Effects of flow rate on sensitivity and affinity in flow injection biosensor systems studied by 55-MHz wireless quartz crystal microbalance

In this paper, we developed a 55-MHz wireless-electrodeless quartz crystal microbalance (QCM) and systematically studied the effects of flow rate on the sensitivity to the detection of proteins and on the affinity between biomolecules evaluated by the flow injection system. Brownian motion of proteins in liquid suggests a low probability of meeting, and the convection effect plays an important role in the sensitivity and the affinity in the flow cell injection system. The wireless quartz crystal was isolated in the QCM cell, and flow rates between 50 and 1000 microL/min were used for monitoring binding reactions between human immunoglobulin G and Staphylococcus aureus protein A. The sensitivity was significantly increased as the flow rate increased, while the affinity value remained unchanged. However, the affinity value was affected by the reaction time for a large-concentration analyte, indicating the need of a high-sensitivity biosensor system for accurate evaluation of affinity. The electrode effect on the QCM sensitivity was also theoretically investigated, showing that the electrode significantly deteriorates the QCM sensitivity and makes the Sauerbrey equation invalid.