Silica-coated Au@ZnO Janus particles and their stability in epithelial cells

Multicomponent particles have emerged in recent years as new compartmentalized colloids with two sides of different chemistry or polarity that have opened up a wide field of unique applications in medicine, biochemistry, optics, physics and chemistry. A drawback of particles containing a ZnO hemisphere is their low stability in biological environment due to the amphoteric properties of Zn²⁺. Therefore we have synthesized monodisperse Au@ZnO Janus particles by seed-mediated nucleation and growth whose ZnO domain was coated selectively with a thin SiO₂ layer as a protection from the surrounding environment that imparts stability in aqueous media while the Au domain remained untouched. The thickness of the SiO₂ layer could be precisely controlled. The SiO₂ coating of the oxide domain allows biomolecule conjugation (e.g. antibodies, proteins) in a single step for converting the photoluminescent and photocatalytic active Janus nanoparticles into multifunctional efficient vehicles for cell targeting. The SiO₂-coated functionalized nanoparticles were stable in buffer solutions and other aqueous systems. Biocompatibility and potential biomedical applications of the Au@ZnO@SiO₂ Janus particles were assayed by a cell viability analysis by co-incubating the Au@ZnO@SiO₂ Janus particles with epithelia cells and compared to those of uncoated ZnO.