Standing wave total internal reflection fluorescence microscopy to measure the size of nanostructures in living cells.

We present the first application of standing wave fluorescence microscopy (SWFM) to determine the size of biological nanostructures in living cells. The improved lateral resolution of less than 100 nm enables superior quantification of the size of subcellular structures. We demonstrate the ability of SWFM by measuring the diameter of biological nanotubes (membrane tethers formed between cells). The combination of SWFM with total internal reflection (TIR), referred to as SW-TIRFM, allows additional improvement of axial resolution by selective excitation of fluorescence in a layer of about 100 nm.