Mechanical Coupling of Puller and Pusher Active Microswimmers Influences Motility.

Active self-propelled colloidal populations induce time-dependent three-dimensional fluid flows, which alter the rheological (viscoelastic) properties of their fluidic media. Researchers have also studied passive colloids mixed with bacterial suspensions to understand the hydrodynamic coupling between active and passive colloids. With recent developments in biological cell-driven biohybrid microswimmers, different type biological microswimmer (e.g., bacteria and algae) populations need to interact fluidically with each other in the same fluidic media, while such interactions have not been studied experimentally yet. Therefore, we report the swimming behavior of two opposite types of biological microswimmer (active colloid) populations: Chlamydomonas reinhardtii (C. reinhardtii) algae (puller-type microswimmers) population in coculture with Escherichia coli (E. coli) bacteria (pusher-type microswimmers) population. We observed noticeable fluidic coupling deviations from the existing understanding of passive colloids mixed with bacterial suspensions previously studied in the literature. The fluidic coupling among puller- and pusher-type microswimmers led to nonequilibrium fluctuations in the fluid flow due to their opposite swimming patterns. Such coupling could be the main reason behind the shift in motility behaviors of these two opposite-type swimmer populations suspended in the same fluidic media.

Bioinspired synthesis of SnO crosses as backbone in artificial sponges.

The distinct electronic properties, including p-type semiconducting and a wide optical band gap, renders SnO suitable for applications such as microelectronic devices, gas sensors and electrodes. However, the synthesis of SnO is rather challenging due to the instability of the oxide, which is usually obtained as a by-product of SnO2 fabrication. In this work, we developed a bioinspired synthesis, based on a hydrothermal approach, for the direct production of SnO nanoparticles. The amount of mineralizer, inducing the precipitation, was identified, which supports a template-free formation of the nanosized SnO particles at low temperature and mild chemical conditions. Moreover, the SnO nanoparticles exhibit a shape of unique three-dimensional crosses similar to the calcite crosses present in the calcareous sponges. We demonstrated that SnO crosses are evenly distributed and embedded in an organic scaffold by an ice-templating approach, in this way closely mimicking the structure of calcareous sponges. Such scaffolds, reinforced by an active material, here SnO, could be used as filters, sensors or electrodes, where a high surface area and good accessibility are essential. This article is part of the theme issue 'Bioinspired materials and surfaces for green science and technology (part 2)'.

Peptide-Induced Biomineralization of Tin Oxide (SnO2) Nanoparticles for Antibacterial Applications.

Recently, there has been growing attention and effort to search for new microbicidal drugs which present different mode of action from those already existing, as an alternative to the global threat of fungal and bacterial multi drug resistance (MDR). Here we propose biological synthesis of SnO2 nanoparticles using mammalian cells as an economic and ecofriendly platform. This presents a novel biogenic method for SnO2 synthesis using metal binding peptides extracted from MCF-7 human cancer cells, which induces the biomineralization of SnO2 nanoparticles. A series of electron donor functional groups and metal binding sites in these peptides reacts with Sn2+ ions and directs the growth of SnO2 nanoparticles without addition of toxic redox and capping agents in the reaction system. Since peptides present reactive sites in aqueous solution at room temperature, a facile reaction environment can be easily achieved. Furthermore, by tuning the reactants' concentration and pH, the size, shape and 3D-structures of SnO2 nanoparticles can be controlled. Peptides also ensure biocompatibility, and SnO2 nanoparticles provide antibacterial properties, which broadens their applications in biomedical fields.

Ultrahigh Damping Capacities in Lightweight Structural Materials.

The demand to outperform current technologies pushes scientists to develop novel strategies, which enable the fabrication of materials with exceptional properties. Along this line, lightweight structural materials are of great interest due to their versatile applicability as sensors, catalysts, battery electrodes, and acoustic or mechanical dampers. Here, we report a strategy to design ultralight (ρ = 3 mg/cm3) and hierarchically structured ceramic scaffolds of macroscopic size. Such scaffolds exhibit mechanical reversibility comparable to that of microscopic metamaterials, leading to a macroscopically remarkable dynamic mechanical performance. Upon mechanical loading, these scaffolds show a deformation mechanism similar to polyurethane foams, and this resilience yields ultrahigh damping capacities, tan δ, of up to 0.47.

Review of emerging concepts in nanotoxicology: opportunities and challenges for safer nanomaterial design.

