A method of marker-free examination of biochemical reactions, bonding and/ or attachment processes on/or in at least one thin layer whose thickness is between 0,1 nm und 100 μm, preferably between 10 nm und 2.000 nm, comprising the steps of: - illumination of at least one punctiform or area-measured region of the at least one thin layer with light of at least one light source, - directing that part of the radiation reflected on consecutive boundary surfaces of the at least one thin layer to at least one detector, - detecting of that part of the radiation reflected on consecutive boundary surfaces of the at least one thin layer with the at least one detector, the light incident to the at least one detector being monochromatic, - measurement of the modification of the detected light intensity caused by the change of the optical layer thickness due to the biochemical reactions, bonding and/or attachment processes, - deducting of parameters from the change of the detected light intensity which characterise the reactions, bonding and/or attachment processes on/or in the at least one thin layer, characterised in that one single optimal wavelength is selected for the monochromatic light incident to the at least one detector, wherein - the wavelength most suitable for the examination is selected via experimental measurements by recording a thin-layer spectrum of the thin layer, thereby plotting the light intensity as a function of the wavelength and determining the optimal wavelength in the range of a turning point of the thin-layer spectrum, or - the wavelength most suitable for the examination is selected via theoretical calculation by varying the thickness of a selective layer for a given cover layer and for a given support showing the selective layer with a given refractive index as thin layer, calculating the degree of reflexion for different wavelengths for each layer thickness of the selective layer, plotting it in a diagram against the layer thickness in nm, calculating the derivative of the degree of reflexion with respect to the layer thickness for each wavelength, and determining the optimal wavelength for a given layer thickness as being the wavelength for which by the given layer thickness the derivation has an extremum. - illumination of at least one punctiform or area-measured region of the at least one thin layer with light of at least one light source, - directing that part of the radiation reflected on consecutive boundary surfaces of the at least one thin layer to at least one detector, - detecting of that part of the radiation reflected on consecutive boundary surfaces of the at least one thin layer with the at least one detector, the light incident to the at least one detector being monochromatic, - measurement of the modification of the detected light intensity caused by the change of the optical layer thickness due to the biochemical reactions, bonding and/or attachment processes, - deducting of parameters from the change of the detected light intensity which characterise the reactions, bonding and/or attachment processes on/or in the at least one thin layer, - the wavelength most suitable for the examination is selected via experimental measurements by recording a thin-layer spectrum of the thin layer, thereby plotting the light intensity as a function of the wavelength and determining the optimal wavelength in the range of a turning point of the thin-layer spectrum, or - the wavelength most suitable for the examination is selected via theoretical calculation by varying the thickness of a selective layer for a given cover layer and for a given support showing the selective layer with a given refractive index as thin layer, calculating the degree of reflexion for different wavelengths for each layer thickness of the selective layer, plotting it in a diagram against the layer thickness in nm, calculating the derivative of the degree of reflexion with respect to the layer thickness for each wavelength, and determining the optimal wavelength for a given layer thickness as being the wavelength for which by the given layer thickness the derivation has an extremum.