Clinically potential proteins such as human serum albumin are utilized as single-molecule nanoreactors for fabrication of size-tunable inorganic nanoparticles or drug-loaded nanoparticles with well-defined nanostructure. The fabrication is accomplished within hollow protein nanocages through biomineralization-mediated controlled growth. These cancer-targeted protein nanoparticles are able to achieve multimodal imaging with both ultrasensitivity and spatial resolution, as well as potent cancer therapy (e.g. photothermal tumor ablation).