Metallosomes: artificial cell membranes with ultrathin metallic surfaces derived from cationic cerasomes through electroless plating

Novel liposomal membranes having a metallic surface, so-called metallosomes, were prepared by electroless plating of cationic cerasomes, recently developed as organic-inorganic vesicular nanohybrids. The electroless plating of cerasomes was performed by firstly binding PdCl4 2- ions onto the cationic membrane surface through electrostatic interactions, then subsequently reducing this precursor catalyst to Pd(0), and finally, depositing a layer of metal onto the cerasome surface using an appropriate plating bath. While metallosomes coated with an ultrathin Ni layer could be prepared by electroless Ni plating of cationic cerasomes, it was not possible to derive the corresponding Ni-coated vesicles from the liposomal membranes formed with cationic peptide lipids under similar plating conditions, thus reflecting the difference in the morphological stability of these vesicles. The characterization of the Ni-metallosomes was performed using various physical measurements such as scanning and transmission electron microscopies, energy-dispersive X-ray spectroscopy, electron energy-loss spectroscopy, and electron tomography. The Ni layer thickness was controllable on the nanometer scale by changing the plating time. The gel to liquid-crystalline phase transition behavior of the Ni-metallosomes was observed by differential scanning calorimetry, indicating that the metallosomes maintain their lipid bilayer membranes. Ni-metallosomes with various sizes were prepared from the corresponding cerasomes in a diameter range of 50-5000 nm. Metallosomes with an Au layer were also successfully obtained by electroless Ni/Au substitution plating of Ni-metallosomes.