Abstract: The present invention provides a method of determining the amount of an optical probe species binding to or releasing from an optical sensor surface characterized in that the determination comprises the steps of: a) determining, at one single wavelength or at more than one wavelength, a physical measurand (xi) that is related to the absorptivity of said probe, b) correlating the value of the measurand to the amount of said optical probe species binding to or releasing from said surface, respectively, wherein the physical measurand (xi) of step a) is a physical measurand in which the contribution from the refractive index is substantially zero. The present invention further provides different uses of a peak width as well as a computer program product and reagent kits for the disclosed methods.

Abstract: The present invention provides a method of determining the amount of an optical probe species binding to or releasing from an optical sensor surface characterized in that the determination comprises the steps of determining at least one physical measurand (x1i) that is related to the refractive index of said probe at one single wavelength or at more than one wavelength, and further comprises determining at least one physical measurand (x2j) that is related to the absorptivity of said probe at one single wavelength or at more than one wavelength, and further correlating the values of said measurands to the amount of said optical probe species binding to or releasing from said surface, respectively. There is also provided methods for calibration of an optical sensor as well as reagent kits and a computer program product.