Chemosensors and biosensors based on polyelectrolyte microcapsules containing fluorescent dyes and enzymes

The concept of enzyme-assisted substrate sensing based on use of fluorescent markers to detect the products of enzymatic reaction has been investigated by fabrication of micron-scale polyelectrolyte capsules containing enzymes and dyes in one entity. Microcapsules approximately 5 μm in size entrap glucose oxidase or lactate oxidase, with peroxidase, together with the corresponding markers Tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) dichloride (Ru(dpp)) complex and dihydrorhodamine 123 (DHR123), which are sensitive to oxygen and hydrogen peroxide, respectively. These capsules are produced by co-precipitation of calcium carbonate particles with the enzyme followed by layer-by-layer assembly of polyelectrolytes over the surface of the particles and incorporation of the dye in the capsule interior or in the multilayer shell. After dissolution of the calcium carbonate the enzymes and dyes remain in the multilayer capsules. In this study we produced enzyme-containing microcapsules sensitive to glucose and lactate. Calibration curves based on fluorescence intensity of Ru(dpp) and DHR123 were linearly dependent on substrate concentration, enabling reliable sensing in the millimolar range. The main advantages of using these capsules with optical recording is the possibility of building single capsule-based sensors. The response from individual capsules was observed by confocal microscopy as increasing fluorescence intensity of the capsule on addition of lactate at millimolar concentrations. Because internalization of the micron-sized multi-component capsules was feasible, they could be further optimized for in-situ intracellular sensing and metabolite monitoring on the basis of fluorescence reporting.     

Macromolecule Loading into Spherical,Elliptical, Star‐Like and Cubic Calcium Carbonate Carriers

We fabricated calcium carbonate particles with spherical, elliptical, star‐like and cubical morphologies by varying relative salt concentrations and adding ethylene glycol as a solvent to slow down the rate of particle formation. The loading capacity of particles of different isotropic (spherical and cubical) and anisotropic (elliptical and star‐like) geometries is investigated, and the surface area of such carriers is analysed. Potential applications of such drug delivery carriers are highlighted.     

Preparation of polyelectrolyte microcapsules with silver and gold nanoparticles in a shell and the remote destruction of microcapsules under laser irradiation

A number of methods are proposed for encapsulating silver and gold nanoparticles into shells of polyelectrolyte microcapsules for the purpose of increasing the sensitivity of microcapsules to laser radiation. It is shown that capsules with nanocomposite shells can be remotely damaged under laser radiation with different powers and wavelengths. The sensitivity of capsules with silver and gold nanoparticles in shells to this radiation can be controlled by varying the conditions used for the preparation of the capsules. The release of the encapsulated material under laser radiation makes these systems promising for use as microcontainers intended for the target delivery of drugs in an organism.     

A kinematical study of Kirchhoff-Rayleigh flow

Summary A method of calculating the separated flow of a viscous fluid is proposed, which allows to split up properly the boundary condition problem from the viscous phenomena. The theory is developed for the flow past a plate and yields wakes of finite extension having an underpressure which depends directly on the amount of vorticity diffusion and dissipation occurring in the fluid. Application of the method to real flows shows good agreement between the calculated and the measured velocity distributions in front of the plate and in the wake.

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Résumé Une méthode de calcul de l'écoulement décollé d'un fluide visqueux est proposée qui permet de séparer clairement le problème aux limites des phénomènes visqueux. La théorie est développée pour l'écoulement autour d'une plaque et donne des sillages de longueur finie ayant une dépression de culot directement dépendante de l'intensité de la diffusion et dissipation de la vorticité se produisant dans le fluide. L'application de la méthode à des écoulements réels montre une bonne concordance entre les répartitions de vitesse calculées et mesurées sur le devant de la plaque et dans le sillage.

     

Reversibly permeable nanomembranes of polymeric microcapsules

Polymeric nanometer-thick membranes or nanomembranes possessing photocontrollable permeability are presented. Microcapsules are used as membrane model systems, while gold nanoparticle aggregates are used as active absorption centers. Upon laser light illumination the membranes change permeability reversibly because nanoparticles transiently affect the nearby polymeric network. Nanomembranes reseal to their impermeable state when the laser is switched off. This presents a novel and simple way of reversible permeability control of interest to intracellular signaling and membranes.