LAYER-BY-LAYER CONSTRUCTED POROUS ARCHITECTURES
High molar mass double-stranded DNA, a negatively charged polyelectrolyte, and cationic poly(ferrocenylsilane) were employed in a layer-by-layer deposition process to form porous structures on flat and on curved substrates. On planar substrates, initial DNA/PFS bilayers exhibited an irregular, web-like morphology. This 2-dimensional DNA network spontaneously evolved with increasing the number of deposited polyelectrolyte layers into a 3-dimensional hierarchical structure (Figure 1).
Figure 1. Tapping mode Atomic Force Microscopy (AFM) height images of silicon wafers with a) polyethyleneimine (PEI) layer; b) PEI + one DNA/PFS bilayer (DNA/PFS)1; c) PEI + five DNA/PFS bilayers (DNA/PFS)5; d) PEI + (DNA/PFS)10, showing the development of a 3-dimensional porous structure with an increasing number of polyelectrolyte bilayers. e) Top-view SEM image of a PEI + (DNA/PFS)10 film on silicon. The scale bar represents 1 ym.
Colloidal particles of manganese carbonate were covered with DNA/PFS multilayers (SEM image, Figure 2) as reported in Angew. Chem. Int. Ed. 2007, 46, 1702-1705, and on the inside cover of this journal (p. 1546). Removal of the templating core produced microcapsules with a porous wall. Confocal laser scanning microscopy showed that unlike conventional capsules, these DNA/PFS microcapsules display complete permeability to large molecules (66000 g mol-1 dextran, hydrodynamic radius 9 nm) and macromolecules (MRho-PSS, 120000 g mol-1).
Figure 2. Colloidal particles of manganese carbonate covered with multilayers of high-molar-mass double-stranded DNA and cationic poly(ferrocenylsilane) (PFS) polyelectrolytes (SEM image). The macroporous structures, confirmed also by AFM (inset image) were constructed by simple sequential supramolecular assembly controlled by the persistence length mismatch of the constituents. Upon MnCO3 core removal porous capsules were obtained.
The electrostatic self-assembly of polyelectrolytes with a high persistence length and chain length mismatch demonstrated here constitutes a new method for the fabrication of bio-compatible porous structures, which may have potential applications in new cell scaffold materials, gene therapy, biocompatible surfaces, and controlled, active, molecular release systems.
Publication Y. Ma, W.-F. Dong, M.A. Hempenius, H. Möhwald, G.J. Vancso, Layer-by-Layer Constructed Macroporous Architectures, Angewandte Chemie International Edition 2007, 46, 1702-1705.