Nano Lett. doi:10.1021/nl404514e

Credit: JAY GROVES

The physical properties and spatial organization of membranes dictate their function. However, it has been difficult to visualize the spatial organization and to perform physical size measurements within membranes. To overcome these limitations, Caculitan et al. generated a supported membrane embedded with an array of regularly spaced gold nanodots between 40 nm and 180 nm apart. The nanodots create geometric constraints on the movement of proteins within the membrane where movement is blocked if protein clusters are too large to move between individual array nanoparticles. The authors looked at T-cell receptor (TCR) clusters to demonstrate the utility of the nanodot arrays for monitoring the spatial organization of protein clusters. The supported membrane was functionalized with peptide antigen-loaded major histocompatibility complex (pMHC) so that it could interact with TCR on living T cells. Monitoring TCR movement with a fluorescent antibody, the authors found that the 40-nm-spaced nanodot array impeded long-range TCR cluster transport, yet the signaling function was intact, whereas the 171-nm array allowed for unimpeded cluster movement. A panel of experiments where antigen density and nanodot array spacing were both varied revealed that the effective size of TCR clusters varied continuously with antigen density. Functional signaling clusters readily moved through 40-nm-spaced arrays at low antigen density, whereas at high antigen densities, TCR clusters had difficulty moving through 120-nm-spaced arrays. These findings highlight the ability of the supported membrane format to calibrate how TCR size varies with antigen density, which could not be easily determined by other methods.