Label-free detection of clustering of membrane-bound proteins.

We report a new and label-free method to detect and characterize the clustering of membrane-bound proteins and, by extension, the lateral segregation of nanosized particles adsorbed to planar surfaces in liquid environment. The method exploits the contrast between two different mass and surface sensitive detection methods, quartz crystal microbalance with dissipation monitoring and ellipsometry. The time-resolved correlation of both techniques provides insight into subtle changes in the clustering state of surface-bound molecules that is not accessible with either technique alone. A theoretical model can provide quantitative predictions about the size of surface-bound clusters.