Added Mass Effect on Immobilizations of Proteins on a 27 MHz Quartz Crystal Microbalance in Aqueous Solution

摘要

During the immobilization process of proteins onto an Ausurface of a 27 MHz quartz crystal microbalance (QCM) in aqueous solutions, apparent large frequency changes ((DELTA)F_(water)) were observed compared with those in the air phase ((DELTA)F_(air)) due to the interaction with surrounding water of proteins. On the basis of an energy-transfer model for the QCM, the apparent added mass in the aqueous solution [(-(DELTA)F_(water))/(-(DELTA)F_(air)) - 1] could be explained by frictional forces at the interface of proteins with aqueous solutions. When [(-(DELTA)F_(water))/(-(DELTA)F_(air)) - 1] values for various proteins were plotted against values relating to the friction (antimobility), such as values of the molecular weight divided by the sedimentation coefficient (Mw/s), the inverse of the diffusion coefficient (1/D), and the volume divided by the surface area (volume/surface area velence apparent radius) of proteins, there were good linear correlations. Thus, observations of the larger (DELTA)F_(water) than (DELTA)F_(air) for protein immobilizations on the QCM can be simply explained by the friction effect at the interface between proteins and the aqueous solution. Thus, QCM would be a mass sensor based on mechanical oscillation motion even in aqueous solutions.