Search

The interaction between bacteria and nanomaterials, particularly from a physical or mechanical perspective, has emerged as a topic of significant interest in both science and medicine. Mechanobactericidal nanomaterials, which exert antimicrobial effects through purely physical mechanisms, hold promise as alternative strategies to combat bacterial resistance to traditional antibiotics. High-aspect-ratio nanoparticles and surface topographies are being engineered to enhance their mechanobactericidal properties. However, progress in this field is hindered by an incomplete understanding of how these materials induce mechanical cell death in bacteria. This review examines the role of atomic force microscopy (AFM) nanoindentation in quantifying forces required to rupture the bacterial cell wall. The reported values range from nN to a few tens of nN, depending on the type of bacterium and the experimental conditions used. The potential effect of AFM tip properties, loading speed, bacterial immobilization strategy, or environmental conditions on the measured rupture values are discussed. This perspective also highlights the complexities of modeling bacterial cell rupture and the importance of pressure as a parameter for standardizing results across experiments. Furthermore, the implications of these quantitative insights to understand the mechanisms of action of mechanobactericidal nanomaterials are discussed., (© 2024 Wiley‐VCH GmbH.)

Hydrogels, three-dimensional hydrophilic polymeric networks with high water retaining capacity, have gained prominence in wound management and drug delivery due to their tunability, softness, permeability, and biocompatibility. Electron-beam polymerized poly(ethylene glycol) diacrylate (PEGDA) hydrogels are particularly useful for phototherapies such as antimicrobial photodynamic therapy (aPDT) due to their excellent optical properties. This work takes advantage of the transparency of PEGDA hydrogels to investigate bacterial responses to aPDT at the single-cell level, in real-time and in situ . The photosensitizer methylene blue (MB) was loaded in PEGDA hydrogels by using two methods: reversible loading and irreversible immobilization within the 3D polymer network. MB release kinetics and singlet oxygen generation were studied, revealing the distinct behaviors of both hydrogels. Real-time imaging of Escherichia coli was conducted during aPDT in both hydrogel types, using the Min protein system to report changes in bacterial physiology. Min oscillation patterns provided mechanistic insights into bacterial photoinactivation, revealing a dependence on the hydrogel preparation method. This difference was attributed to the mobility of MB within the hydrogel, affecting its direct interaction with bacterial membranes. These findings shed light on the complex interplay between hydrogel properties and the bacterial response during aPDT, offering valuable insights for the development of antibacterial wound dressing materials. The study demonstrates the capability of real-time, single-cell fluorescence microscopy to unravel dynamic bacterial behaviors in the intricate environment of hydrogel surfaces during aPDT.

Min oscillations are a fascinating mechanism used by Escherichia coli to find their middle. Beyond their biological role, they provide a convenient and relatively unexplored method to monitor the effect of sublethal environmental challenges on bacterial physiology in real-time and at the single-cell level. In this review, we discuss the original papers that put forward the idea of using Min oscillations as a reporting tool to monitor the effect of extracellular cationic compounds, including antibiotics. More recent work from our laboratory explores this tool to follow bacterial response to other challenges such as weak mechanical interactions with nanomaterials or photodynamic treatment. We discuss the physiological meaning of the changes in Min oscillation period, likely related to membrane potential dynamics, as well as the benefits and limitations of using oscillations as a reporter in fluorescence microscopy. Overall, Min oscillations are a useful addition to the fluorescence microscopy toolbox in order to visualize stress responses in E. coli , and have the potential to provide full mechanistic understanding of the events that lead to bacterial cell death in different contexts.

We performed a time-lapse imaging with atomic force microscopy (AFM) of the motion of eukaryotic CRFK (Crandell-Rees Feline Kidney) cells adhered onto a glass surface and anchored to other cells in culture medium at 37 °C. The main finding is a gradient in the spring constant of the actomyosin cortex along the cells axis. The rigidity increases at the rear of the cells during motion. This observation as well as a dramatic decrease of the volume suggests that cells may organize a dissymmetry in the skeleton network to expulse water and drive actively the rear edge.

