How to implement a selective colorimetric gas sensor with off the shelf components?

Driau C., Fàbrega C., Benito-Altamirano I., Pfeiffer P., Casals O., Li H., Prades J.D. Sensors and Actuators, B: Chemical. Volume 293, August 2019, Pages 41-44. doi.org/10.1016/j.snb.2019.04.117