We measured the separation of cell membranes from a surface of silica with nanometer precision taking advantage of the fluorescence of an organic dye in the standing modes of light above silicon. For neural cells from rat brain we found about 105 nm on a surface coated with laminin and about 60 nm with fibronectin. No plaques of close adhesion were seen within a lateral resolution of 400 nm. The wide homogeneous cleft raises the question about the nature of the attractive and repulsive forces in cell adhesion.

• Received 8 July 1998

DOI:https://doi.org/10.1103/PhysRevLett.81.5241