NanoSIMS Research Articles

Water Enhancement of Si Self‐Diffusion in Wadsleyite

AbstractWe investigated the H2O‐content dependence of Si self‐diffusion coefficient in Fe‐free wadsleyite using multi‐anvil experiments at pressures of 19–20 GPa, temperatures of 1573–1873 K, and H2O‐content ranging from ∼10 to 5,300 wt. ppm by the isotopic thin‐film diffusion‐couple method. The 29Si‐doped diffusion profiles were measured by nanoscale secondary ion mass spectrometry in the depth profiling mode. The H2O contents in the samples were analyzed by Fourier transformation infrared spectroscopy. The experimental results show a H2O enhancement of Si diffusion coefficient with a H2O content exponent of 0.8 ± 0.1. The activation enthalpy was found to be 270 ± 40 kJ/mol. The diffusion coefficients in the [100], [010], and [001] directions are indistinguishable. The temperature and H2O‐content dependences of Si diffusion indicate that H2O incorporation dramatically reduces the rheological strength of wadsleyite, whereas temperature has a relatively small effect. The viscosity in the mantle transition zone could be significantly reduced by H2O incorporation in wadsleyite. The viscosity contrast between mantle plumes and surroundings may control the evolution of plume shapes at 410–660 km depths.

NanoSIMS Imaging Reveals the Impact of Ligand-ASO Conjugate Stability on ASO Subcellular Distribution.

The delivery of antisense oligonucleotides (ASOs) to specific cell types via targeted endocytosis is challenging due to the low cell surface expression of target receptors and inefficient escape of ASOs from the endosomal pathway. Conjugating ASOs to glucagon-like peptide 1 (GLP1) leads to efficient target knockdown, specifically in pancreatic β-cells. It is presumed that ASOs dissociate from GLP1 intracellularly to enable an ASO interaction with its target RNA. It is unknown where or when this happens following GLP1-ASO binding to GLP1R and endocytosis. Here, we use correlative nanoscale secondary ion mass spectroscopy (NanoSIMS) and transmission electron microscopy to explore GLP1-ASO subcellular trafficking in GLP1R overexpressing HEK293 cells. We isotopically label both eGLP1 and ASO, which do not affect the eGLP1-ASO conjugate function. We found that the eGLP1 peptide and ASO are not detected at the same level in the same endosomes, within 30 min of GLP1R-HEK293 cell exposure to eGLP1-ASO. When we utilized different linker chemistry to stabilize the GLP1-ASO conjugate, we observed more ASO located with GLP1 compared to cell incubation with the less stable conjugate. Overall, our work suggests that the ASO separates from GLP1 relatively early in the endocytic pathway, and that linker chemistry might impact the GLP1-ASO function.

High spatial resolution imaging of subcellular macro and trace element distribution during phagocytosis.

The bioavailability of trace elements in the course of evolution had an essential influence on the emergence of life itself. This is reflected in the co-evolution between eukaryotes and prokaryotes. In this study, the influence and cellular distribution of bioelements during phagocytosis at the host-pathogen interface were investigated using high-resolution nanoscale secondary ion mass spectrometry (NanoSIMS) and quantitative inductively coupled plasma mass spectrometry. In the eukaryotic murine macrophages (RAW 264.7 cell line), the cellular Fe/Zn ratio was found to be balanced, whereas the dominance of iron in the prokaryotic cells of the pathogen Salmonella enterica Serovar Enteritidis was ∼90% compared to zinc. This confirms the evolutionary increased zinc requirement of the eukaryotic animal cell. Using NanoSIMS, the Cs+ primary ion source allowed high spatial resolution mapping of cell morphology down to the subcellular level. At a comparable resolution, several low-abundant trace elements could be mapped during phagocytosis with a RF plasma O- primary ion source. An enrichment of copper and nickel could be detected in the prokaryotic cells. Surprisingly, an accumulation of cobalt in the area of the nuclear envelope was observed, indicating an interesting but still unknown distribution of this trace element in murine macrophages.

