Nanoparticle brain cancer therapy. Fluorescence light micrograph of nanoparticles (red) being taken up in brain tissue in the case of a glioblastoma (cancer cells in green). Treating cancer in the brain is difficult because most drug molecules are not small enough to penetrate the blood-brain barrier. Nanoparticles are one method being studied for use as a drug-delivery mechanism. This image shows nuclear DNA in blue and tumour-associated macrophages in white. The tissue is from a live rat model.