Measuring single-cell density
William H. Grover, Andrea K. Bryan, Monica Diez-Silva, Subra Suresh, John M. Higgins, and Scott R. Manalis, Proceedings of the National Academy of Sciences of the United States of America 108 (27), 10992-10996 (2011). Download
We have used a microfluidic mass sensor to measure the density of single living cells. By weighing each cell in two fluids of different densities, our technique measures the single-cell mass, volume, and density of approximately 500 cells per hour with a density precision of 0.001 g/mL. We observe that the intrinsic cell-to-cell variation in density is nearly 100-fold smaller than the mass or volume variation. As a result, we can measure changes in cell density indicative of cellular processes that would be otherwise undetectable by mass or volume measurements. Here we demonstrate this with four examples: identifying P. falciparum malaria-infected erythrocytes in a culture, distinguishing transfused blood cells from a patient’s own blood, identifying irreversibly-sickled cells in a sickle cell patient, and identifying leukemia cells in the early stages of responding to a drug treatment. These demonstrations suggest that the ability to measure single cell density will provide valuable insights into cell state for a wide range of biological processes.
See also the MIT News story “How dense is a cell?”, which includes a short animation I made to explain the density measurement (right). The source code for this animation is also available.
This paper was highlighted in the “In This Issue” feature of PNAS on July 5, 2011.
Thanks to Leiden University’s Cell Observatory for choosing this as their publication of the week.
Thanks to National Institute of General Medical Sciences for featuring this in their Biomedical Beat.