Elemental mapping by electron energy loss spectroscopy in biology.

Over the past decades there have been significant advances in transmission electron microscopy for biological applications, including in energy filtering and spectrum imaging, which are techniques based on the principles of electron energy loss spectroscopy. These imaging modalities allow quantitative mapping of specific chemical elements with high sensitivity and spatial resolution. This chapter describes the experimental and computational procedures for elemental mapping in two dimensions as well as a more recent extension to three dimensions, which can reveal quantitative distributions of elements in cells on a macromolecular scale.

Self-aligned wet-cell for hydrated microbiology observation in TEM.

This paper describes a Self-Aligned Wet (SAW) cell suitable for direct-cell or bacteria incubation and observation in a wet environment inside a transmission electron microscope. This SAW cell is fabricated by a bulk-micromachining process and composed of two structurally complementary counterparts (an out-frame and an in-frame), where each contain a silicon nitride film based observation window. The in- and out-frames can be self-aligned via a mechanism of surface tension from a bio-sample droplet without the aid of positioning stages. The liquid chamber is enclosed between two silicon nitride membranes that are thin enough to allow high energy electrons to penetrate while also sustaining the pressure difference between the TEM vacuum and the vapor pressure within the liquid chamber. A large field of view (150 µm × 150 µm) in a SAW cell is favored and formed from a larger sized observation window in the out-frame, which is fabricated using a unique circular membrane formation process. In this paper, we introduce a novel design to circumvent the challenges of charging/heating problems in silicon nitride that arise from interactions with an electron beam. This paper also demonstrates TEM observations of D. Radiodurans growth in a liquid environment within a thicker chamber (20 µm) within a SAW cell.

Size characterization of drug-loaded polymeric core/shell nanoparticles using asymmetrical flow field-flow fractionation.

Asymmetrical flow field-flow fractionation (AsFlFFF) was used to determine the size distribution of drug-loaded core/shell nanoparticles which have a lipid core of lecithin and a polymeric shell of a Pluronic. AsFlFFF provided separation of the drug-loaded core/shell nanoparticles from smaller coreless polymeric micelles, thus allowing accurate size analysis of the drug-loaded nanoparticles without interference by the coreless micelles. It was found from AsFlFFF that the drug-loaded nanoparticles have broad size distributions ranging from 100 to 600 nm in diameter. It was also found that, after the nanoparticles had been stored for 70 days, they disappeared as a result of self-degradation. Being a separation technique, AsFlFFF seems to be more useful than transmission electron microscopy or dynamic light scattering for size analysis of core/shell nanoparticles, which have broad and bimodal size distributions. [figure: see text]