For the first characterization sensors
To determine the lowest detectable ozone concentration under the given conditions (room temperature, light activation, low humidity) in another experiment sensors were exposed to a series of increasing ozone concentrations starting at 50 ppb (Fig. 4). There is a difference of two orders of magnitude in the Cy7 NHS ester line resistance for the two particle types (small particle sensor approx. 150 kΩ; large particle sensor approx. 2 kΩ). This can be explained by simple geometrical considerations. Since both sensing layers are prepared onto the same substrate type (same electrode distance of 20 μm) in between the electrodes are 5 times more inter-grain barriers for the small particle layers compared to the large particle layers (Fig. 4, bottom). The response for the highest ozone concentration is in the same order of magnitude (approx. 350) for both particle types (remark: the measurement was conducted with another pair of sensors with slightly different base line resistances and therefore different maximum response values). Again the small particle sensor shows the faster transient behavior.