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We present a phase recovery technique that utilizes a guiding method with a dynamic support to reconstruct the shape and exit wave of a single MgO nanoparticle in a coherent electron diffraction experiment. The proposed method provides an optimal solution deduced from the electron diffraction pattern alone. The recovered shape has spatial resolution 3.1 nm. The complex exit wave encodes the projected atomic structure of the nanocrystal with resolution about 0.15 nm, and agrees with a multislice simulation. The possibility of imaging nanosized objects at diffraction-limited resolution using a field emission electron microscope is thus demonstrated.

A Boersch electrostatic phase plate (BEPP) used in a transmission electron microscope (TEM) system can provide tuneable phase shifts and overcome the low contrast problem for biological imaging. Theoretically, a pure phase image with a high phase contrast can be obtained using a BEPP. However, a currently available TEM system utilizing a BEPP cannot achieve sufficiently high phase efficiency for biological imaging, owing to the practical conditions. The low phase efficiency is a result of the blocking of partial unscattered electrons by BEPP, and the contribution of absorption contrast. The fraction of blocked unscattered beam is related to BEPP dimensions and to divergence of the illumination system of the TEM. These practical issues are discussed in this paper. Phase images of biological samples (negatively stained ferritin) obtained by utilizing a BEPP are reported, and the phase contrast was found to be enhanced by a factor of approximately 1.5, based on the calculation using the Rose contrast criterion. The low gain in phase contrast is consistent with the expectation from the current TEM/BEPP system. A new generation of phase TEM utilizing BEPP and designed for biological imaging with a high phase efficiency is proposed.

Polymer‐stabilized iron oxide nanoparticles could be used as contrast agents in magnetic resonance imaging (MRI) due to their unique superparamagnetism. Here we demonstrate a quaternized chitosan, i.e. N‐[(2‐hydroxy‐3‐trimethylammonium)propyl] chitosan chloride (HTCC), encapsulating superparamagnetic iron oxide (SPIO), with very low toxicity and less effect on cell growth. HTCC has quaternary amino groups introduced into the chitosan chain, and such modification of chitosan should render it soluble in water. Most importantly, the HTCC–SPIO thus prepared has the ability to accelerate the MRI relaxation processes of surrounding water protons, resulting in enhanced MRI contrast (R2: y = 0.1076x − 0.0092; R1: y = 0.008x − 0.0005). The iron content quantified by Prussian blue staining and MRI revealed a positive correlation between Prussian blue positive cells and the change of MRI signal intensity. Also, transmission electron microscopy and element mapping confirmed intracellular metal‐like spots as internalized iron oxide. Such findings support the use of these quaternized chitosan‐stabilized iron oxide nanoparticles as a potential MRI contrast agent for cell tracking. Copyright © 2011 Society of Chemical Industry