Manipulating the power of an additional phase: a flower-like Au-Fe3O4 optical nanosensor for imaging protease expressions in vivo.

We and others have recently proposed the synthesis of composite nanoparticles that offer strongly enhanced functionality. Here we have used a flower-shaped Au-Fe(3)O(4) nanoparticle as a template to construct an optical probe containing Cy5.5-GPLGVRG-TDOPA on the iron oxide surface and SH-PEG(5000) on the gold surface that can be specifically activated by matrix metalloproteinases expressed in tumors. Gold nanoparticles have excellent quenching properties, but labile surface chemistry in vivo; on the other hand, iron oxide nanoparticles afford robust surface chemistry, but are suboptimal as energy receptors. By a marriage of the two, we have produced a unified structure with performance that is unachievable with the separate components. Our results are a further demonstration that the architecture of nanoparticles can be modulated to tailor their function as molecular imaging/therapeutic agents.