The specific recognition reaction between cholera toxin (ChTo) and the ganglioside GM1 was investigated in situ on planar supported lipid layers using simultaneous surface plasmon resonance (SPR) and electrochem. impedance measurements. The lipid monolayers contg. different amts. of GM1 were formed on alkanethiol-coated gold surfaces by a new lipid/detergent diln. technique. The formation of the layers was investigated using both SPR and impedance measurements. While the optical properties of the different lipid layers remained unchanged, the layer capacitance was seen to depend on the GM1 to POPC molar ratio. The selective binding of ChTo to these layers was detected with high sensitivity by SPR. The comparatively small impedance changes assocd. with the protein adsorption suggest a high water content of the ChTo layers. The B5 subunit interacts similarly with these supported lipid layers. [on SciFinder (R)]