new paradigms, which break down the current boundaries between the realms of molecule-based reactivity and bottom-up material design. This will result in fundamentally new, knowledge-guided concepts for light-driven productive chemistry in hybrid materials – opening new research opportunities for chemistry, biology and materials science.

In this work we analyzed the dynamics of particles of 1 mm of diameter. The particles are moved by applying an unsteady magnetic eld at a constant amplitude. Of the preliminary results, we can see that the dynamics of the particles depends of the number of particles in the system. The dynamical properties are obtained employing DDM.

Micromotors with unique spiky morphology were made from sporopollenin exine capsules (SECs). Extracted from sunflower pollen grains, SECs are widely abundant natural materials with shapes of physically robust, highly monodisperse microcapsules. The unique structure ornamented with spiky appendages opens a door to exploring bubble generation on this peculiar biomaterial surface. Bubble-propelled motion of individual SECs was achieved by partial platinum coating on the SEC surface, which enables catalytic decomposition of hydrogen peroxide into oxygen bubbles. Moreover, a large internal cavity provided by the hollow capsule architecture enables macromolecular encapsulation, as proven by the loading and transport of bovine serum albumin.Utilizing the capability of the sporopollenin biopolymer’s to bind with heavy metal,the SECs micromotors could serves as microcleaners to remove pollutants. The fluid mixing induced by the motion and bubble generation dramatically enhance the removal efficiency. Coupling the advantageous properties of SECs with autonomous motion ability, the bioinspired micromotors offers a multifunctional platform for drug delivery and water remediation applications.

Significant efforts have been made recently towards development of light-driven micromotors. TiO2 has been used as base material for light driven microswimmers owing to efficient activity, enviromental benigity, low-cost and chemical stability. We introduce asymmetry by deposition of metal layers and observed the behaviours. Based on the different motion mechanisms in variours conditions, (water+UV light, peroxide+visible light, peroxide+UV light), it shows different interaction behaviours between active Janus TiO2 and passive particles. Especially, in peroxide with UV light, it displays strong attractive phoretic interactions, which can induce certain pattern formation in passive particles. These crystalline clusters can actively move together, see model and example in Fig. 1. Later, this interaction was applied to different passive particles, proving its robustness, including PS and microparticles from daily life (tooth paste, washing powder). Finaly, it has been successfuly applied for microplastics removal from water in laboratory scale. Fig.1 Scheme and optical images of interaction between TiO2 based micromotors and PS particles [1] Wang, Linlin; Kaeppler, Andrea; Fischer, Dieter; Simmchen, Juliane (2019): Photocatalytic TiO2 Micromotors for Removal of Microplastics and Suspended Matter. ChemRxiv. Preprint. doi.org/10.26434/chemrxiv.7959182.v1

Self-motile mesoporous ZnO/Pt-based Janus micromotors accelerated by bubble propulsion that provide efficient removal of explosives and dye pollutants via photodegradation under visible light are presented. Decomposition of H2O2 (the fuel) is triggered by a platinum catalytic layer asymmetrically deposited on the nanosheets of the hierarchical and mesoporous ZnO microparticles. The size-dependent motion behavior of the mesoporous micromotors is studied; the micromotors with average size ∼1.5 μm exhibit enhanced self-diffusiophoretic motion, whereas the fast bubble propulsion is detected for micromotors larger than 5 μm. The bubble-propelled mesoporous ZnO/Pt Janus micromotors show remarkable speeds of over 350 μm s–1 at H2O2 concentrations lower than 5 wt %, which is unusual for Janus micromotors based on dense materials such as ZnO. This high speed is related to efficient bubble nucleation, pinning, and growth due to the highly active and rough surface area of these micromotors, whereas the ZnO/Pt particles with a smooth surface and low surface area are motionless. We discovered new atomic interfaces of ZnO2 introduced into the ZnO/Pt micromotor system, as revealed by X-ray diffraction (XRD), which contribute to enhance their photocatalytic activity under visible light. Such coupling of the rapid movement with the high catalytic performance of ZnO/Pt Janus micromotors provides efficient removal of nitroaromatic explosives and dye pollutants from contaminated water under visible light without the need for UV irradiation. This paves the way for real-world environmental remediation efforts using microrobots.