Regulation strategy for nutrient-dependent carbon and nitrogen stoichiometric homeostasis in freshwater phytoplankton

Phytoplankton carbon (C) and nitrogen (N) stoichiometric homeostasis plays an important role in aquatic ecosystems. Their C:N ratio is a result of cellular metabolic balance, and the relevant regulatory strategy for its plasticity is still unclear. Therefore, a field survey of seven reservoirs in Tianjin, North China, was conducted to understand variations in phytoplankton C:N ratios, and a laboratory culture of Chlamydomonas reinhardtii was performed to understand the relevant regulation strategy for cellular C-N stoichiometric homeostasis under different C and N availability by using transcriptome sequencing and Nano SIMS and C stable isotope analyses. The results indicated that CO2 limitation had no significant effect on the phytoplankton C:N ratio in either scene, whereas limitation of dissolved inorganic N induced a 35% higher ratio in the field and a 138% higher ratio in the laboratory. Under CO2 limitation, algal CO2-concentrating mechanisms were operated to ensure a C supply, and coupled C-N molecular regulation remained the cellular C:N ratio stable. Under nitrate limitation, differentially expressed gene-regulated intensities increase enormously, and their increasing proportion was comparable to that of the algal C:N ratio; cellular metabolism was reorganized to form a “subhealthy” C-N stoichiometric state with high C:N ratios. In addition, the N transport system had a specific role under CO2 and nitrate limitations. Our study implies that algal stoichiometric homeostasis depends on the involved limitation element and will help to deepen the understanding of C-N stoichiometric homeostasis in freshwater phytoplankton.

Visualizing Mineral-Associated Organic Matters in Long-Term Fertilization Treated Soils by NanoSIMS and SR-FTIR

Formation of mineral-associated organic matters is essential for long-term soil organic carbon preservation. However, the regulation pathways of mineral-associated organic matters in soils remains largely undescribed, especially at the submicron scale. Using a well-controlled long-term (32 years) field experiment at the Jiangxi Institute of Red Soils, Jinxian, China, we showed that long-term manure fertilization significantly (P < 0.05) increased the available Al and Fe concentrations over one order of magnitude in soil water dispersible colloids compared to no fertilization and chemical fertilization. Nano-scale secondary ion mass spectrometry (NanoSIMS) images and region of interest (ROI) analysis provided direct evidence demonstrating that long-term manure fertilization increased the 27Al16O−/12C−, 27Al16O−/12C14N−, 56Fe16O−/12C−, and 56Fe16O−/12C14N− ratios compared to no fertilization and chemical fertilization. This finding revealed that long-term manure fertilization may potentially enhance the stability of organic carbon and nitrogen. Synchrotron radiation based FTIR spectromicroscopy further supported that secondary minerals (<950 cm−1) were co-localized with amines, lipids, and proteins in the long-term manure fertilization, but only co-localized with proteins in the no fertilization and chemical fertilization. To summarize, our findings highlight the importance of manure inputs in increasing formation of mineral-associated organic matters and thus potentially increasing soil carbon persistence.

Cryoturbation impacts iron-organic carbon associations along a permafrost soil chronosequence in northern Alaska