Nanotoxicology and nanosafety has been a topic of intensive research for about more than 20 years. Nearly 10 000 research papers have been published on the topic, yet there exists a gap in terms of understanding and ways to harmonize nanorisk assessment. In this review, we revisit critically ignored parameters of nanoscale materials (e.g. band gap factor, phase instability and silver leaching problem, defect and instability plasmonic versus inorganic particles) versus their biological counterparts (cell batch-to-batch heterogeneity, biological barrier model design, cellular functional characteristics) which yield variability and nonuniformity in results. We also emphasize system biology approaches to integrate the high throughput screening methods coupled with in vivo and in silico modeling to ensure quality in nanosafety research. We emphasize and highlight the recommendation regarding bridging the mechanistic gaps in fundamental research and predictive biological response in nanotoxicology. The research community has to develop visions to predict the unforeseen problems that do not exist yet in context with nanotoxicity and public health hazards due to the burgeoning use of nanomaterial in consumer's product.

Incorporation of zinc into the coccoliths of the microalga Emiliania huxleyi.

The coccolithophore Emiliania huxleyi is covered with elaborated calcite plates, the so-called coccoliths, which are produced inside the cells. We investigated the incorporation of zinc into the coccoliths of E. huxleyi by applying different zinc and calcium amounts via the culture media and subsequently analyzing the zinc content in the cells and the Zn/Ca ratio of the coccoliths. To investigate the Zn/Ca ratio of coccoliths built in the manipulated media, the algae have first to be decalcified, i.e. coccolith free. We used a newly developed decalcification method to obtain 'naked' cells for cultivation. E. huxleyi proliferated and produced new coccoliths in all media with manipulated Zn/Ca ratios. The cells and the newly built coccoliths were investigated regarding their zinc content and their Zn/Ca ratio, respectively. High zinc amounts were taken up by the algae. The Zn/Ca ratio of the coccoliths was positively correlated to the Zn/Ca ratio of the applied media. The unique feature of the coccoliths was maintained also at high Zn/Ca ratios. We suggest the following pathway of the zinc ions into the coccoliths: first, the zinc ions are bound to the cell surface, followed by their transportation into the cytoplasm. Obviously, the zinc ions are removed afterwards into the coccolith vesicle, where the zinc is incorporated into the calcite coccoliths which are then extruded. The incorporation of toxic zinc ions into the coccoliths possibly due to a new function of the coccoliths as detoxification sites is discussed.

Generation of Multishell Magnetic Hybrid Nanoparticles by Encapsulation of Genetically Engineered and Fluorescent Bacterial Magnetosomes with ZnO and SiO2.

Magnetic nanoparticles (MNPs) have great potential in biomedical applications, but the chemical synthesis of size-controlled and functionalized core-shell MNPs remain challenging. Magnetosomes produced by the magnetotactic bacterium Magnetospirillum gryphiswaldense are naturally uniform and chemically pure magnetite MNPs with superior magnetic characteristics. Here, additional functionalities are made possible by the incorporation of biomolecules on the magnetosome surface; the magnetosome system is then chemically encapsulated with an inorganic coating. The novel multishell nanoparticles consist of the magnetosome core-which includes the magnetite crystal, the magnetosome membrane, and additional moieties, such as the enhanced green fluorescent protein (EGFP) and peptides-and an outer shell, comprising either silica or zinc oxide. Coating the functionalized magnetosomes with silica improves their colloidal stability and preserves the EGFP fluorescence in the presence of proteases and detergents. In addition, the surface charge of magnetosomes can be adjusted by varying the coating. This method will be useful for the versatile generation of new, multifunctional, multishell, and magnetic hybrid nanomaterials with potential applications in various biotechnological fields.

Genetically improved monolayer-forming tobacco mosaic viruses to generate nanostructured semiconducting bio/inorganic hybrids.

The genetically determined design of structured functional bio/inorganic materials was investigated by applying a convective assembly approach. Wildtype tobacco mosaic virus (wt TMV) as well as several TMV mutants were organized on substrates over macroscopic-length scales. Depending on the virus type, the self-organization behavior showed pronounced differences in the surface arrangement under the same convective assembly conditions. Additionally, under varying assembly parameters, the virus particles generated structures encompassing morphologies emerging from single micrometer long fibers aligned parallel to the triple-contact line through disordered but dense films to smooth and uniform monolayers. Monolayers with diverse packing densities were used as templates to form TMV/ZnO hybrid materials. The semiconducting properties can be directly designed and tuned by the variation of the template architecture which are reflected in the transistor performance.

Adsorption and self-assembly of M13 phage into directionally organized structures on C and SiO2 films.

