Novel instrumentation monitoring in situ platelet adhesivity with a quartz crystal microbalance

The quartz crystal microbalance (QCM) in a solution is capable of sensing an extremely small mass change in the nanogram range. In this article, the authors attempted to apply QCM to in situ continuous monitoring of platelet adhesion in plasma. The instrumentation consisted of a piezoelectric quartz crystal vacuum-deposited with gold and connected to two electrodes, an oscillation circuit, a frequency counter, and a DC source (5 V), coupled with a personal computer, a television monitor, and a printer. The authors noted resonant frequency shifts to determine weight increase upon cell adhesion. A QCM sensor, with the sensitivity of 1 ng/Hz, was placed horizontally in platelet poor plasma. The authors did not observe any measurable frequency shift upon adding a suspension of non-adherent cells, such as red blood cells and prostaglandin I2-sensitized platelets, indicating that QCM does not count the increase in the mass of cells that simply settled on the quartz. They did observe, however, a time-dependent frequency shift upon addition of platelet rich plasma. Coupled with visual determination of numbers of adherent platelets and their morphology under scanning electron microscopy, they found that the magnitude of shift and its time dependence seem to correlate not only numbers of adherent platelets, but to their spreading state, indicating that QCM detects only the weight at the focal contact region of adherent cells. This suggested that the former contributes to the early phase of the frequency shift, and the latter contributes to a shift change after a longer period of incubation.