Researchers from Massachusetts General Hospital and Harvard Medical School have developed a microfluidic device that can be used as an alternative to flow cytometry for measuring T cell counts in people infected with HIV. They hope that the small handheld device will help Africans — it will first be tested in Rwanda — in poor regions to better manage their disease. The device consists of a chip lined with a channel, on which are spotted molecules that bind to CD4, a protein found on T cells; a simple light microscope then counts the cells.