Publication of the week

Week 31 – A research group led by Gabriel Popescu developed a new optical method for measuring growth of individual cells during the cell cycle. Although growth patterns vary within cell populations, knowledge of individual growth is still limited. Optical methods that do measure single cell growth often measure cell volume and assume this is a good indicator for cell mass. The new method called SLIM allows scientists to calculate dry cell mass more directly. The scientists demonstrate the technique for E.coli and U2OS cells in a publication in the early edition of PNAS.

The technology

Spatial light interference microscopy (SLIM) combines phase contrast microscopy with holography. The scientists added a SLIM module with Fourier lenses and a liquid crystal phase modulator to a phase contrast microscope. According to the scientists, the technique results in speckle-free quantitative phase maps. From these phase maps, the dry mass density can be calculated per pixel. A publication in Optics Express in January describes the technique in more detail.

Images

Quantitative dry mass density map of a pair of human osteosarcoma cells acquired using Spatial Light Interference Microscopy (SLIM). SLIM is a non-invasive optical method which may be used to measure the dry mass of single cells with femtogram accuracy. In conjunction with fluorescence microscopy, SLIM can be used to study how a single cells growth rate changes depending on its age and current cell cycle stage.

Images and caption were kindly provided by Gabriel Popescu, assistant professor at the Quantitative Light Imaging Laboratory at the University of Illinois.

Publication

Mir, M., Z. Wang, Z. Shen, M. Bednarz, R. Bashir, I. Golding, S. G. Prasanth and G. Popescu "Optical measurement of cycle-dependent cell growth." Proceedings of the National Academy of Sciences