In permafrost soils, substantial amounts of organic carbon (OC) are potentially protected from microbial degradation and transformation into greenhouse gases by association with reactive iron (Fe) minerals. As permafrost environments respond to climate change, increased drainage of thaw lakes in permafrost regions is predicted. Soils will subsequently develop on these drained thaw lakes, but the role of Fe-OC associations in future OC stabilization during this predicted soil development is unknown. To fill this knowledge gap, we have examined Fe-OC associations in organic, cryoturbated and mineral horizons along a 5500-year chronosequence of drained thaw lake basins in Utqiaġvik, Alaska. By applying chemical extractions, we found that ∼17% of the total OC content in cryoturbated horizons is associated with reactive Fe minerals, compared to ∼10% in organic or mineral horizons. As soil development advances, the total stocks of Fe-associated OC more than double within the first 50 years after thaw lake drainage, because of increased storage of Fe-associated OC in cryoturbated horizons (from 8 to 75% of the total Fe-associated OC stock). Spatially-resolved nanoscale secondary ion mass spectrometry showed that OC is primarily associated with Fe(III) (oxyhydr)oxides which were identified by 57Fe Mössbauer spectroscopy as ferrihydrite. High OC:Fe mass ratios (>0.22) indicate that Fe-OC associations are formed via co-precipitation, chelation and aggregation. These results demonstrate that, given the proposed enhanced drainage of thaw lakes under climate change, OC is increasingly incorporated and stabilized by the association with reactive Fe minerals as a result of soil formation and increased cryoturbation.

River Organic Carbon Fluxes Modulated by Hydrodynamic Sorting of Particulate Organic Matter

AbstractRivers regulate the global carbon cycle by transferring particulate organic carbon (POC) from terrestrial landscapes to marine sedimentary basins, but the processes controlling the amount and composition of fluvially exported POC are poorly understood. We propose that hydrodynamic sorting processes modify POC fluxes during fluvial transit. We test this hypothesis by studying POC transported along a ∼1,200 km reach of the Rio Bermejo, Argentina. Nanoscale secondary ion mass spectrometry revealed that POC was either fine, mineral‐associated organic matter, or coarse discrete organic particles. Mineral‐associated POC is more resistant to oxidation and has a lower particle settling velocity than discrete POC. Consequently, hydraulic sorting and downstream fining amplify the proportion of fine, mineral‐associated POC from ∼55% to ∼78% over 1,220 km of downstream transit. This suggests that mineral‐associated POC has a greater probability of export and preservation in marine basins than plant detritus, which may be oxidized to CO2 during transit.

Comprehensive Speciation Analysis of Residual Gadolinium in Deep Cerebellar Nuclei in Rats Repeatedly Administered With Gadoterate Meglumine or Gadodiamide.

Several preclinical studies have reported the presence of gadolinium (Gd) in different chemical forms in the brain, depending on the class (macrocyclic versus linear) of Gd-based contrast agent (GBCA) administered. The aim of this study was to identify, with a special focus on insoluble species, the speciation of Gd retained in the deep cerebellar nuclei (DCN) of rats administered repeatedly with gadoterate or gadodiamide 4 months after the last injection. Three groups (N = 6/group) of healthy female Sprague-Dawley rats (SPF/OFA rats; Charles River, L'Arbresle, France) received a cumulated dose of 50 mmol/kg (4 daily intravenous administrations of 2.5 mmol/kg, for 5 weeks, corresponding to 80-fold the usual clinical dose if adjusted for man) of gadoterate meglumine (macrocyclic) or gadodiamide (linear) or isotonic saline for the control group (4 daily intravenous administrations of 5 mL/kg, for 5 weeks). The animals were sacrificed 4 months after the last injection. Deep cerebellar nuclei were dissected and stored at -80°C before sample preparation. To provide enough tissue for sample preparation and further analysis using multiple techniques, DCN from each group of 6 rats were pooled. Gadolinium species were extracted in 2 consecutive steps with water and urea solution. The total Gd concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS). Soluble Gd species were analyzed by size-exclusion chromatography coupled to ICP-MS. The insoluble Gd species were analyzed by single-particle (SP) ICP-MS, nanoscale secondary ion mass spectroscopy (NanoSIMS), and scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy (STEM-EDX) for elemental detection. The Gd concentrations in pooled DCN from animals treated with gadoterate or gadodiamide were 0.25 and 24.3 nmol/g, respectively. For gadoterate, the highest amount of Gd was found in the water-soluble fractions. It was present exclusively as low-molecular-weight compounds, most likely as the intact GBCA form. In the case of gadodiamide, the water-soluble fraction of DCN was composed of high-molecular-weight Gd species of approximately 440 kDa and contained only a tiny amount (less than 1%) of intact gadodiamide. Furthermore, the column recovery calculated for this fraction was incomplete, which suggested presence of labile complexes of dissociated Gd3+ with endogenous molecules. The highest amount of Gd was detected in the insoluble residue, which was demonstrated, by SP-ICP-MS, to be a particulate form of Gd. Two imaging techniques (NanoSIMS and STEM-EDX) allowed further characterization of these insoluble Gd species. Amorphous, spheroid structures of approximately 100-200 nm of sea urchin-like shape were detected. Furthermore, Gd was consistently colocalized with calcium, oxygen, and phosphorous, strongly suggesting the presence of structures composed of mixed Gd/Ca phosphates. No or occasional colocalization with iron and sulfur was observed. A dedicated analytical workflow produced original data on the speciation of Gd in DCN of rats repeatedly injected with GBCAs. The addition, in comparison with previous studies of Gd speciation in brain, of SP element detection and imaging techniques allowed a comprehensive speciation analysis approach. Whereas for gadoterate the main fraction of retained Gd was present as intact GBCA form in the soluble fractions, for linear gadodiamide, less than 10% of Gd could be solubilized and characterized using size-exclusion chromatography coupled to ICP-MS. The main Gd species detected in the soluble fractions were macromolecules of 440 kDa. One of them was speculated to be a Gd complex with iron-binding protein (ferritin). However, the major fraction of residual Gd was present as insoluble particulate species, very likely composed of mixed Gd/Ca phosphates. This comprehensive Gd speciation study provided important evidence for the dechelation of linear GBCAs and offered a deeper insight into the mechanisms of Gd deposition in the brain.

