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In the past decade the quartz crystal microbalance with dissipation monitoring technique (QCM-D) has emerged as a powerful biosensor technique. A key feature of the technique is that the shift of the resonant frequency obtained upon adsorption of mass on the QCM-D sensor surface includes both the actual mass and liquid (water) associated with it. For a rigid film containing no water (low dissipation shifts), the frequency shift can be considered proportional to the mass of the film. For viscoelastic films containing water (high dissipation shifts), however, it is difficult to determine how much of the frequency shift results from the actual adsorbed mass and how much is entrapped or associated water. In some applications, the signal enhancement that is obtained through the associated liquid, makes the QCM-D technique unique with respect to the added information that is gained compared to for example optical techniques. In particular, spontaneous fusion of lipid vesicles onto solid supports have been studied extensively using the QCM-D technique, and unique new information has been obtained. However, for a full picture one would, for such complex viscoelastic films, ideally want to combine the QCM-D technique with a technique that allows separation between the adsorbed (dry) mass and the associated liquid. This presentation shows a new such instrument combining directly, on one and the same surface, QCM-D and reflectometry. Both the experimental set-up and new results obtained with it are described. |