This fluorescence microscopy image shows the distribution of two nanoparticles pumped gently into the brain. One particle (red) bound to brain tissue near the site of infusion while the other particle penetrated outwards several millimeters (green). Nanoparticles can be filled with either drugs or DNA for treatment of diseases including brain tumors, Alzheimer's, and Parkinson's. Visual studies like this help determine what properties are best suited to deliver therapy to these diseases. Source: Frank Szoka, Jr. and J. A. MacKay, University of California at San Francisco