CRANAD-2 is a fluorogenic curcumin derivative used for near-infrared detection and imaging in vivo of amyloid aggregates, which are involved in neurodegenerative diseases. We explore the performance of CRANAD-2 in two super-resolution imaging techniques, namely stimulated emission depletion (STED) and single-molecule localization microscopy (SMLM), with markedly different fluorophore requirements. By conveniently adapting the concentration of CRANAD-2, which transiently binds to amyloid fibrils, we show that it performs well in both techniques, achieving a resolution in the range of 45-55 nm. Correlation of SMLM with atomic force microscopy (AFM) validates the resolution of fine features in the reconstructed super-resolved image. The good performance and versatility of CRANAD-2 provides a powerful tool for near-infrared nanoscopic imaging of amyloids in vitro and in vivo., (© 2022 Wiley-VCH GmbH.)

The Min protein system is a cell division regulator in Escherichia coli . Under normal growth conditions, MinD is associated with the membrane and undergoes pole-to-pole oscillations. The period of these oscillations has been previously proposed as a reporter for the bacterial physiological state at the single-cell level and has been used to monitor the response to sublethal challenges from antibiotics, temperature, or mechanical fatigue. Using real-time single-cell fluorescence imaging, we explore here the effect of photodynamic treatment on MinD oscillations. Irradiation of bacteria in the presence of the photosensitizer methylene blue disrupts the MinD oscillation pattern depending on its concentration. In contrast to antibiotics, which slow down the oscillation, photodynamic treatment results in an abrupt interruption, reflecting divergent physiological mechanisms leading to bacterial death. We show that MinD oscillations are sensitive to mild photodynamic effects that are overlooked by traditional methods, expanding the toolbox for mechanistic studies in antimicrobial photodynamic therapy.

Tumor-on-chip devices are becoming ideal platforms to recreate in vitro the particular physiological microenvironment of interest for onco-nanomedicine testing and development. This work presents a strategy to produce a round artificial microvessel on-a-chip device for the study of physiologically relevant nanomedicine transport dynamics. The microchannels have a diameter in the range of the tumor capillaries and a semicircular geometry. This geometry is obtained through an intermediate thermal nanoimprint step using a master mold with square-shaped channel structures produced by standard silicon micromachining or by stereolithography three-dimensional (3D) printing. The working microfluidic chip devices are made by casting polydimethylsiloxane on the imprinted intermediate mold. Artificial blood microvessels are created by seeding human endothelial cells into the round-shaped channels acting as the scaffold. The microchip is connected by 3D-printed reservoirs to a pressure controller, allowing for a fine fluidic control. Under physiological flow conditions, the dynamic interaction of nanoparticles (NPs) with the artificial endothelium was assessed by high-magnification fluorescence microscopy. Overtime, internalization of NPs and clustering was observed and the accumulation rate into the endothelial cells could be characterized in real time., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

We report that Thioflavin T (ThT), the reference fluorogenic probe for amyloid detection, displays photodynamic activity against bacterial biofilms. ThT recognizes key structures of the biofilm matrix, disrupting the complex architecture and efficiently inactivating bacterial cells. We also show that ThT phototherapy synergistically boosts the activity of conventional antimicrobials.

The thermal stability of antireflective moth-eye topographical features fabricated by nanoimprint lithography on poly (methyl methacrylate) (PMMA) incorporating TiO 2 nanoparticles is explored. The effect of nanoparticle load on the relaxation dynamics of the moth-eye nanostructure is evaluated via grazing incidence small angle x-ray scattering measurements by in situ monitoring the structural decay of the nanopatterns upon thermal annealing. It is demonstrated that the incorporation of TiO 2 nanoparticles to the imprinted surface nanocomposite films delays greatly the pattern relaxation which, in turn, enhances the stability of the patterned topography even at temperatures well above the polymer glass transition (T g ). The improved thermal behavior of the antireflective films will significantly enhance their functionality and performance in light-trapping applications where temperatures typically rise, such as solar devices or solar glass panels., (© 2021 IOP Publishing Ltd.)

Temperature measurement at the nanoscale has brought insight to a wide array of research interests in modern chemistry, physics, and biology. These measurements have been enabled by the advent of nanothermometers, which relay nanoscale temperature information through the analysis of their intrinsic photophysical behavior. In the past decade, several nanothermometers have been developed including dyes, nanodiamonds, fluorescent proteins, nucleotides, and nanoparticles. However, temperature measurement using intact DNA has not yet been achieved. Here, we present a method to study the temperature sensitivity of the DNA molecule within a physiologic temperature range when complexed with fluorescent dye. We theoretically and experimentally report the temperature sensitivity of the DNA-Hoechst 33342 complex in different sizes of double-stranded oligonucleotides and plasmids, showing its potential use as a nanothermometer. These findings allow for extending the thermal study of DNA to several research fields including DNA nanotechnology, optical tweezers, and DNA nanoparticles., (© 2020 Wiley-VCH GmbH.)