Tungsten distribution and vertical migration in soils near a typical abandoned tungsten smelter

As an emerging contaminant, tungsten’s distribution and speciation in soils are far from understood. In this study, two soil profiles near a typical abandoned tungsten smelter in Hunan Province, China were collected and investigated, to ascertain the binding and association of tungsten with different soil components and subsequently to understand its mobility. The data showed that past tungsten smelting activities resulted in elevated concentrations of both tungsten and arsenic in the soil profiles, both of which ranged from dozens of to a few hundred mg/kg. Nano-scale secondary ion mass spectrometry (NanoSIMS) was employed to quantify the distribution and association of tungsten with various other elements. Combined with sequential extraction and mineralogical analysis, the data from NanoSIMS showed that aluminosilicates including kaolinite and illite were the most important mineral hosts for tungsten, whereas arsenic was predominantly bound to iron (oxyhydr)oxides. Additional data from 13C nuclear magnetic resonance and X-ray photoelectron spectroscopy revealed that soil organic matter retained tungsten in deep soils (>70 cm) by binding tungsten through carboxyls on aromatic rings. Compared to arsenic, tungsten migrated deeper in the soil profiles, suggesting its higher mobility and potential risk to groundwater quality.

Multimodal Registration of Fish and Nanosims Images Using Convolutional Neural Network Models

Nanoscale secondary ion mass spectrometry (nanoSIMS) and fluorescence in situ hybridization (FISH) microscopy provide high-resolution, multimodal image representations of the identity and cell activity respectively of targeted microbial communities in microbiological research. Despite its importance to microbiologists, multimodal registration of FISH and nanoSIMS images is challenging given the morphological distortion and background noise in both images. In this study, we use convolutional neural networks (CNNs) for multiscale feature extraction, shape context for computation of the minimum transformation cost feature matching and the thin-plate spline (TPS) model for multimodal registration of the FISH and nanoSIMS images. Registration accuracy was quantitatively assessed against manually registered images, at both, the pixel and structural levels using standard metrics. Although all six tested CNN models performed well, ResNet18 was observed to outperform VGG16, VGG19, GoogLeNet and ShuffleNet and ResNet101 based on most metrics. This study demonstrates the utility of CNNs in the registration of multimodal images with significant background noise and morphology distortion. We also show aggregate shape, preserved by binarization, to be a robust feature for registering multimodal microbiology-related images.

