Avoiding artefacts during electron microscopy of silver nanomaterials exposed to biological environments

ArtSeg-Artifact segmentation and removal in brightfield cell microscopy images without manual pixel-level annotations

Brightfield cell microscopy is a foundational tool in life sciences. The acquired images are prone to contain visual artifacts that hinder downstream analysis, and automatically removing them is therefore of great practical interest. Deep convolutional neural networks are state-of-the-art for image segmentation, but require pixel-level annotations, which are time-consuming to produce. Here, we propose ScoreCAM-U-Net, a pipeline to segment artifactual regions in brightfield images with limited user input. The model is trained using only image-level labels, so the process is faster by orders of magnitude compared to pixel-level annotation, but without substantially sacrificing the segmentation performance. We confirm that artifacts indeed exist with different shapes and sizes in three different brightfield microscopy image datasets, and distort downstream analyses such as nuclei segmentation, morphometry and fluorescence intensity quantification. We then demonstrate that our automated artifact removal ameliorates this problem. Such rapid cleaning of acquired images using the power of deep learning models is likely to become a standard step for all large scale microscopy experiments.

Localizing Proteins on Single Trafficking Organelles in 3D with Semisynthetic Gold Labeling and Platinum Replica Electron Microscopy

The three-dimensional structures of organelles can be visualized at high resolutions using electron microscopy and tomography. Combining genetically encoded tags with tomography enables the specific targeting and detection of identified proteins inside cells. Here, we describe a method for attaching metal-binding gold nanoparticles to proteins genetically tagged with hexa-histidine sequences. We apply this strategy to visualize the position of intracellular proteins on single organelles in unroofed cells with platinum replica electron microscopy at the nanoscale in three dimensions. We have found that this combined method can label and localize proteins with isotropic high precision to generate quantitative maps of protein positions in and around trafficking organelles at the inner plasma membrane of mammalian cells.

Endocytosed silver nanoparticles degrade in lysosomes to form secondary nanoparticle structures during expression of autophagy genes in osteogenic cells

Silver nanoparticles (AgNPs) are increasingly used in combination with biomaterials, such as bone grafts, to provide antimicrobial properties. Our research focused on the cytotoxic and intracellular uptake mechanism of AgNPs on osteogenic cells, and the affected gene expression of osteoblasts exposed to AgNPs. Osteoblast cells were found to be relatively resistant to AgNP exposure, compared to osteoclasts, with a higher IC₅₀ and fewer adverse morphological features. AgNPs were endocytosed within lysosomes, which resulted in the secondary internal formation of curved Ag^O nano-chains assemblies within the cytosol. Furthermore, osteoblasts demonstrated an oxidative stress response, with autophagic cell death mechanisms, as indicated from qRT²-PCR analysis, with sustained upregulation of the protective gene Heme Oxygenase 1 reaching 86-fold by 48 hours (10 μg/mL). The internalization and fate of AgNPs in osteogenic cells, and the resulting impact on gene expression over time provide further understanding of the nanotoxicity mechanism of AgNPs.

Spatially Resolved Dissolution and Speciation Changes of ZnO Nanorods during Short-Term in Situ Incubation in a Simulated Wastewater Environment

Zinc oxide engineered nanomaterials (ZnO ENMs) are used in a variety of applications worldwide due to their optoelectronic and antibacterial properties with potential contaminant risk to the environment following their disposal. One of the main potential pathways for ZnO nanomaterials to reach the environment is via urban wastewater treatment plants. So far there is no technique that can provide spatiotemporal nanoscale information about the rates and mechanisms by which the individual nanoparticles transform. Fundamental knowledge of how the surface chemistry of individual particles change, and the heterogeneity of transformations within the system, will reveal the critical physicochemical properties determining environmental damage and deactivation. We applied a methodology based on spatially resolved in situ X-ray fluorescence microscopy (XFM), allowing observation of real-time dissolution and morphological and chemical evolution of synthetic template-grown ZnO nanorods (∼725 nm length, ∼140 nm diameter). Core-shell ZnO-ZnS nanostructures were formed rapidly within 1 h, and significant amounts of ZnS species were generated, with a corresponding depletion of ZnO after 3 h. Diffuse nanoparticles of ZnS, Zn₃(PO₄)₂, and Zn adsorbed to Fe-oxyhydroxides were also imaged in some nonsterically impeded regions after 3 h. The formation of diffuse nanoparticles was affected by ongoing ZnO dissolution (quantified by inductively coupled plasma mass spectrometry) and the humic acid content in the simulated sludge. Complementary ex situ X-ray absorption spectroscopy and scanning electron microscopy confirmed a significant decrease in the ZnO contribution over time. Application of time-resolved XFM enables predictions about the rates at which ZnO nanomaterials transform during their first stages of the wastewater treatment process.