This work describes the fabrication process of moth eye antireflective poly (methyl methacrylate) transparent films via roll to roll thermal nanoimprint lithography. The process parameters are investigated and adjusted in order to obtain from a single moth-eye structured mold, a range of antireflective topographies that gradually vary their geometry from protruding to intruding nanocones. A correlation between the process parameters with the optical and mechanical properties of the films is established to illustrate the influence of the processing parameters and serve as guideline to produce antireflective flexible films with balanced properties and optimized performance adequate to the application environment. A finite element model is described predicting the mechanical behavior of the moth-eye PMMA imprinted nanostructures.

Singlet oxygen ( 1 O 2 ) is the first electronic excited state of molecular oxygen. Due to its non-radical and non-ionic character as well as its mild reactivity, 1 O 2 has a pivotal role in cell signaling processes at low concentration, yet it is cytotoxic at high concentrations. Quantifying the production of 1 O 2 , particularly in biological systems, is therefore essential for understanding and controlling its effects. 1 O 2 can be produced by chemical and biological reactions, yet its most common method of production is by photosensitization, whereby an initially photoexcited molecule transfers its acquired electronic energy to the dioxygen molecule. The efficiency of this process is characterized by the 1 O 2 production quantum yield, Φ Δ , which can be determined by directly monitoring its intrinsic weak near-infrared phosphorescence or indirectly by trapping it with a suitable acceptor, a process that can be monitored by common analytical techniques. Indirect methods are thus very popular, yet they may lead to severe errors if used incorrectly. Herein we describe the common aspects of indirect methods and propose a general step-by-step procedure for the determination of Φ Δ values. In addition, we identify the key experimental conditions that need to be controlled to obtain meaningful results.

We report the use of the amyloid probe Thioflavin T (ThT) as a specific and exchangeable fluorophore for stimulated emission depletion (STED) super-resolution imaging of amyloid fibers. This method achieves a spatial resolution in the range of 60-70 nm, low image background and increased photostability that enables long-term STED imaging. These results expand the widespread uses of ThT and can be potentially extended to other common amyloid fluorescent probes, providing new tools for the study of amyloid diseases.

Mechano-bactericidal nanomaterials rely on their mechanical or physical interactions with bacteria and are promising antimicrobial strategies that overcome bacterial resistance. However, the real effect of mechanical versus chemical action on their activity is under debate. In this paper, we quantify the forces necessary to produce critical damage to the bacterial cell wall by performing simultaneous nanoindentation and fluorescence imaging of single bacterial cells. Our experimental setup allows puncturing the cell wall of an immobilized bacterium with the tip of an atomic force microscope (AFM) and following in real time the increase in the fluorescence signal from a cell membrane integrity marker. We correlate the forces exerted by the AFM tip with the fluorescence dynamics for tens of cells, and we find that forces above 20 nN are necessary to exert critical damage. Moreover, a similar experiment is performed in which bacterial viability is assessed through physiological activity, in order to gain a more complete view of the effect of mechanical forces on bacteria. Our results contribute to the quantitative understanding of the interaction between bacteria and nanomaterials.

A combination of time-resolved optical spectroscopy and nanoscale imaging has been used to study the complex binding to amyloids of a photocatalyst that selectively photo-oxygenates pathogenic aggregates, as well as the consequences of its irradiation. Correlative atomic force microscopy (AFM) and fluorescence microscopy reveals topography-dependent binding of the dye to model β-lactoglobulin fibers, which may also explain the observed difference in their response to photodegradation. We provide direct evidence of the photosensitization of singlet oxygen by the photocatalyst bound to amyloid fibers by direct detection of its NIR phosphorescence. The effect of singlet oxygen at the molecular level brings about nanoscale morphological changes that can be observed with AFM at the single-fiber level. We also find differential response of two α-synuclein mutants to photodamage, which can be rationalized by the presence of amino acids susceptible to photo-oxygenation. Overall, our results help to unravel some of the complexity associated with highly heterogeneous amyloid populations and contribute to the development of improved phototherapeutic strategies for amyloid-related disorders.