A versatile method for the directional assembly of M13 phage using amorphous carbon and SiO2 thin films was demonstrated. A high affinity of the M13 phage macromolecules for incorporation into aligned structures on an amorphous carbon surface was observed at the concentration range, in which the viral nanofibers tend to disorder. In contrast, the viral particles showed less freedom to adopt an aligned orientation on SiO2 films when deposited in close vicinity. Here an interpretation of the role of the carbon surface in significant enhancement of adsorption and generation of viral arrays with a high orientational order was proposed in terms of surface chemistry and competitive electrostatic interactions. This study suggests the use of amorphous carbon substrates as a template for directional organization of a closely-packed and two-dimensional M13 viral film, which can be a promising route to mineralize a variety of smooth and homogeneous inorganic nanostructure layers.

Harmonization Risks and Rewards: Nano-QSAR for Agricultural Nanomaterials.

This comprehensive review explores the emerging landscape of Nano-QSAR (quantitative structure-activity relationship) for assessing the risk and potency of nanomaterials in agricultural settings. The paper begins with an introduction to Nano-QSAR, providing background and rationale, and explicitly states the hypotheses guiding the review. The study navigates through various dimensions of nanomaterial applications in agriculture, encompassing their diverse properties, types, and associated challenges. Delving into the principles of QSAR in nanotoxicology, this article elucidates its application in evaluating the safety of nanomaterials, while addressing the unique limitations posed by these materials. The narrative then transitions to the progression of Nano-QSAR in the context of agricultural nanomaterials, exemplified by insightful case studies that highlight both the strengths and the limitations inherent in this methodology. Emerging prospects and hurdles tied to Nano-QSAR in agriculture are rigorously examined, casting light on important pathways forward, existing constraints, and avenues for research enhancement. Culminating in a synthesis of key insights, the review underscores the significance of Nano-QSAR in shaping the future of nanoenabled agriculture. It provides strategic guidance to steer forthcoming research endeavors in this dynamic field.

Genesis of amorphous calcium carbonate containing alveolar plates in the ciliate Coleps hirtus (Ciliophora, Prostomatea).

In the protist world, the ciliate Coleps hirtus (phylum Ciliophora, class Prostomatea) synthesizes a peculiar biomineralized test made of alveolar plates, structures located within alveolar vesicles at the cell cortex. Alveolar plates are arranged by overlapping like an armor and they are thought to protect and/or stiffen the cell. Although their morphology is species-specific and of complex architecture, so far almost nothing is known about their genesis, their structure and their elemental and mineral composition. We investigated the genesis of new alveolar plates after cell division and examined cells and isolated alveolar plates by electron microscopy, energy-dispersive X-ray spectroscopy, FTIR and X-ray diffraction. Our investigations revealed an organic mesh-like structure that guides the formation of new alveolar plates like a template and the role of vesicles transporting inorganic material. We further demonstrated that the inorganic part of the alveolar plates is composed out of amorphous calcium carbonate. For stabilization of the amorphous phase, the alveolar vesicles, the organic fraction and the element phosphorus may play a role.

Fast One-Step Fabrication of Highly Regular Microscrolls with Controllable Surface Morphology.

Although rolling origami technology has provided convenient access to three-dimensional (3D) microstructure systems, the high yield and scalable construction of complex rolling structures with well-defined geometry without impeding functionality has remained challenging. The straightforward, one-step fabrication that uses external mechanical stress to scroll micrometer thick, flexible planar films with centimeter lateral dimensions into tubular or spiral geometry within a few seconds is demonstrated. The method allows controlling the scrolls' diameter, number of windings and nanostructured surface morphology, and is applicable to a wide range of functional materials. The obtained 3D structures are highly promising for various applications including sensors, actuators, microrobotics, as well as energy storage and electronic devices.

In Situ Ultra-Small- and Small-Angle X-ray Scattering Study of ZnO Nanoparticle Formation and Growth through Chemical Bath Deposition in the Presence of Polyvinylpyrrolidone.

ZnO inverse opals combine the outstanding properties of the semiconductor ZnO with the high surface area of the open-porous framework, making them valuable photonic and catalysis support materials. One route to produce inverse opals is to mineralize the voids of close-packed polymer nanoparticle templates by chemical bath deposition (CBD) using a ZnO precursor solution, followed by template removal. To ensure synthesis control, the formation and growth of ZnO nanoparticles in a precursor solution containing the organic additive polyvinylpyrrolidone (PVP) was investigated by in situ ultra-small- and small-angle X-ray scattering (USAXS/SAXS). Before that, we studied the precursor solution by in-house SAXS at T = 25 °C, revealing the presence of a PVP network with semiflexible chain behavior. Heating the precursor solution to 58 °C or 63 °C initiates the formation of small ZnO nanoparticles that cluster together, as shown by complementary transmission electron microscopy images (TEM) taken after synthesis. The underlying kinetics of this process could be deciphered by quantitatively analyzing the USAXS/SAXS data considering the scattering contributions of particles, clusters, and the PVP network. A nearly quantitative description of both the nucleation and growth period could be achieved using the two-step Finke-Watzky model with slow, continuous nucleation followed by autocatalytic growth.

