Doubling the quality factor of cantilevers in liquid through fluid coupling-based actuation

Dynamic-mode cantilevers are a promising tool for real-time biosensing applications due to their high sensitivity and ability to perform label-free measurements. However, operating dynamic-mode cantilevers in liquid is challenging since viscous damping greatly reduces their quality factor and thus the limit of detection. We reasoned through physical analysis that if the motion of the surrounding fluid is driven by an external force and not by the sensing cantilever itself, then the dissipative fluid force on the cantilever could be reduced and the quality factor of the cantilever could be increased. Here, we demonstrate a new fluid coupling-based actuation method, where one piezoelectric cantilever (directly excited) is used to excite another closely located cantilever (indirectly excited) through vibrations transferred through the surrounding medium. We performed the measurements in several mediums, including air, water, ethanol, and acetone, and observed that the viscosity of the medium influences the effectiveness of fluid coupling-based actuation. We also observed that fluid coupling-based actuation is more effective for the first bending mode of the cantilever, likely since fluid motion decays with distance from the tip of the directly excited cantilever. A significant result is that the indirectly excited cantilever has a quality factor that is double that of the directly excited one for the first bending mode in water. This method could improve the performance of dynamic-mode cantilevers operated in liquid. Published by AIP Publishing.