Odorant receptors are an excellent example of natural superiority in binding specific small and hydrophobic molecules. Difficulties in expression, isolation and solubilisation of these receptors have been overcome recently by in vitro synthesis and incorporation of receptors into a planar lipid membrane [1,2]. The incorporation density and the mobility of the membrane embedded receptors were analyzed at the single-molecule level by means of image correlation spectroscopy [3,4]. Instead of a confocal scanning microscope for the image acquisition, we used our total internal reflection fluorescence microscope and an ultra-sensitive CCD camera. The non-uniform excitation intensity requested a modification of the image correlation analysis, i.e. a normalization of the image intensity with the excitation intensity distribution
