QCM monitoring of macrophage responses to increasing doses of SWCNT. Time and dose-dependent responses of living macrophage based QCM biosensors to varying doses of SWCNTs is shown. In separate experiments, the different doses of SWCNTs were added to the cells after a 24 attachment to the crystal surface. In each case the frequency shift, Δf, was determined from the recorded data and is plotted. This is the frequency difference between that value at the time of addition (arrowhead) and all subsequent times in the QCM response. Macrophage responses to 3 (blue), 10 (grey), 30 (black), 50 (yellow), 100 (navy) and 150 (violet) μg/ml SWCNT exposures are shown. Two control experiments are shown as well: QCM devices with macrophages and vehicle alone (1% BSA) (red); and the QCM, with no cells, responding to the addition of 100 μg/ml (green). In all cases, the frequency response traces represent the average of at least triplicate experiments.