AFM characterization of spin-coated multilayered dry lipid films prepared from aqueous vesicle suspensions

We present a detailed AFM study on multilayered dry lipid films prepared from aqueous vesicle suspensions. Different preparation techniques were applied in order to optimize the preparation of homogeneous lipid films of various film thicknesses. Suspensions of preformed DOPC/DPPC vesicles were adsorbed onto indium tin oxide-coated glass coverslips, a substrate also commonly employed for the formation of giant liposomes. We found that the homogeneity of the lipid films could substantially be improved when applying a spin-coating step during the film preparation. These films were much more homogeneous than those prepared by conventional drop-casting and in addition the film thickness could be controlled. When using a combination of vesicle adsorption and spin-coating the quality and thickness of the films depended crucially on the lipid concentration of the vesicle suspension, the adsorption temperature and the adsorption time. For lipid films prepared by direct spin-coating the lipid concentration and the applied spin-coating sequence were critical parameters for the quality and thickness of the deposited lipid films.     

Liposome delivered and polymeric metal complexes as potential sensitizers for the photodynamic therapy of cancer

Different possibilities of macromolecular metal complexes as photosensitizers (PS) for their potential use in the photodynamic therapy of cancer are described. The prepared metal porphyrazin derivatives (metals: Zn(II), Si(IV)(X)₂) exhibit long wavelength absorption and high singlet oxygen quantum yields under irradiation. One possibility is the incorporation of the PSs in liposomal vesicles giving hydrophobic conjugates with low densitiy proteins in the serum after injection. Good tumor accumulation and photodynamic activities are observed. Increased tumor uptake is also known for Pcs covalently connected via the ligand to poly(ethylene glycol monomethyl ether). New compounds contain the hydrophilic polymer at axial substituents of Si(X)₂Pc and Si(X)₂Nc. Some newly synthesized compounds with only one functional group exhibit the possibility of coupling to macromolecules like e.g. monoclonal antibodies.