Reflection-based sensor for gaseous ammonia

In this work we describe the fabrication of an ammonia sensor on anodized aluminum substrate. Pure aluminum was oxidized with direct current (DC) method at different voltages to obtain oxide layers with different porosity. The adsorption capacities of the differently prepared layers were measured. Bromophenol blue (BPB), bromocresol green (BCG) and bromocresol purple (BCP) indicators were immobilized by simple adsorption. Sensor properties, such as detection limit (100 ppb, 5 and 50 ppm for BPB, BCG and BCP, respectively), dynamic range (0–80, 10–90, 100–600 ppm for BPB, BCG and BCP, respectively), response time and reversibility were investigated. We found, that sensors prepared on different oxide layers with the same indicator, show different signal change in the presence of the same concentration of ammonia gas. Sensors with optimal performance were selected for solving different tasks.