The Size and Morphological Study of Spherical Polyelectrolyte Complex Beads Using Environmental Scanning Electron Microscopy

Abstract

Development of new polyelectrolyte complex (PEC) capsules/beads for biotechnological applications such as the immunoisolation of Langerhans islets for the treatment of diabetes and the stabilization and reuse of enzymes and bacterial cells as biocatalysts is very important [1]. Morphological characterization and study of PEC beads properties represents important challenge for electron microscopy. These very beam-sensitive bio-polymer capsules used for immobilization of cells are laboratory produced as a uniform with a controlled shape, size, membrane thickness, permeability and mechanical resistance [1]. Owing to importance to study above mentioned parameters, samples must be inspected in their fully native and functional state. It means free of freezing, chemical contamination or preparation, shape distortion and in thermodynamically stabile and fully wet state, precisely reached after very slow changing of conditions in the specimen chamber of ESEM. Violation of these conditions leads to deformation and burst of thin semipermeable membrane surrounding liquid core, containing live bacterial cells, for example E. coli. The aim of this work is to prove ability to use our non-commercial ESEM AQUASEM II for inspection and developmental support of this type of samples and demonstrate their sensitivity on two types of PEC beads prepared from alternative materials.PEC beads has been produced by air-stripping nozzle via polyelectrolyte complexation (20 min) of sodium alginate and cellulose sulphate (CS) as polyanions, poly(methylene-co-guanidine) as a polycation, CaCl 2 as a gelling agent and NaCl as an antigelling agent [1] without the use of a multiloop reactor. Two different sources of CS have been tested for preparation of PEC beads (CS from Across Organics, N.J., USA; Fig. 1) and alternative PEC beads (tailor-made CS from Senova, Weimar, Germany; Fig 2). Due to the relatively big size of samples (800m in diameter) and their beam sensitivity, a combination of our newly published method [2] and special improvement of our ionization detector of SE were used. The gentle and slow sample chamber pumping procedure [2] and our ionization detector of SEs [3] (beam current up to 40 pA) enhanced for larger field of view (850 μm) were combined. Samples were observed in small droplet (approximately 10 l) of distilled water. Both types of matrices were observed at sample to second pressure limiting aperture distance 4 mm. For thermodynamic equilibrium adjustment control, Pfeiffer pressure gauges CMR 261 and CMR 263, a custom build Peltier stage and a hydration system were used.

Non-invasive Morphological and Elemental Analysis of Ivory Plate for Artworks Authentication Using ESEM and EDS

“…In the case of miniature painting only non-invasive approaches of the analysis should be carried out. These nonconductive samples could be very susceptible to environmental and electron beam conditions [3]. ESEM is suitable method allowing using optimal environmental humidity to protect sample drying, cracking or potential chemical modification.…”