An inexpensive ultrasonic generator (household humidifier; ultrasonic spray pyrolysis) is used to synthesize porous, hollow, and ball-in-ball metal oxide microspheres (see figure). The morphology and pore size were controlled by the silica to Ti-IV ratio and silica particle size. With the introduction of transition-metal ions, core/shell-type microspheres can be synthesized in a single-pot synthesis. These nanomaterials are rapidly taken up into the cytoplasm (but not into the nucleus) of macrophages and show very little cell toxicity.