Non-lethal macrophage phagocytosis measured by QCM. Macrophage living cell QCM biosensors (50,000 cells/QCM) are shown operated at 10 MHz in parallel with control QCMs containing no cells (panels A and B). In experiments using degradable materials represented by Zymosan A (panel A), cells alone (red) and Zymosan A alone (blue trace) showed little change in frequency over 28 hrs, until trypsin cell removals (black arrows) at the termination of the experiment (panel A). Macrophages treated with Zymosan A (black trace) exhibited an increase in oscillation frequency that corresponds to increased migratory behavior by video-microscopy but frequency remains below 200 Hz indicating cells remain attached to the crystal, until trypsin cell removal (black arrow) and cell counting at the termination of the experiment (panel A). Cells are able to take up, degrade and regurgitate Zymosan A and it serves as a model system for macrophage neutralization of particulate material. As an example of macrophage phagocytosis of non-degradable materials, polystyrene beads were also used for testing (panels B and C). In the QCM, beads alone (blue trace) or cells alone (black trace) again led to little change in frequency over the 28 hr time course. In contrast, as living macrophages accumulated intact beads in their cytoplasm, as seen by phase microscopy (panel C), the frequency dropped over the first 12 hrs and then as cells regurgitated the beads, returned to baseline (panel B).