Abstract: A modular sensor system for continuous measurement of analytes in continuous flow has a fluidic module, a sensor module, an optional reference module, and a cover part which are stacked on top of each other and firmly connected with each other so as to be releasable. The fluidic module includes a fluid duct having an inlet and an outlet. The sensor module includes a sensor compartment which has at least one sensor and is in fluid communication with the fluid duct of the fluidic module. The optional reference module is in fluid communication with the fluid duct of the fluidic module by means of a diaphragm. The cover part seals the sensor module or the reference module.