QCM RESPONSE TO SOLVATED, TETHERED MACROMOLECULES

When the quartz crystal microbalance (QCM) is operated in contact with solution and used to detect inertia increases caused by macromolecule s binding to its surface, resonance frequency shifts are reported in t he literature to be greater than, less than, and the same as an identi cal macromolecular mass would cause as a dry layer. A previous report of wet and dry M13 DNA giving the same, linear frequency versus mass r esponse is examined. The M13 data are shown to follow the reciprocal o f the square root of mass, not the reported linear relationship. New e xperiments on RNA duplexes oscillated in solution are reported. A loss y polymer layer is placed between the QCM and RNA. When changes in den sity, viscosity, and included water are eliminated, the response remai ns linear for a constant adlayer thickness. The expectation that respo nse per unit mass should decrease with distance from the QCM surface i s demonstrated, Total decoupling of mass lying beyond the acoustic ove rlayer is also demonstrated. The present results are placed in context with recently published results from a study of progressively thicker protein layers bound to the QCM.