Interactions and effects of metal oxide nanoparticles on microorganisms involved in biological wastewater treatment

To clarify the toxicological effects of metal oxide nanoparticles (NPs) on microorganisms with environmental relevance, it is necessary to understand their interactions. In this work, they were studied the effects and the morphological interactions of two metal oxide NPs (ZnO and TiO₂ ) with microorganisms, during aerobic treatment of wastewater. The effects were evaluated according to nutrient removal from wastewater, while morphological interactions were determined by three different techniques such as TEM, HAADF-STEM, as well as an elemental mapping. According to results about effects of both NPs, they inhibited the removal of organic matter and ammonia nitrogen, and enhanced the orthophosphate removal. Related to morphological interactions, the electron-dense material of both NPs was mainly observed bounded to cell membrane. In tests with ZnO NPs, it was also observed electron-dense material internalized in microorganisms without physical damage in cell membrane. The elemental mapping was useful to determine that the electron-dense material corresponded to Zn and Ti. Both interactions, internalization and attachment of NPs on cell membrane of microorganisms may trigger the negative effect in the removal of organic matter and nitrogen.

Silver nanoparticles reduce brain inflammation and related neurotoxicity through induction of H2S-synthesizing enzymes

Silver nanoparticles (AgNP) are known to penetrate into the brain and cause neuronal death. However, there is a paucity in studies examining the effect of AgNP on the resident immune cells of the brain, microglia. Given microglia are implicated in neurodegenerative disorders such as Parkinson's disease (PD), it is important to examine how AgNPs affect microglial inflammation to fully assess AgNP neurotoxicity. In addition, understanding AgNP processing by microglia will allow better prediction of their long term bioreactivity. In the present study, the in vitro uptake and intracellular transformation of citrate-capped AgNPs by microglia, as well as their effects on microglial inflammation and related neurotoxicity were examined. Analytical microscopy demonstrated internalization and dissolution of AgNPs within microglia and formation of non-reactive silver sulphide (Ag2S) on the surface of AgNPs. Furthermore, AgNP-treatment up-regulated microglial expression of the hydrogen sulphide (H2S)-synthesizing enzyme cystathionine-γ-lyase (CSE). In addition, AgNPs showed significant anti-inflammatory effects, reducing lipopolysaccharide (LPS)-stimulated ROS, nitric oxide and TNFα production, which translated into reduced microglial toxicity towards dopaminergic neurons. Hence, the present results indicate that intracellular Ag2S formation, resulting from CSE-mediated H2S production in microglia, sequesters Ag+ ions released from AgNPs, significantly limiting their toxicity, concomitantly reducing microglial inflammation and related neurotoxicity.

Biosensing breast cancer cells based on a three-dimensional TIO2 nanomembrane transducer

The early diagnosis of breast cancer is crucial for the successful treatment and recovery phases of the patients suffering from the disease. Although mammography is considered the gold standard for diagnosis, it fails to detect some cancers in high-density breasts. In this work, we propose for the first time a tridimensional biosensor platform, to be used on an electrochemical point-of-care device. The bioconjugated platform is constructed on a series of covalent linkages between lectin molecules and a cysteine layer immobilized over gold-coated TiO₂ butterfly-like tridimensional nanomembranes. Through the use of vegetal lectins, we managed to take advantage of the markedly atypical glycomic profile of the cancerous mammalian cell membrane and successfully made a distinction between highly invasive (T47D) and less invasive (MCF7) cancer cell lines. The selectivity of the biosensor was tested by using normal human skin-fibroblast. The proposed cytosensor demonstrated limits of detection as low as 10 cells mL^-1 for every cell line and a linear range from 10 to 1.0×10⁶ cells mL^-1. Considering that electrochemical impedance values can be correlated with the number of breast cancer cells present in the sample, we suggest that the proposed platform could be useful in facilitating the diagnosis of cancer.

Correlative Light-Electron Microscopy Shows RGD-Targeted ZnO Nanoparticles Dissolve in the Intracellular Environment of Triple Negative Breast Cancer Cells and Cause Apoptosis with Intratumor Heterogeneity

ZnO nanoparticles (NPs) are reported to show a high degree of cancer cell selectivity with potential use in cancer imaging and therapy. Questions remain about the mode by which the ZnO NPs cause cell death, whether they exert an intra- or extracellular effect, and the resistance among different cancer cell types to ZnO NP exposure. The present study quantifies the variability between the cellular toxicity, dynamics of cellular uptake, and dissolution of bare and RGD (Arg-Gly-Asp)-targeted ZnO NPs by MDA-MB-231 cells. Compared to bare ZnO NPs, RGD-targeting of the ZnO NPs to integrin αvβ3 receptors expressed on MDA-MB-231 cells appears to increase the toxicity of the ZnO NPs to breast cancer cells at lower doses. Confocal microscopy of live MDA-MB-231 cells confirms uptake of both classes of ZnO NPs with a commensurate rise in intracellular Zn(2+) concentration prior to cell death. The response of the cells within the population to intracellular Zn(2+) is highly heterogeneous. In addition, the results emphasize the utility of dynamic and quantitative imaging in understanding cell uptake and processing of targeted therapeutic ZnO NPs at the cellular level by heterogeneous cancer cell populations, which can be crucial for the development of optimized treatment strategies.