High-Frequency Wireless and Electrodeless Quartz Crystal Microbalance Developed as Immunosensor

A wireless and electrodeless high-frequency quartz crystal microbalance (QCM) was developed for monitoring biochemical reactions in real time without using any labeling procedures. An analytical vibrational calculation for a multilayered plate showed that the QCM sensitivity significantly deteriorates when metallic electrodes are present on the crystal surfaces, indicating the importance of an electrodeless QCM biosensor. The 30-μm-thick electrodeless QCM immunosensor was excited, and its mechanical vibration was detected contactlessly using an antenna located outside the QCM cells. The homebuilt QCM system was used to detect human immunoglobulin G (hIgG) using staphylococcal protein A (SPA) immobilized on the crystal surface and to demonstrate the higher sensitivity of the electrodeless QCM than that of the conventional QCM. The 30-μm-thick QCM, with a 54MHz fundamental frequency, successfully monitored the hlgG-SPA binding reaction for a hIgG concentration of 100pg/mL.