A new method for the synthesis of magnetoliposomes

A new method for the synthesis of magnetoliposomes, i.e., nanosized magneti c particles coated by a phospholipid membrane, is presented. Magnetoliposom es are prepared by directly using the phospholipid vesicles as nanoreactors for the precipitation of the magnetic particles. The magnetoliposomes have been characterized using transmission electron microscopy imaging and x-ra y powder diffraction. The magnetic properties of the magnetoliposomes have been investigated with a superconducting quantum interference device magnet ometer. Our results indicate that the magnetoliposomes contain approximatel y spherical maghemite nanoparticles averaging 25 nm in diameter. The occurr ence of a phospholipid bilayer surrounding the magnetic particles is confir med both by transmission electron micrographs of samples negatively stained with uranyl acetate and by digital fluorescence imaging microscopy measure ments of magnetoliposomes labeled with fluorescein. The temperature depende nce of the zero field cooled and field cooled susceptibilities of the magne toliposomes is consistent with their expected superparamagnetic nature. (C) 1999 American Institute of Physics. [S0021-8979(99)42808-7].