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Abstract In situ electrochemistry on micron and submicron-sized individual particles and thin layers is a valuable, emerging tool for process understanding and optimization in a variety of scientific and technological fields such as material science, process technology, analytical chemistry, and environmental sciences. Electrochemical characterization and manipulation coupled with soft X-ray spectromicroscopy helps identify, quantify, and optimize processes in complex systems such as those with high heterogeneity in the spatial and/or temporal domain. Here we present a novel platform optimized for in situ electrochemistry with variable liquid electrolyte flow in soft X-ray scanning transmission X-ray microscopes (STXM). With four channels for fluid control and a modular design, it is suited for a wealth of experimental conditions. We demonstrate its capabilities by proving the reversible oxidation and reduction of individual microbial biofilm structures formed by microaerophilic Fe(II)-oxidizing bacteria, also known as twisted stalks. We show spectromicroscopically the heterogeneity of the redox activity on the submicron scale. Examples are also provided of electrochemical modification of liquid electrolyte species (Fe(II) and Fe(III) cyanides), and in situ studies of electrodeposited copper nanoparticles as CO2 reduction electrocatalysts under reaction conditions.

Abstract Due to the abundance of microplastics in the environment, research about its possible adverse effects is increasing exponentially. Most studies investigating the effect of microplastics on cells still rely on commercially available polystyrene microspheres. However, the choice of these model microplastic particles can affect the outcome of the studies, as even nominally identical model microplastics may interact differently with cells due to different surface properties such as the surface charge. Here, we show that nominally identical polystyrene microspheres from eight different manufacturers significantly differ in their ζ-potential, which is the electrical potential of a particle in a medium at its slipping plane. The ζ-potential of the polystyrene particles is additionally altered after environmental exposure. We developed a microfluidic microscopy platform to demonstrate that the ζ-potential determines particle-cell adhesion strength. Furthermore, we find that due to this effect, the ζ-potential also strongly determines the internalization of the microplastic particles into cells. Therefore, the ζ-potential can act as a proxy of microplastic-cell interactions and may govern adverse effects reported in various organisms exposed to microplastics.

Abstract Aquatic environmental microbial biofilms grow in a broad range of redox environments from oxic to methanogenic, and they often also establish internal redox gradients. In technical applications, biofilms are also subjected to controlled redox conditions. Studies on biofilms often make use of fluorescence microscopic imaging techniques together with lectin binding analysis to gain insights into structure, composition, and functions of the biofilms. Here we studied the direct influence of redox potentials on fluorescence lectin binding analyses (FLBA) for two commonly used lectin-fluorophore conjugates. An effect of the electrical potential on signal intensity was observed and found to be statistically significant. The signal intensity changes however, remained within the range of a few percent total. A significant drop in intensity was only observed for extremely oxidizing potentials, typically not found under environmental conditions. Our results showed that the fluorophore itself and not the lectin binding to the respective glycoconjugate causes fluorescence changes. The two tested lectin-fluorophores are shown to be suitable for studying the distribution and composition of EPS in environmental biofilms or technical applications and under varying redox conditions.

Abstract Rice cultivation requires high amounts of phosphorus (P). However, significant amounts of P fertilizer additions may be retained by iron (Fe) oxides and are thus unavailable for plants. At the same time, rice cultivation has a high demand for silicic acid (Si), reducing Si availability after short duration of rice cultivation. By studying a paddy chronosequence with rice cultivation up to 2000 years, we show that Si limitation, observed as early as a few decades of rice cultivation, is limiting P availability along the paddy soils chronosequence. Using near edge X-ray absorption fine structure spectroscopy (NEXAFS) in a scanning transmission (soft) X-ray microscope (STXM) we show release of available P was linked to a Si-induced change in speciation of Fe-phases in soil particles and competition of Si with P for binding sites. Hence, low Si availability is limiting P availability in paddy soils. We propose that proper management of Si availability is a promising tool to improve the P supply of paddy plants.

Abstract Microplastic (MP) is a pervasive pollutant in nature that is colonised by diverse groups of microbes, including potentially pathogenic species. Fungi have been largely neglected in this context, despite their affinity for plastics and their impact as pathogens. To unravel the role of MP as a carrier of fungal pathogens in terrestrial ecosystems and the immediate human environment, epiplastic mycobiomes from municipal plastic waste from Kenya were deciphered using ITS metabarcoding as well as a comprehensive meta-analysis, and visualised via scanning electron as well as confocal laser scanning microscopy. Metagenomic and microscopic findings provided complementary evidence that the terrestrial plastisphere is a suitable ecological niche for a variety of fungal organisms, including important animal and plant pathogens, which formed the plastisphere core mycobiome. We show that MPs serve as selective artificial microhabitats that not only attract distinct fungal communities, but also accumulate certain opportunistic human pathogens, such as cryptococcal and Phoma-like species. Therefore, MP must be regarded a persistent reservoir and potential vector for fungal pathogens in soil environments. Given the increasing amount of plastic waste in terrestrial ecosystems worldwide, this interrelation may have severe consequences for the trans-kingdom and multi-organismal epidemiology of fungal infections on a global scale.

Biochar promotes plant growth via a slow release of nutrients; however, a mechanistic understanding of nutrient storage in biochar is lacking. Here, using high-resolution spectromicroscopy and mass spectrometry, the authors identify an organic coating on co-composted particles that enhances nutrient retention.

A method for the solvent-free photocatalytic conversion of solid and liquid substrates was developed, using a novel rod mill apparatus. In this setup, thin liquid films are realized which is crucial for an effective photocatalytic conversion due to the low penetration depth of light in heterogeneous systems. Several benzylic alcohols were oxidized with riboflavin tetraacetate as photocatalyst under blue light irradiation of the reaction mixture. The corresponding carbonyl compounds were obtained in moderate to good yields.

This article describes the state-of-the-art in 2D and 3D tomographic mid-IR imaging and its current and potential applications in the imaging of material and biological systems with a focus on cells and tissues. 2D FTIR microscopy is first presented in terms of the basic experimental configurations of the technique, optics, data and image acquisition. This first section provides a basis for the ensuing discussion on 3D FTIR spectro-microtomography. In the second part, examples of 2D and 3D chemical imaging are given with a focus on the use of molecular chemical probes and probe-free applications, respectively.

We present ScatterJn, an ImageJ (and Fiji) plugin for scatterplot-based exploration and analysis of analytical microscopy data. In contrast to commonly used scatterplot tools, it handles more than two input images (or image stacks, respectively) by creating a matrix of pairwise scatterplots. The tool offers the possibility to manually classify pixels by selecting regions of datapoints in the scatterplots as well as in the spatial domain. We demonstrate its functioning using a set of elemental maps acquired by SEM-EDX mapping of a soil sample. The plugin is available at https://savannah.nongnu.org/projects/scatterjn.