Being able to safely destroy or reprogram very specific cell populations will enable a wide range of very useful therapies. Here's an example of what's going on in the labs these days: researchers "have developed the basis for a four-in-one agent that can detect, target, and disable tumor cells while also making them [visible]. ... their work involves magnetic iron oxide particles with a fluorescence dye, RNA fragments, and a special peptide attached. The peptide is present to specifically identify the cancer cells; the RNA fragments suppress the special cancer-cell genes, killing the cells. The magnetic particles act as a contrast agent for magnetic resonance imaging, and the fluorescence dye allows for microscopic imaging of the target cells. ... mRNA is a good point of attack to stop the synthesis of proteins required for tumor growth. To achieve this, siRNAs (small interfering RNAs) are introduced into the cell. ... When bound to nanoparticles, the siRNAs are easier to slip into cells. In order to specifically target cancer cells, the particles carry a short peptide, called RGD, which points the way: RGD strongly binds to an integrin, a membrane protein that is anchored to metastasizing tumor cells in much higher amounts than in healthy tissue. The integrins with RGD-equipped nanoparticles are actively brought into the cell interior with their cargo intact."