A new device could test blood without a needle and eliminate the long wait-time for results. The optical microscope provides high-resolution images of individual blood cells through the skin. It can reveal much of the same information as a traditional blood test by simply shining a light, without the need for harsh dyes. The microscope could help identify warning signs, such as high white blood cell counts, by scanning blood cells in motion through a probe pressed against the skin of a patient while a rainbow-like line of light is directed across a blood vessel near the surface. Researchers imaged the blood flowing through a vessel in the lower lip of a volunteer. “Since the blood cells are in constant motion, their appearance is distinctively different from the static tissue surrounding them,” Lior Golan, a biomedical engineering graduate student at the Israel Institute of Technology and one of the authors on a paper about the device, said.