Reduction of Self-Quenching in Fluorescent Silica-Coated Silver Nanoparticles

This paper reports the development of spherical Ag@SiO₂ nanocomposites in which fluorescein isothiocyanate molecules have been incorporated using a silane coupling agent and a straightforward microemulsion-based synthesis procedure. The photophysical characteristics of core-shell and coreless nanostructures with similar silica shell thickness and fluorophore densities are measured and compared, and show unequivocally that the presence of the silver core decreases the fluorophore lifetime by a factor as high as 4 and that the steady-state fluorescence intensity is increased by a factor as high as 3. The relationship between the enhancement in fluorescence yield and the influence of the silver core on resonance energy transfer processes was examined by fluorescence lifetime and anisotropy measurements. These Ag@SiO₂ core-shell nanoparticles provide higher detectability and lower self-quenching, whereas the faster recycling time offers more robustness toward photobleaching.     

Global stability and optimisation of a general impulsive biological control model

An impulsive model of augmentative biological control consisting of a general continuous predator-prey model in ordinary differential equations, i.e. a meta-model, augmented by a discrete part describing periodic introductions of predators is considered. The existence of an invariant periodic solution that corresponds to prey eradication is shown and a condition ensuring its global asymptotic stability is given. An optimisation problem related to the preemptive use of augmentative biological control is then considered. It is assumed that the per time unit budget of biological control (i.e. the number of predators to be released) is fixed and the best deployment of this budget is sought in terms of release frequency. The cost function to be minimised is the time needed to reduce an unforeseen prey (pest) invasion occurring at a worst time instant under some harmless level. The analysis shows that the optimisation problem admits a countable infinite number of solutions. An argumentation considering the required robustness of the optimisation result with respect to the invasive prey population level and to the model parameters is then conducted. It is shown that the cost function is decreasing in the predator release frequency so that the best deployment of the biocontrol agents is to carry out as frequent introductions as possible.     

Surveillance des patients sous AVK : les laboratoires s’impliquent

Un accord a été signé pour un meilleur suivi des patients sous antivitamine K (AVK) entre les syndicats de biologie libérale et la CNAM dans l’avenant à la convention nationale paru au Journal Officiel du 27 février 2003⋆. Le Pr Ludovic Drouet⋆⋆ nous fait part de sa réaction et de ses attentes suite à cet engagement de la profession.     

Alterations in Peripheral Blood B Cell Subsets and Dynamics of B Cell Responses during Human Schistosomiasis

Antibody responses are thought to play an important role in control of Schistosoma infections, yet little is known about the phenotype and function of B cells in human schistosomiasis. We set out to characterize B cell subsets and B cell responses to B cell receptor and Toll-like receptor 9 stimulation in Gabonese schoolchildren with Schistosoma haematobium infection. Frequencies of memory B cell (MBC) subsets were increased, whereas naive B cell frequencies were reduced in the schistosome-infected group. At the functional level, isolated B cells from schistosome-infected children showed higher expression of the activation marker CD23 upon stimulation, but lower proliferation and TNF-α production. Importantly, 6-months after 3 rounds of praziquantel treatment, frequencies of naive B cells were increased, MBC frequencies were decreased and with the exception of TNF-α production, B cell responsiveness was restored to what was seen in uninfected children. These data show that S. haematobium infection leads to significant changes in the B cell compartment, both at the phenotypic and functional level.     

Rhodamine B as a collective marker for studying movements of small mammals

We present a new method of collective marking (rhodamine B) of small mammals that can be used under natural conditions. We examine the acceptance of marked baits, detection and persistence of the signal on the different kinds of hairs of two small species of rodents. Rhodamine B was ingested by captive animals and their hairs were dyed a fluorescent red coloration and observed over more than 150 days. Preliminary results obtained under field conditions tend to demonstrate that winter and summer movements could be detected by this technique. This new collective marking technique may be of great interest to study population turnover and movements of small mammals between habitat patches; it may represent an important method of assessing connectivity and permeability of landscapes by small mammals.     

Real-life Lernaean Hydras: a practical activity about the effects of oxygen concentration on regenerative capabilities of planarians

ABSTRACT

Changes in environmental conditions can have a profound impact on organismal processes. For aquatic organisms, changes in dissolved oxygen concentration can have major repercussions, notably for physiological processes that have high long-term energetic costs and are more likely to rely on aerobic metabolic pathways. Here we propose a simple college or university-level low-cost laboratory activity that addresses the effect of differences in oxygen concentration on an important physiological property of planarian flatworms: their regeneration capacity. Students were asked to perform measurements and statistically compare the efficacy of the regeneration process between planarians kept in normoxic conditions and others kept in hypoxic conditions. The activity was evaluated by asking students to produce a short laboratory report with all of the sections that a scientific article generally comprises. This hands-on experiment has the benefit of going beyond how planarians are traditionally used in biodiversity classes (i.e. basic anatomy of flatworms) by combining behavioural, physiological and environmental observations while investigating the effects of an environmental variable on the regeneration response. We would further encourage professors to expand even more upon this framework by providing the students with an opportunity to actively engage in all steps inherent to the scientific process.