Single-Cell Resolution—3D Cell Sizing and Health
At the core of the Moxi Z technology is a precise, volumetric (3D) electrical measurement of each cell or particle as it passes through an aperture (Coulter Principle). The resulting output is a high-resolution histogram that provides exact sizing information for each particle as well as a valuable perspective of the culture composition. The accuracy (r2>0.999) and precision of the Moxi Z particle sizing was illustrated through comparison (Figure 1A) of Moxi Z measured diameters of precision calibrated beads with manufacturer-reported values (3.0 µm, 4.17 µm, 5.6 µm, 7.5 µm, 10.1 µm, 15.6 µm, and 25.0 µm diameters). Furthermore the high-resolution histogram (e.g., Figure 1A inset—five bead mixture) demonstrates the size discrimination capabilities of the instrument.
The quality of the sizing information provided by the Moxi Z strongly contrasts with the imprecision inherent in 2D image-based approaches that attempt to estimate cell size using image interpolation. Consequently, the Moxi Z uniquely enables size-based discrimination and analysis of cell sub-populations and a correspondingly more robust means of separating debris counts from cell counts. This degree of information allows researchers to quantitatively monitor and study size-based changes to their cell populations.
The histogram sizing and shape also provides a means of monitoring culture health. One example of this is shown in Figure 1B, highlighting differences in histogram shapes for a healthy Jurkat population (Figure 1B, blue) versus a mix of healthy and heat-killed (60°C for 30 min, followed by overnight incubation at 37°C) Jurkat cells (Figure 1B, red). Increases in counts in the 4–8 µm range of the histogram reflect increased dead cell and debris counts.
The histogram change is quantified as an MPI value, that is a ratio of the core cell population to the total particle population. Changes in the MPI values and histogram shape can additionally uncover potential microbial contamination in cultures through their contributions to smaller particle counts as they colonize/aggregate.
In this regard, the MPI and monitoring of changes in histogram shapes can provide a level of quality control for the cultures by potentially signaling size changes associated with cellular mutations, cell cycle, variations in media composition, or other environmentally induced health changes.