The optION sensor project

The electrolytes sodium, potassium, calcium, chloride and hydrogen ions (the pH value) are essential for the water balance of the human body. In medical diagnostics, the concentration of electrolytes is determined frequently for patients with several illnesses such as kidney diseases, heart failure, alcohol poisoning, diabetes mellitus, and diarrhea. Disorders in electrolyte concentrations can have severe consequences. A too low sodium concentration can lead to a swelling of brain cells which can result in a coma. Preventing this is essential. Especially when treating children, the determination of electrolyte concentrations poses a problem. Drawing a blood sample from these little patients is complicated and the amount of blood obtained is mostly quite small.

State-of-the-art electrolyte analyzers need a separate sensor for every electrolyte. Such a setup requires a certain blood volume (70-80 µL) in order to reach all sensors. The blood sample volume that can be drawn from infants mostly does not suffice for this.

The goal of the "optION sensor" project is to examine a new measuring principle from the field of photonics, which makes the analysis of minimal blood volumes possible. For this, optical microring resonators are utilized. These are light guiding structures with a ring shape through which laser light is conducted. If a substance binds to the surface of the ring resonator, its optical properties are altered. The change of the properties is proportional to the amount of the bound substance. As it is possible to detect slightest changes of the optical properties, minimal amounts of a substance can be detected with a high reliability. The ring resonators are coated with a capture molecule (ionophore) which allows for a specific binding of an electrolyte. By utilizing a microfluidics module, several microrings coated with different ionophores can be used simultaneously to analyze different electrolytes in a blood sample. This allows for a determination of all electrolyte concentrations from blood volumes smaller than 20 µL.