Luminescent metal-organic frameworks (LMOFs) are promising materials for lighting and sensing applications. Herein, exposure of the highly luminescent Zn 2 (bpdc) 2 (bpee) MOF (H 2 bpdc = 4,4'-biphenyldicarboxylic acid and bpee = 1,2-bipyridylethene) to subppm amine contents turns on a new absorption band unambiguously ascribed to free bpee molecules concomitant with the gradual appearance of a new photoluminescence band at shorter wavelengths. These findings combined with Fourier-transform infrared spectra, powder X-ray diffraction and thermogravimetric analysis of exposed LMOF powders confirm that bpee ligands are exchanged by amines and released inside the LMOF, triggering absorption and luminescence features which can be exploited for highly sensitive amine recognition. This principle was demonstrated in mixed matrix membranes (MMMs) prepared by a simple solvent-free method consisting of mixing Zn 2 (bpdc) 2 (bpee) with dimethylvinyl-terminated dimethylsiloxane and dimethylhydrogen siloxane. This method enabled the production of free-standing, permeable, and highly transparent MMMs which showed enormous potential and sensitivity to the detection of amines in gas phase and aqueous medium.

Viruses that infect bacteria (bacteriophages) are a promising alternative treatment for bacterial diseases, especially in the case of antibiotic resistance. Due to a renewed interest in phage therapies, development of rapid and specific detection methods for bacteria/bacteriophage interaction are gaining attention for proper diagnosis and treatment. This paper describes a new method to detect the interaction between Escherichia coli and bacteriophage T7 in a sensitive and quantitative way, using the nanomechanical motion of bacteria adhered to a cantilever surface. Our approach combines both deflection and dynamic frequency-domain characterization. The device was able to determine the viability of a low amount of living bacteria attached to the cantilever, and was used to monitor T7 interaction with E. coli over a wide range of virus concentrations up to 109 PFU ml-1. The nanomechanical assay described here requires no protein labeling and can be performed in a single reaction without additional reagents. The system was able to detect the interaction between a few thousand particles through the fluctuation of mechanical energy over a broad range of frequencies. The presented data provides the basis for more detailed studies of the sequence of molecular events that contribute to the motion of the device.

We study strong optical coupling of metal nanoparticle arrays with dielectric substrates. Based on the Fermi Golden Rule, the particle-substrate coupling is derived in terms of the photon absorption probability assuming a local dipole field. An increase in photocurrent gain is achieved through the optical coupling. In addition, we describe light-induced, mesoscopic electron dynamics via the nonlocal hydrodynamic theory of charges. At small nanoparticle size (<20 nm), the impact of this type of spatial dispersion becomes sizable. Both absorption and scattering cross sections of the nanoparticle are significantly increased through the contribution of additional nonlocal modes. We observe a splitting of local optical modes spanning several tenths of nanometers. This is a signature of semi-classical, strong optical coupling via the dynamic Stark effect, known as Autler-Townes splitting. The photocurrent generated in this description is increased by up to 2%, which agrees better with recent experiments than compared to identical classical setups with up to 6%. Both, the expressions derived for the particle-substrate coupling and the additional hydrodynamic equation for electrons are integrated into COMSOL for our simulations.

Two-dimensional arrays of hollow nanotubes made of TiO 2 are a promising platform for sensing, spectroscopy and light harvesting applications. Their straightforward fabrication via electrochemical anodization, growing nanotube pillars of finite length from a Ti foil, allows precise tailoring of geometry and, thus, material properties. We theoretically investigate these photonic crystal structures with respect to reduction of front surface reflection, achievable field enhancement, and photonic bands. Employing the Rigorous Coupled Wave Analysis (RCWA), we study the optical response of photonic crystals made of thin-walled nanotubes relative to their bare Ti foil substrate, including under additional charge carrier doping which might occur during the growth process.

miniSOG is the first flavin-binding protein that has been developed with the specific aim of serving as a genetically-encodable light-induced source of singlet oxygen ( 1 O 2 ). We have determined its 1.17 Å resolution structure, which has allowed us to investigate its mechanism of photosensitization using an integrated approach combining spectroscopic and structural methods. Our results provide a structural framework to explain the ability of miniSOG to produce 1 O 2 as a competition between oxygen- and protein quenching of its triplet state. In addition, a third excited-state decay pathway has been identified that is pivotal for the performance of miniSOG as 1 O 2 photosensitizer, namely the photo-induced transformation of flavin mononucleotide (FMN) into lumichrome, which increases the accessibility of oxygen to the flavin FMN chromophore and makes protein quenching less favourable. The combination of the two effects explains the increase in the 1 O 2 quantum yield by one order of magnitude upon exposure to blue light. Besides, we have identified several surface electron-rich residues that are progressively photo-oxidized, further contributing to facilitate the production of 1 O 2 . Our results help reconcile the apparent poor level of 1 O 2 generation by miniSOG and its excellent performance in correlative light and electron microscopy experiments.