Profiling the Regulation of Histone Methylation and Demethylation by Metabolites and Metals.

Here we describe how to profile the contribution of metabolism and implication of metals to histone methylation and demethylation. The techniques described with the adequate protocols are metabolomics, quantitative proteomics, inductively coupled mass spectrometry and nanoscale secondary ion mass spectrometry.

High spatial resolution and precision NanoSIMS for sulfur isotope analysis

The developed method can be used for analyzing the δ34S of pyrite samples with a limited analyzable region (>1 × 1 μm2) with high precision in nano-scale secondary ion mass spectroscopy.

Localization and Absolute Quantification of Dopamine in Discrete Intravesicular Compartments Using NanoSIMS Imaging.

The absolute concentration and the compartmentalization of analytes in cells and organelles are crucial parameters in the development of drugs and drug delivery systems, as well as in the fundamental understanding of many cellular processes. Nanoscale secondary ion mass spectrometry (NanoSIMS) imaging is a powerful technique which allows subcellular localization of chemical species with high spatial and mass resolution, and high sensitivity. In this study, we combined NanoSIMS imaging with spatial oversampling with transmission electron microscopy (TEM) imaging to discern the compartments (dense core and halo) of large dense core vesicles in a model cell line used to study exocytosis, and to localize 13C dopamine enrichment following 4–6 h of 150 μM 13C L-3,4-dihydroxyphenylalanine (L-DOPA) incubation. In addition, the absolute concentrations of 13C dopamine in distinct vesicle domains as well as in entire single vesicles were quantified and validated by comparison to electrochemical data. We found concentrations of 87.5 mM, 16.0 mM and 39.5 mM for the dense core, halo and the whole vesicle, respectively. This approach adds to the potential of using combined TEM and NanoSIMS imaging to perform absolute quantification and directly measure the individual contents of nanometer-scale organelles.

Analysis of impurity doping in tunnel junction grown on core–shell structure composed of GaInN/GaN multiple-quantum-shells and GaN nanowire

This study aimed to investigate and analyze the impurity doping characteristics in tunnel junctions (TJs) grown on core–shell structures, comprising GaInN/GaN multiple-quantum-shells (MQSs) and GaN nanowires. To this end, the impurity, structural, and electrical properties of the samples were characterized by scanning electron microscopy, scanning transmission electron microscopy, atom probe tomography (APT), nanoscale secondary ion mass spectrometry (NanoSIMS), and electroluminescence of the device which was fabricated for a prototype laser device to demonstrate an electrical operation of the MQSs layer. From the experimental results of NanoSIMS and APT, we demonstrated that the Mg-related problems in the TJ, such as the diffusion to the n++-GaN layer from the p+-GaN layer and formation of clusters in p+-GaN, are critical. Consequently, they cause a high operating voltage and dot-like spot emission of the light-emitting device. Based on the analysis, we suggested remedies and strategies to further improve the TJs that work well.

Calculation and Interpretation of Substrate Assimilation Rates in Microbial Cells Based on Isotopic Composition Data Obtained by nanoSIMS

Stable isotope probing (SIP) combined with nano-scale secondary ion mass spectrometry (nanoSIMS) is a powerful approach to quantify assimilation rates of elements such as C and N into individual microbial cells. Here, we use mathematical modeling to investigate how the derived rate estimates depend on the model used to describe substrate assimilation by a cell during a SIP incubation. We show that the most commonly used model, which is based on the simplifying assumptions of linearly increasing biomass of individual cells over time and no cell division, can yield underestimated assimilation rates when compared to rates derived from a model that accounts for cell division. This difference occurs because the isotopic labeling of a dividing cell increases more rapidly over time compared to a non-dividing cell and becomes more pronounced as the labeling increases above a threshold value that depends on the cell cycle stage of the measured cell. Based on the modeling results, we present formulae for estimating assimilation rates in cells and discuss their underlying assumptions, conditions of applicability, and implications for the interpretation of intercellular variability in assimilation rates derived from nanoSIMS data, including the impacts of storage inclusion metabolism. We offer the formulae as a Matlab script to facilitate rapid data evaluation by nanoSIMS users.

