Thermal stability of AChE on paper was measured by an investigation at temperatures 4∘ C, 25∘ C, and 37∘ C. For all temperatures, the biosensors were incubated at that specific temperature for 5 minutes after the addition of ATChI solution to the mixture∘of other components. Temperature studies showed that at 4 C the activity of the enzyme ceased and no colour formation was observed. At room temperature and at 37∘C, the yellow colour formation occurred with significantly different colour units with respect to control sensors.