We report on an organic electroluminescent device with simplified geometry and emission in the red to near infrared (NIR) spectral region which, has the lowest turn-on voltage value, 2.3 V, among light emitting electrochemical cells (LEECs). We have synthesized and characterized three novel ruthenium π-extended phenanthroimidazoles which differ on their N^N ligands. The use of dimethyl electron donating groups along with the π-extended phenanthroimidazole moiety promotes ambipolar transport thereby avoiding the use of additional charge transport layers. Furthermore, a facile cathode deposition method based on transfer of a molten alloy (Ga:In) on top of the active layer is deployed, thus avoiding high vacuum thermal deposition which adds versatile assets to our approach. We combine ambipolar charge transport organic complex design and a simple ambient cathode deposition to achieve a potentially cost effective red to NIR emitting device with outstanding performance, opening new avenues towards the development of simplified light emitting sources through device optimization.

We demonstrate that the direct application of numerical packets like Comsol to plasmonic effect in solar cells metallically modified in nano-scale may be strongly inaccurate if quantum corrections are neglected. The near-field coupling of surface plasmons in metallic nanoparticles deposited on the top of a solar cell with band electrons in a semiconductor substrate strongly enhances the damping of plasmons in metallic components, which is not accounted for in standard numerical packets using the Drude type dielectric function for metal (taken from measurements in bulk or in thin layers) as the prerequisite for the numerical e-m field calculus. Inclusion of the proper corrections to plasmon damping causes additional enhancement of the plasmon-induced photo-effect efficiency growth of a metalized photo-diode by ten percent, at least, in comparison to only effect induced by the electric field concentration near metallic nanoparticles. This happens to be consistent with the experimental observations which cannot be explained by only local increases of the electrical field near the curvature of metallic nanoparticles determined by a finite-element solution of the Maxwell⁻Fresnel boundary problem as given by a numerical system like Comsol. The proper damping rate for plasmons can be identified by application of the Fermi Golden Rule approach to the plasmon-band electron coupling. We demonstrate this effect including the material and size dependence in two types of solar cells, multi-crystalline Si and CIGS (copper-indium-gallium-diselenide) as idealized photo-diode semiconductor substrate modified by various metallic nano-particles, in comparison to the experimental data and Comsol simulation.

Nanoindentation with an atomic force microscope was used to investigate the mechanical properties of virus-like particles (VLPs) derived from the avian pathogen infectious bursal disease virus, in which the major capsid protein was modified by fusion with enhanced green fluorescent protein (EGFP). These VLPs assemble as ∼70-nm-diameter T = 13 icosahedral capsids with large cargo space. The effect of the insertion of heterologous proteins in the capsid was characterized in the elastic regime, revealing that EGFP-labeled chimeric VLPs are more rigid than unmodified VLPs. In addition, nanoindentation measurements beyond the elastic regime allowed the determination of brittleness and rupture force limit. EGFP incorporation results in a complex shape of the indentation curve and lower critical indentation depth of the capsid, rendering more brittle particles as compared to unlabeled VLPs. These observations suggest the presence of a complex and more constrained network of interactions between EGFP and the capsid inner shell. These results highlight the effect of fluorescent protein insertion on the mechanical properties of these capsids. Because the physical properties of the viral capsid are connected to viral infectivity and VLP transport and disassembly, our results are relevant to design improved labeling strategies for fluorescence tracking in living cells., (Copyright © 2018 Biophysical Society. Published by Elsevier Inc. All rights reserved.)