Dextran-based matrix functionalization to promote WJ-MSCs amplification: synthesis and characterization

Several clinical studies have reported the benefit of the administration of Mesenchymal Stem Cells (MSCs) in cell therapies. However, their routine applications need new substrates to amplify MSCs in vitro according to Good Manufacturing Practices (GMP) conditions and microcarriers are particularly suited for these purposes. In order to optimize the surface properties of Cytodex I microcarriers (Cyt), poly N-isopropylacrylamide (pNIPAM) has been grafted on their surface to promote MSCs adhesion, proliferation, but also to control their detachment by a decrease in temperature. The polymer coating generated on the microcarriers was analyzed using Time-of-Flight, Nanoscale Secondary Ion Mass Spectrometry, and Atomic Force Microscopy. We have confirmed the success of the pNIPAM grafting on Cyt with a two-steps reaction and correlated the influence on matrix functionalization in the function of the organic solvent used to disperse the microcarriers. The effects of pNIPAM functionalization have been explored on Wharton’s jelly-MSCs (WJ-MSCs) culture and cell thermal detachment was monitored with fluorescent microscopy. The in vitro results have indicated that WJ-MSCs have a better growth on Cyt-pNIPAM. However, pNIPAM thermal cell detachment was lower than trypsinization, implying that the minimum effective molecular weight and surface density of polymer chains have still to be future optimized.

Functional complexity explains the depth-dependent response of organic matter to liming at the nanometer scale

The development of effective strategies to maintain/increase soil C is hindered by the poor process-level understanding of the impact of management practices on C preservation, particularly at different soil depths. Based on the distinct biogeochemistry existing across a soil profile, a depth-dependent response of organic matter (OM) to soil amendments was hypothesized. To test this, we investigated the effect on OM preservation of lime addition to the topsoil and the subsoil of a volcanic soil classified as Andosol – the mineral soil with the largest organic C content worldwide. We incubated samples from each soil layer with (or without) lime addition, in the presence or absence of 13C- and 15N-labeled plant residue (simulating plant C inputs to the soil). The fate of OM in bulk soil and OM-mineral associations of microaggregates was measured using conventional chemical analyses and nano-scale secondary ion mass spectrometry, respectively. The results revealed contrasting geochemical properties existing within the soil profile, i.e. pH and amount of allophane increasing with soil depth. Functional complexity of OM also increased with depth, as revealed by an increase in spatial and molecular heterogeneity of OM, i.e. a larger proportion of microbial-derived OM with high spatial separation found in the subsoil. Lime addition caused OM destabilization as denoted by the increase in the amount of water-extractable C in both the topsoil and the subsoil (P < 0.05). In the topsoil, OM coverage of mineral surfaces decreased with liming from 49% to 30% whereas the opposite was observed in the subsoil, where it increased from 23% to 29%. Thus, liming caused the disruption of OM-mineral associations within microaggregates in the topsoil, but not in the subsoil. We infer that, at depth, the OM destabilization involved the mobilization of OM previously protected within macroaggregates. This pulse of labile C generated an advantageous environment for microbial OM mineralization in the subsoil, but this effect was diluted in the topsoil, richer in OM and where OM functional complexity is smaller. Depth-dependent soil geochemical properties and functional complexity determine differences in the effect of liming on the fate of soil OM in top vs. subsoils.

