the graphic above shows how a blood sample can be mixed with microbeads that bind to cancerous cells -lrb- labelled a -rrb- .
when these are placed in a clip on module that attaches to a iphone camera -lrb- c -rrb- the microbeads produce distinctive diffraction patterns when they clump around a diseased cell -lrb- top right -rrb- .
the scientists behind the device , based at massachusetts general hospital and harvard medical school .