Antireflective transparent materials are essential for a myriad of applications to allow for clear vision and efficient light transmission. Despite the advances, efficient and low cost solutions to clean antireflective surfaces have remained elusive. Here, we present a practical approach that enables the production of antireflective polymer surfaces based on moth-eye inspired features incorporating photoinduced self-cleaning properties and enhanced mechanical resistance. The methodology involves the fabrication of sub-wavelength moth-eye nanofeatures onto transparent surface composite films in a combined processing step of nanoparticle coating and surface nanoimprinting. The resulting surfaces reduced the optical reflection losses from values of 9% of typical PMMA plastic films to an optimum value of 0.6% in the case of double-sided moth-eye nanoimprinted films. The composite moth-eye topography also showed an improved stiffness and scratch resistance. This technology represents a significant advancement not limited by scale, for the development of antireflective films for low cost application products.

Nanoparticles&mdash;regularly patterned or randomly dispersed&mdash;are a key ingredient for emerging technologies in photonics. Of particular interest are scattering and field enhancement effects of metal nanoparticles for energy harvesting and converting systems. An often neglected aspect in the modeling of nanoparticles are light interaction effects at the ultimate nanoscale beyond classical electrodynamics. Those arise from microscopic electron dynamics in confined systems, the accelerated motion in the plasmon oscillation and the quantum nature of the free electron gas in metals, such as Coulomb repulsion and electron diffusion. We give a detailed account on free electron phenomena in metal nanoparticles and discuss analytic expressions stemming from microscopic (Random Phase Approximation&mdash;RPA) and semi-classical (hydrodynamic) theories. These can be incorporated into standard computational schemes to produce more reliable results on the optical properties of metal nanoparticles. We combine these solutions into a single framework and study systematically their joint impact on isolated Au, Ag, and Al nanoparticles as well as dimer structures. The spectral position of the plasmon resonance and its broadening as well as local field enhancement show an intriguing dependence on the particle size due to the relevance of additional damping channels.

Nanotechnology provides a new design paradigm for alternative antibacterial strategies in the fight against drug-resistant bacteria. In this paper, the enhanced bactericidal action of moth-eye nanocomposite surfaces with a collaborative nanoparticle functional and topography structural mode of action is reported. The moth-eye nanocomposite surfaces are fabricated in combined processing steps of nanoparticle coating and surface nanoimprinting enabling the production of safer-by-design nanoparticle based antibacterial materials whereby the nanoparticle load is minimized whilst bactericidal efficiency is improved. The broad antibacterial activity of the nanocomposite moth-eye topographies is demonstrated against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli and Pseudomonas aeruginosa as model bacteria. The antibacterial performance of the moth-eye nanocomposite topographies is notably improved over that of the neat moth-eye surfaces with bacteria inhibition efficiencies up to 90%. Concurrently, the moth-eye nanocomposite topographies show a non-cytotoxic behaviour allowing for the normal attachment and proliferation of human keratinocytes., Competing Interests: The authors declare the following competing financial interests: the authors have applied for a patent on the topic of this paper., (This journal is © The Royal Society of Chemistry.)

We present the fabrication of TiO 2 nanotube electrodes with high biocompatibility and extraordinary spectroscopic properties. Intense surface-enhanced resonance Raman signals of the heme unit of the redox enzyme Cytochrome b 5 were observed upon covalent immobilization of the protein matrix on the TiO 2 surface, revealing overall preserved structural integrity and redox behavior. The enhancement factor could be rationally controlled by varying the electrode annealing temperature, reaching a record maximum value of over 70 at 475 °C. For the first time, such high values are reported for non-directly surface-interacting probes, for which the involvement of charge-transfer processes in signal amplification can be excluded. The origin of the surface enhancement is exclusively attributed to enhanced localized electric fields resulting from the specific optical properties of the nanotubular geometry of the electrode., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Spatial interaction effects between charge carriers in ionic systems play a sizable role beyond a classical Maxwellian description. We develop a nonlocal, two-fluid, hydrodynamic theory of charges and study ionic plasmon effects, i.e. collective charge oscillations in electrolytes. Ionic spatial dispersion arises from both positive and negative charge dynamics with an impact in the (far-)infrared. Despite highly classical parameters, nonlocal quenching of up to 90% is observed for particle sizes spanning orders of magnitude. Notably, the ionic system is widely tunable via ion concentration, mass and charge, in contrast to solid metal nanoparticles. A nonlocal soft plasmonic theory for ions is relevant for biological and chemical systems bridging hard and soft matter theory and allowing the investigation of non-classical effects in electrolytes in full analogy to solid metal particles. The presented semi-classical approach allows studying plasmonic photo-catalysis introducing nonlocal aspects into electrolyte-metal interactions.