Recent Advances in Nano-Enabled Seed Treatment Strategies for Sustainable Agriculture: Challenges, Risk Assessment, and Future Perspectives.

Agro seeds are vulnerable to environmental stressors, adversely affecting seed vigor, crop growth, and crop productivity. Different agrochemical-based seed treatments enhance seed germination, but they can also cause damage to the environment; therefore, sustainable technologies such as nano-based agrochemicals are urgently needed. Nanoagrochemicals can reduce the dose-dependent toxicity of seed treatment, thereby improving seed viability and ensuring the controlled release of nanoagrochemical active ingredients However, the applications of nanoagrochemicals to plants in the field raise concerns about nanomaterial safety, exposure levels, and toxicological implications to the environment and human health. In the present comprehensive review, the development, scope, challenges, and risk assessments of nanoagrochemicals on seed treatment are discussed. Moreover, the implementation obstacles for nanoagrochemicals use in seed treatments, their commercialization potential, and the need for policy regulations to assess possible risks are also discussed. Based on our knowledge, this is the first time that we have presented legendary literature to readers in order to help them gain a deeper understanding of upcoming nanotechnologies that may enable the development of future generation seed treatment agrochemical formulations, their scope, and potential risks associated with seed treatment.

Functional mimicry of sea urchin biomineralization proteins with CaCO3-binding peptides selected by phage display.

The intricate process of biomineralization, e.g. in sea urchins, involves the precise interplay of highly regulated mineralization proteins and the spatiotemporal coordination achieved through compartmentalization. However, the investigation of biomineralization effector molecules, e.g. proteins, is challenging, due to their very low abundance. Therefore, we investigate the functional mimicry in the bioinspired precipitation of calcium carbonate (CaCO3) with artificial peptides selected from a peptide library by phage display based on peptide-binding to calcite and aragonite, respectively. The structure-directing effects of the identified peptides were compared to those of natural protein mixes isolated from skeletal (test) structures of two sea urchin species (Arbacia lixula and Paracentrotus lividus). The calcium carbonate samples deposited in the absence or presence of peptides were analyzed with a set of complementary techniques with regard to morphology, polymorph, and nanostructural motifs. Remarkably, some of the CaCO3-binding peptides induced morphological features in calcite that appeared similar to those obtained in the presence of the natural protein mixes. Many of the peptides identified as most effective in exerting a structure-directing effect on calcium carbonate crystallization were rich in basic amino acid residues. Hence, our in vitro mineralization study further highlights the important, but often neglected, role of positively charged soluble organic matrices associated with biological and bioinspired CaCO3 deposition.

Digital Transformation in Toxicology: Improving Communication and Efficiency in Risk Assessment.

Toxicology is undergoing a digital revolution, with mobile apps, sensors, artificial intelligence (AI), and machine learning enabling better record-keeping, data analysis, and risk assessment. Additionally, computational toxicology and digital risk assessment have led to more accurate predictions of chemical hazards, reducing the burden of laboratory studies. Blockchain technology is emerging as a promising approach to increase transparency, particularly in the management and processing of genomic data related with food safety. Robotics, smart agriculture, and smart food and feedstock offer new opportunities for collecting, analyzing, and evaluating data, while wearable devices can predict toxicity and monitor health-related issues. The review article focuses on the potential of digital technologies to improve risk assessment and public health in the field of toxicology. By examining key topics such as blockchain technology, smoking toxicology, wearable sensors, and food security, this article provides an overview of how digitalization is influencing toxicology. As well as highlighting future directions for research, this article demonstrates how emerging technologies can enhance risk assessment communication and efficiency. The integration of digital technologies has revolutionized toxicology and has great potential for improving risk assessment and promoting public health.

Isolation of ZnO-binding 12-mer peptides and determination of their binding epitopes by NMR spectroscopy.

