Martínez-Martín, D. et al. Nature 550, 500–505 (2017).

How much does a cell weigh? Determining the mass of single cells is not trivial, as balances that are sensitive in the nanogram range are not readily available. Martínez-Martín et al. developed a balance that can measure the mass of a single cell with an accuracy of a few pictograms. This picobalance consists of a cantilever that oscillates at its natural resonance frequency. The researchers then attach a cell to the cantilever, which changes the resonance frequency; and this change allows them to calculate the change in mass. Using this technology, the researchers demonstrate that the mass of HeLa cells or mouse fibroblasts fluctuates by 12–15 picograms, and that these fluctuations depend on physiological processes such as water exchange and ATP levels. The researchers also study how viral infection influences cellular mass.