MIT scientists have demonstrated the possibility to measure dry mass, dry density and water mass of single living cells using a micromechanical resonator.
Manalis group at MIT always performs exceptional researches. Recently, They have presented an inspiring paper on a method for direct non-optical quantification of dry mass, dry density, and water mass content of single living cells in suspension, using a micromechanical resonator known as SMR (Suspended Microchannel Resonator).
SMR was presented for the first time in 2003, in (I definetely consider) seminal paper in the field of biosensing, Burg and Manalis Appl. Phys. Lett. 83, 2698 2003. SMR is an hollow cantilever-like micromechanical resonator that enables the flowing of the samples inside the sensor. In this way, SMR significantly increases the sensitivity by eliminating damping and viscous drag caused by the vibration of the resonator in liquid. SMR detects the mass of the flowing samples by monitoring the resonance frequency shift (as always, harmonic oscillator is everywhere !). This brilliant idea lead to a several of very interesting research in the field of analytical biology.
Manalis group presents a new method for direct quantification of single living cells characteristics by intracellular water exchange. This approach exploits the high water permeability of cellular membranes. They have weighed cells buoyant in H2O and D2O respectively, in this way the acqueos portion of the cell is neutrally buoyant in both measurement since intracellular H2O is replaced by D2O upon immersion in D2O. The paired weighings offer the direct measurement of the cell’s dry mass. In an another configuration, first they measure the buoyant mass in a impemeable fluid as dense as D2O and then in D20, considering that the dry mass content remains the same, they directly measure the intracellular water mass content.
Feijó Delgado F, Cermak N, Hecht VC, Son S, Li Y, et al. (2013) Intracellular Water Exchange for Measuring the Dry Mass, Water Mass and Changes in Chemical Composition of Living Cells. PLoS ONE 8(7): e67590. doi:10.1371/journal.pone.0067590