Metabolic history and metabolic fitness as drivers of anabolic heterogeneity in isogenic microbial populations

Microbial populations often display different degrees of heterogeneity in their substrate assimilation, that is, anabolic heterogeneity. It has been shown that nutrient limitations are a relevant trigger for this behaviour. Here we explore the dynamics of anabolic heterogeneity under nutrient replete conditions. We applied time-resolved stable isotope probing and nanoscale secondary ion mass spectrometry to quantify substrate assimilation by individual cells of Pseudomonas putida, P. stutzeri and Thauera aromatica. Acetate and benzoate at different concentrations were used as substrates. Anabolic heterogeneity was quantified by the cumulative differentiation tendency index. We observed two major, opposing trends of anabolic heterogeneity over time. Most often, microbial populations started as highly heterogeneous, with heterogeneity decreasing by various degrees over time. The second, less frequently observed trend, saw microbial populations starting at low or very low heterogeneity, and remaining largely stable over time. We explain these trends as an interplay of metabolic history (e.g. former growth substrate or other nutrient limitations) and metabolic fitness (i.e. the fine-tuning of metabolic pathways to process a defined growth substrate). Our results offer a new viewpoint on the intra-population functional diversification often encountered in the environment, and suggests that some microbial populations may be intrinsically heterogeneous.

Development of Mercury Analysis by NanoSIMS for the Localization of Mercury-Selenium Particles in Whale Liver.

Nanoscale secondary ion mass spectrometry (NanoSIMS) is a dynamic SIMS technique, which offers high spatial resolution allowing the mapping of chemical elements at the nanometer scale combined with high sensitivity. However, SIMS for mercury analysis is a challenging issue due to the low secondary ion yield and has never been done on NanoSIMS. The introduction of an rf plasma oxygen primary ion source on NanoSIMS enabled higher lateral resolution and higher sensitivity for electropositive elements such as most metals. In this paper, for the first time, mercury analysis by NanoSIMS was developed applying the new rf plasma O- ion source. All mercury isotopes could be detected as Hg+ secondary ions and the isotopic pattern corresponded to their natural isotopic abundances. Furthermore, Hg+ detection in HgSe nanocrystals has been investigated where polyatomic interferences from selenium clusters were identified and separated by high mass resolution (ΔM/M ≥ 3200). However, in the presence of selenium a strong matrix effect was observed, decreasing the Hg+ secondary ion yield. In addition, a detection of Se+ ions was possible, too. The newly developed method was successfully applied to nanoscale localization by chemical imaging of HgSe particles accumulated in the liver tissue of sperm whale (Physeter macrocephalus). This demonstrated the applicability of NanoSIMS not only for mercury detection in surface analysis but also for mercury mapping in biological samples.

Recently photoassimilated carbon and fungus-delivered nitrogen are spatially correlated in the ectomycorrhizal tissue of Fagus sylvatica.

Summary Ectomycorrhizal plants trade plant‐assimilated carbon for soil nutrients with their fungal partners. The underlying mechanisms, however, are not fully understood. Here we investigate the exchange of carbon for nitrogen in the ectomycorrhizal symbiosis of Fagus sylvatica across different spatial scales from the root system to the cellular level.We provided 15N‐labelled nitrogen to mycorrhizal hyphae associated with one half of the root system of young beech trees, while exposing plants to a 13CO2 atmosphere. We analysed the short‐term distribution of 13C and 15N in the root system with isotope‐ratio mass spectrometry, and at the cellular scale within a mycorrhizal root tip with nanoscale secondary ion mass spectrometry (NanoSIMS).At the root system scale, plants did not allocate more 13C to root parts that received more 15N. Nanoscale secondary ion mass spectrometry imaging, however, revealed a highly heterogenous, and spatially significantly correlated distribution of 13C and 15N at the cellular scale.Our results indicate that, on a coarse scale, plants do not allocate a larger proportion of photoassimilated C to root parts associated with N‐delivering ectomycorrhizal fungi. Within the ectomycorrhizal tissue, however, recently plant‐assimilated C and fungus‐delivered N were spatially strongly coupled. Here, NanoSIMS visualisation provides an initial insight into the regulation of ectomycorrhizal C and N exchange at the microscale.