Laser mediated remote release of encapsulated fluorescently labeled polymers from nanoengineered polyelectrolyte multilayer capsules containing gold sulfide core/gold shell nanoparticles in their walls is observed in real time on a single capsule level. We have developed a method for measuring the temperature increase and have quantitatively investigated the influence of absorption, size, and surface density of metal nanoparticles using an analytical model. Experimental measurements and numerical simulations agree with the model. The treatment presented in this work is of general nature, and it is applicable to any system where nanoparticles are used as absorbing centers. Potential biomedical applications are highlighted.

Hollow polyelectrolyte microcapsules made of poly(allylamine hydrochloride) and sodium poly(styrene sulfonate), templated on various cores, manganese and calcium carbonate particles or polystyrene latexes, were investigated. The polyelectrolyte multilayers respond to a change of pH, leading to a swelling of the capsules in basic conditions and a further shrinking when the pH is reduced to acidic. The nature of the core and the subsequent dissolution process have an influence on this pH responsiveness, and the structuring effect of tetrahydrofuran on the multilayers has been demonstrated. Increasing the molecular weight of the polymers or the number of layers causes also a rigidification of the structure and modifies the pH response.

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Summary: We investigated microcapsules composed of the weak polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) (PMA) assembled on calcium carbonate cores. These capsules are stable in the pH range from 2.5 to 11.5, undergoing reversible swelling in the pH interval from 2.7 to 2.6. Capsule swelling occurs at a protonation degree above 90%. The pH‐dependent size variation of PAH/PMA capsules is blocked after crosslinking of the polyelectrolyte layers.Schematic of the swelling and de‐swelling of the capsules with changing pH.imageSchematic of the swelling and de‐swelling of the capsules with changing pH.

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Hollow microcapsules composed of the weak polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) (PMA) are templated on silicon oxide particles using the layer-by-layer adsorption. The colloidal template is removed with a buffer system of hydrofluoric acid and ammonium fluoride. With this buffer system, the template can be dissolved in mild pH conditions, where the polymeric layers are still stable. The morphology and the thickness of the resulting capsules are investigated with atomic force microscopy. The resulting hollow capsules show pH-dependent properties. The shells are stable over a broad pH range and swell and immediately dissolve for pH values below 2.3 and above 11. If the molecular weight of the poly(methacrylic acid) is increased, the enhanced entanglement of the polymers results in a reversible swelling of the capsules at low and at high pH. The swelling degree is probed with confocal laser scanning microscopy. In addition to the pH-dependent size variations, the different ionization degree of poly(methacrylic acid) as a function of pH is used for the selective binding of calcium ions.

Carbohydrate‐sensitive polymer multilayers are assembled onto flat substrates and colloidal CaCO3 particles via reversible covalent ester formation between the polysaccharide mannan and phenylboronic acid moieties grafted onto poly(acrylic acid) (PAA). The resulting multilayer films are sensitive to several carbohydrates, and show the highest sensitivity to fructose. The response to carbohydrates arises from the competitive binding of small molecular weight sugars and mannan to boronic acid groups within the films, and is observed as a rapid dissolution of the multilayers upon contact with a sugar‐containing solution above a critical concentration. In addition, carbohydrate‐sensitive multilayer capsules are prepared, and their sugar‐dependent stability is investigated by following the release of encapsulated tetramethylrhodamine isothiocyanate‐bovine serum albumin (TRITC‐BSA).

Aggregation states of both stabilized (by organic ligands) and nonstabilized nanoparticles have been studied in solutions, on plain surfaces, and within the polyelectrolyte multilayer capsules to provide control over formation of aggregates and their uniformity. Adsorption of nanoparticles could be performed either simultaneously with polymers to achieve their uniform (nonclustered or nonaggregated) distribution or without polymers for obtaining nonuniform (clustered or aggregated) distribution. Nanoparticles were characterized; in synthesis of nanoparticles involving gold sulfide the reaction can be stopped at a desired time to control the location of the near-infrared absorption peak. The influence of the uniformity of the nanoparticles distribution on the temperature rise during laser light illumination is numerically calculated; it is shown that the temperature rise on the closely located nanoparticles is higher than on the stand-alone nanoparticles. Further applications of polymer controlled distribution of nanoparticles are anticipated in their self-assembly.