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The genomes of most protozoa encode families of variant surface antigens, whose mutually exclusive changes in expression allow parasitic microorganisms to evade the host immune response1,2. It is widely assumed that antigenic variation in protozoan parasites is accomplished by the spontaneous appearance within the population of cells expressing antigenic variants that escape antibody-mediated cytotoxicity1,2. Here we show, bothin vitroand in animal infections, that antibodies to Variant-specific Surface Proteins (VSPs) of the intestinal parasiteGiardia lambliaare not cytotoxic, inducing instead VSP clustering into liquid-ordered phase membrane microdomains that trigger a massive release of microvesicles carrying the original VSP and switch in expression to different VSPs by a calcium-dependent mechanism. Surface microvesiculization and antigenic switching are also stimulated whenTrypanosoma bruceiandTetrahymena thermophilaare confronted to antibodies directed to their GPI-anchored variable surface glycoproteins. This novel mechanism of surface antigen clearance throughout its release into microvesicles coupled to the stochastic induction of new phenotypic variants not only changes the current paradigm of spontaneous antigenic switching but also provides a new framework for understanding the course of protozoan infections as a host/parasite adaptive process.

The fate and effect of nanomaterials in the environment is of paramount importance towards the technological application of the materials. This work shows the ecotoxicological potential of polyaniline (PANI) nanofibers in the larvae Rhinella arenarum by means of AMPHITOX test. Acute toxicity of PANI nanofibers towards embryos of the common South American toad R. arenarum (Anura: bufonidae) was evaluated in the premetamorphosis (stage 25) larvae. The exposure of R. arenarum larvae to at dose of 150, 250 and 400 mg L−1 resulted in 100% viability within 96 h exposure. The embryos at 2–4 blastomers stage (early life stage teratogenic test) revealed that embryos were not killed and no teratogenic effects were observed when embryos were incubated with PANI nanofibers (150 and 250 mg L−1), while only a growth retardation of embryos was induced at levels of 250 mg PANI nanofibers L−1. On the other hand, at 400 mg L−1 concentration, a reduction in the body length of larvae and tail malformation was observed. This results suggest that a concentration-dependent toxicity is operative, typified by phenotypes that had abnormal body axes. The presence of PANI nanofibers in gut contents and its excretion by larval stages of R. arenarum was confirmed by UV–visible spectroscopy.

Two different approaches are used to produce conducting polymer nano-objects. One is a “top-down” approach which involves laser ablation of conducting polymer films using laser light interference patterns (direct laser interference patterning, DLIP) to produce various surface shapes, including nanowires and nanodots. Polyaniline(PANI) and polypyrrole (PPy) nanostructures could be easily produced by ablation of films, previously formed by in-situ polymerization of the aromatic monomers. The other is a “bottom-up” approach involving the controlled nucleation and growth during monomer polymerization. This is achieved by performing the polymerization at the interface of two immiscible solvents. Both kinds of nanomaterials are characterized using dynamic light scattering, TEM, EDAX, FTIR, UV-vis and fluorescence spectroscopy. The structures are studied by SEM-FIB, optical and fluorescence microscopy along with water contact angle. It is shown that nanometric sized structures can be made by both methods. The ch...

Layers of multiwall carbon nanotubes (MWNT), with different thickness, are built by sequential drop coating of a MWNT-Nafion ® dispersion in ethanol onto glassy carbon substrates. The layers form a 3D conductive network towards the electrochemical reactions of soluble redox couples (Fe 3+/2+ ) in aqueous solutions. Digital simulation of the electrochemical response suggests that the electron transfer is controlled by finite diffusion of the redox species inside the network. It is possible to create an interpenetrated network of carbon nanotubes and electroactive polymers (poly(hydroxynaphtoquinones)) by electropolymerization in nonaqueous media, which are electroactive in aqueous and nonaqueous media. The electrochemical response, both in cyclic voltammetry (CV) and square wave voltammetry (SWV), is significantly increased. In that way, the sensitivity of sensors (e.g. DNA biosensors based on the change of electroactive polymer response upon hybridization) could be improved.