Inorganic-binding peptides are in the focus of research fields such as materials science, nanotechnology, and biotechnology. Applications concern surface functionalization by the specific coupling to inorganic target substrates, the binding of soluble molecules for sensing applications, or biomineralization approaches for the controlled formation of inorganic materials. The specific molecular recognition of inorganic surfaces by peptides is of major importance for such applications. Zinc oxide (ZnO) is an important semiconductor material which is applied in various devices. In this study the molecular fundamentals for a ZnO-binding epitope was determined. 12-mer peptides, which specifically bind to the zinc- or/and the oxygen-terminated sides of single-crystalline ZnO (0001) and (000-1) substrates, were selected from a random peptide library using the phage display technique. For two ZnO-binding peptides the mandatory amino acid residues, which are of crucial importance for the specific binding were determined with a label-free nuclear magnetic resonance (NMR) approach. NMR spectroscopy allows the identification of pH dependent interaction sites on the atomic level of 12-mer peptides and ZnO nanoparticles. Here, ionic and polar interaction forces were determined. For the oxygen-terminated side the consensus peptide-binding sequence (HSXXH) was predicted in silico and confirmed by the NMR approach.

Adsorption of azide-functionalized thiol linkers on zinc oxide surfaces.

A comprehensive understanding of the interactions between organic molecules and a metal oxide surface is essential for an efficient surface modification and the formation of organic-inorganic hybrids with technological applications ranging from heterogeneous catalysis and biomedical templates up to functional nanoporous matrices. In this work, first-principles calculations supported by experiments are used to provide the microstructural characteristics of (101̄0) surfaces of zinc oxide single crystals modified by azide terminated hydrocarbons, which graft on the oxide through a thiol group. On the computational side, we evaluate the specific interactions between the surface and the molecules with the chemical formula N3(CH2) n SH, with n = 1, 3, 6, 9. We demonstrate that the molecules chemisorb on the bridge site of ZnO(101̄0). Upon adsorption, the N3(CH2) n SH molecules break the neutral (Zn δ+-O δ-) dimers on ZnO(101̄0) resulting in a structural distortion of the ZnO(101̄0) substrate. The energy decomposition analysis revealed that such structure distortion favors the adsorption of the molecules on the surface leading to a strong correlation between the surface distortion energy and the interaction energy of the molecule. An azide-terminated thiol with three methylene groups in the hydrocarbon chain N3(CH2)3SH was synthesized, and the assembly of this linker on ZnO surfaces was confirmed through atomic force microscopy. The bonding to the inorganic surface was examined via X-ray photoelectron spectroscopy (XPS). Clear signatures of the organic components on the oxide substrates were observed underlying the successful realization of thiol-grafting on the metal oxide. Temperature-dependent and angle-resolved XPS were applied to examine the thermal stability and to determine the thickness of the grafted SAMs, respectively. We discuss the high potential of our hybrid materials in providing further functionalities towards heterocatalysis and medical applications.

Self-supporting V2O5 nanofiber-based electrodes for magnesium-lithium-ion hybrid batteries.

The increasing demand for high energy, sustainable and safer rechargeable electrochemical storage systems for portable devices and electric vehicles can be satisfied by the use of hybrid batteries. Hybrid batteries, such as magnesium-lithium-ion batteries (MLIBs), using a dual-salt electrolyte take advantage of both the fast Li+ intercalation kinetics of lithium-ion batteries (LIBs) and the dendrite-free anode reactions. Here we report the utilization of a binder-free and self-supporting V2O5 nanofiber-based cathode for MLIBs. The V2O5 cathode has a high operating voltage of ∼1.5 V vs. Mg/Mg2+ and achieves storage capacities of up to 386 mA h g-1, accompanied by an energy density of 280 W h kg-1. Additionally, a good cycling stability at 200 mA g-1 over 500 cycles is reached. The structural integrity of the V2O5 cathode is preserved upon cycling. This work demonstrates the suitability of the V2O5 cathode for MLIBs to overcome the limitations of LIBs and MIBs and to meet the future demands of advanced electrochemical storage systems.

Templated self-assembly of ZnO films on monolayer patterns with nanoscale resolution.

Lithographically defined self-growing ZnO films were prepared by a bioinspired chemical bath deposition technique (CBD). We observed a high selectivity of ZnO deposition: Teflon-like per-fluoro-decyl-trichlorosilane (FDTS) monolayers repelled ZnO primary particles, whereas amino-functionalized areas of the substrate were selectively covered by a highly anisotropic, oriented, and compact ZnO film with a thickness of 50 nm. The size of the primary particles in our methanol-based solution was approximately 2.5 nm. On the amino substrate they formed agglomerates not larger than 30 nm. Monolayer patterns made by polymer blend lithography were templated with an edge resolution of 30 nm. By using a specialized derivative of microcontact printing, we prepared layout-defined silane templates, which reliably determined the growth of a layout-defined, patterned oxide film with submicrometer lateral resolution.