The rapid emergence of antibiotic resistant bacteria has prompted the need for radically different approaches to combat bacterial infections. Among these, bioinspired surface topographies have emerged as an effective sustainable strategy to deter bacterial infection. This study demonstrates the bactericidal activity and cytocompatibility of the moth-eye mimetic topography produced by thermal polymer nanoimprinting. The moth-eye topography was found to have bactericidal capabilities against Gram negative and Gram positive bacteria. Electron microscopy imaging revealed the bactericidal effect caused by mechanical rupture of the bacteria wall inflicted by the topography on the adhered cells. The cytocompatibility of the surfaces was evidenced by assessing the proliferation and morphology of keratinocytes cultured on the nanotopography. The technology meets important needs in medical implant technology for materials that not only have good biocompatibility but also antibacterial properties for reducing the risk of infections and related health complications.

A novel technique for the creation of metal-organic framework (MOF) films based on soft-imprinting and their use as gas sensors was developed. The microporous MOF material [Zn₂(bpdc)₂(bpee)] (bpdc = 4,4'-biphenyldicarboxylate; bpee = 1,2-bipyridylethene) was synthesized solvothermally and activated by removing the occluded solvent molecules from its inner channels. MOF particles were characterized by powder X-ray diffraction and fluorescence spectroscopy, showing high crystallinity and intense photoluminescence. Scanning electron microscope images revealed that MOF crystals were mainly in the form of microneedles with a high surface-to-volume ratio, which together with the high porosity of the material enhances its interaction with gas molecules. MOF crystals were soft-imprinted into cellulose acetate (CA) films on quartz at different pressures. Atomic force microscope images of soft-imprinted films showed that MOF crystals were partially embedded into the CA. With this procedure, mechanically stable films were created, with crystals protruding from the CA surface and therefore available for incoming gas molecules. The sensing properties of the films were assessed by exposing them to saturated atmospheres of 2,4-dinitrotoluene, which resulted in a substantial quenching of the fluorescence after few seconds. The soft-imprinted MOF films on CA/quartz exhibit good sensing capabilities for the detection of nitroaromatics, which was attributed to the MOF sensitivity and to the novel and more efficient film processing method based on soft-imprinting., Competing Interests: The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

The combination of complementary techniques to characterize materials at the nanoscale is crucial to gain a more complete picture of their structure, a key step to design and fabricate new materials with improved properties and diverse functions. Here it is shown that correlative atomic force microscopy (AFM) and localization-based super-resolution microscopy is a useful tool that provides insight into the structure and emissive properties of fluorescent β-lactoglobulin (βLG) amyloid-like fibrils. These hybrid materials are made by functionalization of βLG with organic fluorophores and quantum dots, the latter being relevant for the production of 1D inorganic nanostructures templated by self-assembling peptides. Simultaneous functionalization of βLG fibers by QD655 and QD525 allows for correlative AFM and two-color super-resolution fluorescence imaging of these hybrid materials. These experiments allow the combination of information about the topography and number of filaments that compose a fibril, as well as the emissive properties and nanoscale spatial distribution of the attached fluorophores. This study represents an important step forward in the characterization of multifunctionalized hybrid materials, a key challenge in nanoscience., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This paper presents a multifunctional polymer surface that provides superhydrophobicity and self-cleaning functions together with an enhancement in mechanical and electrical performance. These functionalities are produced by nanoimprinting high aspect ratio pillar arrays on polymeric matrix incorporating functional reinforcing elements. Two distinct matrix-filler systems are investigated specifically, Carbon Nanotube reinforced Polystyrene (CNT-PS) and Reduced Graphene Oxide reinforced Polyvinylidene Difluoride (RGO-PVDF). Mechanical characterization of the topographies by quantitative nanoindentation and nanoscratch tests are performed to evidence a considerable increase in stiffness, Young's modulus and critical failure load with respect to the pristine polymers. The improvement on the mechanical properties is rationalized in terms of effective dispersion and penetration of the fillers into the imprinted structures as determined by confocal Raman and SEM studies. In addition, an increase in the degree of crystallization for the PVDF-RGO imprinted nanocomposite possibly accounts for the larger enhancement observed. Improvement of the mechanical ruggedness of functional textured surfaces with appropriate fillers will enable the implementation of multifunctional nanotextured materials in real applications.

