Flower-like Au-Fe3O4 optical nanosensor for imaging protease expressions in vivo

History has witnessed an enormous progress of developing nanocrystals into “smart” probes for either imaging or therapeutic applications. Such progress is in large part powered by our ability to manipulate the surface of nanoparticles, marked by the establishment of surface engineering techniques that permit facile docking of functional motifs onto particles. However, these techniques have been increasingly challenged by the growing needs of imparting multiple motifs onto a single nanoplatform without disturbing the balance among the particles´ physiological stability, target specificity and biological activity. Biphasic composite nanoparticles yield a multiplied combination of structural and functional parameters thereby providing greater flexibility in the design of nanogadgets. Here we have used a flower-shaped Au-Fe₃O₄ nanoparticle as a template to construct an optical probe that can be specifically activated by matrix metalloproteinases (MMPs) expressed in tumors. Gold nanoparticles have excellent quenching properties but labile surface chemistry in an in vivo environment; on the other hand, iron oxide nanoparticles afford robust surface chemistry but are suboptimal as energy receptors. By the marriage of the two, we have been able to combine the strengths of each component to yield a unified structure with a desired performance that would not be achievable with the separate components. Our results demonstrate that the architecture of nanoparticles can be modulated to tailor their function as molecular imaging/therapeutic agents.