We present a new and fast method for preparation of ultrathin layers of biomolecules on solid substrates and its application as a useful tool for sensing biomolecules in an affinity biosensor. Nonamphiphilic trimethylsilyl ether-cellulose monolayers are used as interfaces to reduce nonspecific interactions between solid surfaces and biomolecules. These films are transferred on optical waveguides by the Langmuir-Blodgett technique. After their stabilization by cleavage of the hydrophobic trimehylsilyl groups, the cellulose films serve as excellent matrixes for the immobilization of proteins at high density. Cyanurchloride serves as a cross-linker between the cellulose layer and the proteins. The activity and biological specificity of these interfaces is controlled by an enzymatic assay and direct sensing by an evanescent wave immunosensor.

The fluorescence-based detection and counting of single protein molecules after specific binding to antibodies at interfaces is presented. A diode laser was used as the excitation source. The unspecific binding at the interface has been reduced to a level of only 0.1% of the maximum signal level. At present, the detection limit of this molecule-counting process is in the range of 10(-17) mol/L, and the dynamic range of the signal corresponds to 7 orders of magnitude of antigen concentration, but these values are not limiting. As a preliminary application in early-stage diagnosis, we have investigated the detection of a single cardiac actin molecule in human plasma, which is of interest in myocardial infarction diagnosis.

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