Using inexpensive glass beads traditionally used for reflective pavement markings at airports, the PNNL team has demonstrated 1000x magnification, which is necessary to see tiny anthrax spores and plague cells. They have also made a 350x version, which is adequate to identify parasites in blood samples or protozoa in drinking water. A 100x version enables children to investigate common items like salt grains and flower petals in much greater detail.

via PNNL Smartphone Microscope – Available Technologies – PNNL.

The 3d printer files and links to materials are at the bottom of the page.