Abstract: There is provided an optical sensor for analyte molecules in a fluid, method for manufacturing an optical sensor, system and method. An optical sensor comprises a fluidic channel for fluid flow, said fluidic channel having a sensing area comprising receptors for reference molecules and the analyte molecules in the fluid, and the sensor comprises at least one calibration area comprising calibration molecules, and the at least one calibration area and the sensing area are arranged in a reading area of the sensor such that the sensor is capable of generating a sensor response, when the reading area is exposed to stimuli.