A light detection cell to be used in a micro analysis system for ammonia

This paper describes the design, realization and characterization of a micromachined light detection cell. This light detection cell is designed to meet the specifications needed for a micro total analysis system in which ammonia is converted to indophenol blue. The concentration of indophenol blue is measured in a light detection cell. The light detection cell was created using KOH/IPA etching of silicon. The KOH/IPA etchant was a 31 wt.% potassium hydroxide (KOH) solution with 250 ml isopropyl alcohol (IPA) per 1000 ml H2O added to it. The temperature of the solution was 50 °C. Etching with KOH/IPA results in 45° sidewalls ({110} planes) which can be used for the in- and outcoupling of the light. The internal volume of the realized light detection cell is smaller than 1 μl, enabling measurements on samples in the order of only 1 μl. Measurements were performed on indophenol blue samples in the range of 0.02 to 50 μM. In this range the measurements showed good reproducibility.