In the human body, electrolytes play a key role in maintaining water balance and distribution of fluids. All charged particles dissolved in the blood interact with each other. If a disturbance to their complex equilibrium is suspected, the concentration of a variety of these microminerals will be analyzed. Researchers from the Fraunhofer Institute for Telecommunications, Heinrich-Hertz-Institut, HHI and partners from a variety of disciplines have joined forces as part of the optION project. The project goal is to develop a device concept that uses a photonic sensor solution to significantly reduce the amount of blood needed for analysis and make the testing process significantly easier for all those involved.