Fluorescence imaging studies of the processes leading to photodynamic inactivation of bacteria have been limited due to the small size of microorganisms as well as by the faint fluorescence of most photosensitizers. A versatile method based on highly-sensitive fluorescence microscopy is presented which allows to study, in real time, the incorporation of photosensitizers inside S. aureus upon photodynamic action. The method takes advantage of the fluorescence enhancement of phenothiazine and porphyrin photosensitizers upon entering the bacterial cytosol after the cell wall has been compromised. In combination with typical assays, such as the addition of specific enhancers of reactive oxygen species, it is possible to extract mechanistic information about the pathway of photodynamic damage at the single-cell level. Imaging experiments in deuterated buffer strongly support a Type-I mechanism for methylene blue and a very minor role of singlet oxygen., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Controlling the stick-slip friction phenomenon is of major importance for many familiar situations. This effect originates from the periodic rupture of junctions created between two rubbing surfaces due to the increasing shear stress at the interface. It is ultimately responsible for the behavior of many braking systems, earthquakes, and unpleasant squeaky sounds caused by the scratching of two surfaces. In the case of a musical bow-stringed instrument, stick-slip is controlled in order to provide well-tuned notes at different intensities. A trained ear is able to distinguish slight sound variations caused by small friction differences. Hence, a violin can be regarded as a perfect benchmark to explore the stick-slip effect at the mesoscale. Two violin bow hairs were studied, a natural horse tail used in a professional philharmonic orchestra, and a synthetic one used with a violin for beginners. Atomic force microscopy characterization revealed clear differences when comparing the surfaces of both bow hairs, suggesting that a structure having peaks and a roughness similar to that of the string to which both bow hairs rubbed permits a better control of the stick-slip phenomenon.

Recent advances in imaging tools have greatly improved our ability to analyze the structure and molecular components of a wide range of biological systems at the nanoscale. High resolution imaging can be performed with a handful of techniques, each of them revealing particular features of the sample. A more comprehensive picture of a biological system can be achieved by combining the information provided by complementary imaging methods. Specifically, the correlation between super-resolution fluorescence imaging and atomic force microscopy (AFM) provides high resolution topography as well as specific chemical information, the latter with a spatial resolution that approaches that of AFM. We present a detailed protocol and discuss the requirements and challenges in terms of sample preparation, instrumentation, and image alignment to combine these two powerful techniques. This hybrid nanoscale imaging tool has the potential to provide robust validation for super-resolution methods as well as new insight into biological samples.

The fabrication of all polymer optical waveguides, based on a highly fluorescent conjugated polymer (CP) poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) and a mechanically flexible and biodegradable polymer, cellulose acetate (CA), is reported. The replication by hot embossing of patterned surfaces in CA substrates, onto which high quality F8BT films can be easily processed by spin coating, is exploited to produce an entirely plastic device that exhibits low optical loss and low threshold for amplified spontaneous emission (ASE). As a result, highly transparent and flexible waveguides are obtained, with excellent optical properties that remain unaltered after bending, allowing them to be adapted in various flexible photonic devices.

Correction for 'Assessing the potential of photosensitizing flavoproteins as tags for correlative microscopy' by Alberto Rodríguez-Pulido et al., Chem. Commun., 2016, 52, 8405-8408.

Photosensitizing flavoproteins have great potential as tags for correlative light and electron microscopy (CLEM). We examine the photostability of miniSOG mutants and their ability to photo-oxidize diaminobenzidine, both key aspects for CLEM. Our experiments reveal a complex relation between these parameters and the production of different reactive oxygen species.

Hybrid microscopy: A correlative microscopy tool that combines in situ super-resolution fluorescence microscopy based on single-molecule localization and atomic force microscopy is presented. Direct comparison with high- resolution topography allows the authors to improve fluorescence labeling and image analysis in super-resolution imaging., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Super-resolution fluorescence microscopy is ideally suited to study the complex organization of cell DNA in the 10-100 nm range. Novel methods to image directly labelled DNA, instead of DNA-associated proteins, are being developed and refined. This minireview provides an update of recent progress in super-resolution fluorescence imaging methods for DNA. These developments should allow a deeper understanding of chromatin structure and widen the scope of biological processes that may be investigated with super-resolution fluorescence microscopy., (© 2013 The Author Journal of Microscopy © 2013 Royal Microscopical Society.)