  Surface molecules, distributed in diverse patterns and clusters on cell
membranes, influence vital functions of living cells. It is therefore important
to understand their molecular surface organisation under different
physiological and pathological conditions. Here, we present a model-free,
quantitative method to determine the distribution of cell surface molecules
based on TIRF illumination and super-resolution optical fluctuation imaging
(SOFI). This SOFI-based approach is robust towards single emitter
multiple-blinking events, high labelling densities and high blinking rates. In
SOFI, the molecular density is not based on counting events, but results as an
intrinsic property due to the correlation of the intensity fluctuations. The
effectiveness and robustness of the method was validated using simulated data,
as well as experimental data investigating the impact of palmitoylation on CD4
protein nanoscale distribution in the plasma membrane of resting T cells.
