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Highlights from Techniques and Biological Applications


Cryo-Scanning Electron Microscopy (SEM) and Scanning Transmission Electron Microscopy (STEM)-in-SEM for Bio- and Organo-Mineral Interface Characterization in the Environment by G Wille, J Hellal, P Ollivier, A Richard, A Burel, L Jolly, M Crampon, and C Michel, Microsc Microanl 23(6) (2017) 1159–72.


Understanding biofilm interactions with nanoparticles can benefit from the array of microscopy tools. Various approaches in biofilm preparation, labeling (cells via DAPI and extracellular polymeric substances (EPS) via lectins coupled to fluorescent dye or gold nanoparticles), and observations by fluorescent or electron microscopy were applied to study biofilm interactions with zero-valent iron nanoparticles (nZVI). Fluorescence microscopy revealed nZVI embedded in the biofilm structure as aggregates. Cryo-SEM observa- tions showed nZVI aggregates close to bacteria. STEM-in-SEM showed that nZVI aggregates could enter the biofilm to a depth of 7–11 µm. Bacteria were surrounded by a ring of EPS preventing direct nZVI/membrane interactions. EDS revealed a co-localization of nZVI with lectin-gold labeling suggesting a potential role of EPS in nZVI embedding. The combination of various microscopy approaches enabled access to the inside and outside of the biofilm at different scales of magnitude, allowing visualizations of the interactions between biofilm and nZVI. This approach allows nZVI characterization of size and aggregation inside the biofilm.


Distribution of nZVI (yellow arrow) and EPS lectin- gold labeling (red arrow) at the periphery of a biofi lm (STEM-in-SEM). Labeling was performed on the fresh biofi lm (before fi xation) using lectins coupled to gold particles. nZVI were observed as aggregates embedded in the biofi lm structure. No nZVI was observed in direct contact with bacteria, suggesting a protective role of EPS.


Techniques and Material Applications


Improved T ree-Dimensional (3D) Resolution of Electron Tomograms Using Robust Mathematical Data-Processing Techniques by T Sanders and I Arslan, Microsc Microanl 23(6) (2017) 1121–29.


Electron tomography is an essential tool for 3D characterization of nanomaterials. In recent years advances have been made in specimen preparation and mounting, acquisition geometries, and reconstruction algorithms. However, one important component of the data-processing has received less attention: the 2D tilt-series alignment. All the images need to remain coherently aligned over the full range of angles. An inaccurate alignment may be diffi cult to identify yet can signifi cantly limit the fi nal 3D resolution. T is work presents an improved center-of-mass alignment model that overcomes discrepancies from unwanted objects that enter the imaging area throughout the tilt series. In particular, an approach is developed to overcome changes in the total mass upon rotation of the imaging area. Our method is applied to accurately recover small Pt nanopar-


A comparison of one slice through a 3D reconstructed volume of Pt nanoparticles embedded in a zeolite. The same reconstruction algorithm was applied to identical input images, yet with a different interme- diate tilt series alignment step. Our alignment shows Pt particles that are distinct and clearly visible. The standard cross correlation alignment shows particles that are blurry or not present.


ticles embedded in a zeolite that might otherwise go undetected in both the 2D microscopy images and the 3D reconstruction. T is example illustrates the importance of an accurate tilt-series alignment and can increase resolution and clarity for tomograms in both physical and biological sciences.


56 doi: 10.1017/S1551929517001389 www.microscopy-today.com • 2018 March


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