Polyelectrolyte multilayer capsule formation

Enzyme based micron sized sensing system with optical readout was fabricated by co-encapsulation of urease and dextran couple with pH sensitive dye SNARE-1 into polyelectrolyte multilayer capsules. The co-precipitation of calcium caibonate, urease, and dextran followed up by multilayer film coating and Ca- extracting by EDTA resulted in formation of 3.5-4 micron capsules, what enable the calibrated fluorescence response to urea in concentration range from 10 to 10 M. Sensitivity to urea in concentration range of 10 to 10 M was monitored on capsule assemblies (suspension) and on single capsule measurements. Urea presence can be monitored on single capsule level as illustrated by confocal fluorescent microscopy. 

Different colloidal cores can be decomposed after multilayers are assembled on their surface. If the products of core decomposition are small enough to expel out of polyelectrolyte multilayer the process of core dissolution leads to formation of hollow polyelectrolytes shells (Fig. 2.1, d-f). Up to now, various colloidal templates such as organic and inorganic cores, like MF-particles, organic crystals, carbonate particles and biological cells were used as templates for hollow capsule fabrication. Decomposition can be done by different means, such as low pH for MF- and carbonate particles [43], organic water miscible solvents for organic crystals [44] and... 

Studies on PEM are of interest because of the versatility of multilayer formation process with respect to variety of support materials, combination with other assembly techniques and possibility of incorporation of different functional species [1-4]. PEM are applied in chemical and biochemical sensing or preparation of new biomaterials. When colloidal particles or emulsion droplets are used as cores for polyelectrolyte deposition one can obtain hollow micro- and nanocapsules. Such capsules have potential as drug delivery systems [5] capable of sustained release [6,7], microreactors [8,9] or catalytic systems [8-10]. Detailed summaries on the properties and application of PEM prepared by LbL technique can be found in [1,11]. 

Fig. 21 (a) Photoreduction of Ag on the surface of the (polyaniline-PSS/PAH)4 shells. Inset (polyaniline-PSS/PAH)4 capsules after the addition of AgN03 and photo-irradiation of the lower capsule (arrow). Scale bar 10 nun. Reprinted with permission from [137] Copyright 2002 American Chemical Society (b) Formation of palladium NPs in a multilayered polyelectrolyte film on colloids. Reprinted with permission from [138] Copyright 2004 American Chemical Society... 

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