MACROMOLECULAR ENGINEERING AND NANOFABRICATION OF REDOX STIMULUS RESPONSIVE CAPSULES FOR PERMEABILITY CONTROL
Organometallic, iron containing, stimulus responsive “smart” polymers were used to fabricate responsive micro- and nanocapsules. The hollow containers were made in water by electrostatic layer-by-layer self-assembly. In this process positively and negatively charged polyions are sequentially assembled on top of each other using a microsphere template, which is chemically removed upon completion of the assembly process. The thin walls of the capsules obtained are held together by electrostatic interactions, and have a molecular permeability, which can be controlled by changing the oxidation state of iron in the polymer chains. Thus the capsules allow one to capture, retain and release molecules of predetermined sizes. Permeability of the capsule walls, thus the size of the molecules that can enter or leave the capsules, is determined by the number of polyionic layers and by the oxidation state of iron. Potential applications include biomedical and biological use, and in other „green” areas such as encapsulation and release of food additives, drugs, cosmetic agents, and in fundamental science such as in bionanochemistry, e.g. to encapsulate (and protect) single enzyme catalyst molecules and monitor their reaction in confinement with other molecules within the nanocontainers. If large numbers of containers are used simultaneously, and addressed individually, synthetic or natural catalysts may be compared and selected for optimum efficiency using the cages as nanoreactor vessels in fast, parallel, so-called high throughput combinatorial chemistry experiments.
Confocal fluorescence microscopy images of empty (left) and loaded (right) PFS capsules (Copyright by Y. Ma, W.-F. Dong, M.A. Hempenius, H. Möhwald, G.J. Vancso; published with permission)
Publication Y. Ma, W.-F. Dong, M.A. Hempenius, H. Möhwald, G.J. Vancso, Redox-Controlled Molecular Permeability of Composite-Wall Microcapsules, Nature Materials, 5, 724-729 (2006) See also www.nanowerk.com