Optical biosensor and method of use

A process for the detection of analyte molecules in a sample comprising providing a sensor consisting of a) a solid support,

• b) a single layer or multi-layer Langmuir-Blodgett (LB) film attached to the surface of said support a),
• c) at least one fluorescent dye F.sub.1 which is located in the top layer or in case of a multi-layer Langmuir-Blodgett film, in at least one of the top four layers of the Langmuir-Blodgett film,
• d) a first receptor molecule which is capable of specific binding with said analyte molecule and which is bonded covalently or by absorption in or on the topmost layer of the Langmuir-Blodgett film, and
• e) exposing said sensor to said sample and a mobil fluorescent dye F.sub.2 whose excitation band overlaps sufficiently for an energy transfer with the emission band of said dye F.sub.1 and which
• e1) is covalently bonded to a second receptor molecule which competes with said analyte molecules for specifically binding to said first receptor molecule d) or which
• e2) is covalently bonded to a third receptor molecule which is able to bind to a complex composed of the first receptor molecule d) and said analyte molecule,
• where the second molecule or the complex of the analyte molecule and the third receptor molecule are initially not bound to the Langmuir-Blodgett film,
• and detecting a change in the level of fluorescence energy transfer in response the said exposing step.