An extremely sensitive imaging method that uses two light beams to quantitatively measure cell mass with femtogram accuracy has proven able to track the growth of a single cell and even intracellular mass transport. Developed at the University of Illinois (Champaign, IL), the approach—called spatial light interference microscopy (SLIM)—offers a key advantage over other methods: It can measure all types of cells, from bacteria and single cells to populations (including mammalian, adherent, and nonadherent cells)—all the while maintaining sensitivity and quantitative information derived, according to Mustafa Mir, a first author on a paper describing the work.1
Because of SLIM’s sensitivity, the researchers were able to monitor growth through different phases. Doing so enabled them to discover that mammalian cells exhibit exponential growth only during the G2 phase of the cell cycle—that is, following DNA replication and before cell division—which has implications not only for basic biology, but also for diagnostics, drug development, and tissue engineering. The researchers hope to apply their new knowledge to different disease models: For example, they aim to learn how growth varies between healthy and cancerous cells, and the effects of treatments on growth rates.
SLIM combines holography and phase-contrast microscopy, and requires no staining or other special preparation. Based on white light, it can be combined with more traditional microscopy techniques, such as fluorescence. Mir explains that the method works as an add-on to a commercial microscope: “Biologists can use all their old tricks and just add our module on top,” he says.
1. M. Mir et al., PNAS 108, 32, 13124–13129 (2011).
