Measuring single-cell density using serial suspended microchannel resonators

Abstract

Cells adjust their composition during important physiological processes, including cell cycle progression, apoptosis, and disease. Due to differences in the densities of water and the various macromolecules which compose cells, changes in cellular composition are reflected by changes in cell density. Previously, methods have been described for measuring density at the single-cell level using suspended microchannel resonators by weighing the same cell in fluids of different densities. Here we describe a high-throughput version of this approach, in which cells are weighed sequentially in three cantilevers containing fluids of different densities. The system design and operation are described, measurement uncertainty is characterized, and single-cell density measurements are compared to those obtained using existing techniques. As a demonstration, we use the system to characterize the biophysical response of CD8' T cells during activation. We find that single-cell density distinguishes between the phenotypically distinct human CD8' T cells of healthy vs. chronic lymphocytic leukemia donors, suggesting possible utility as a lymphocyte transformation assay. In summary, the system as described is capable of measuring single-cell density with improved throughput, and the approaches used here for on-chip fluid exchange are applicable to other SMR devices where it is desirable to weigh a cell in multiple fluids, e.g., to measure single-cell growth rate before and after drug or media perturbations..