Medical applications purgatives

Figure 5.3 shows the drain current of PEI/starch functionalized HEMT sensors measured exposed to different CO2 concentration ambients. The measurements were conducted at 108°C and a fixed source-drain bias voltage of 0.5 V. The current increased with the introduction of CO2 gas. This was due to the increase in net positive charges on the gate area, thus inducing electrons in the 2DEG channel. The response to CO2 gas has a wide dynamic range from 0.9% to 40%, as shown in Fig. 5.4. Higher CO2 concentrations were not tested because there is little interest in these for medical-related applications. The response times were in the order of 100 s. The signal decay time was slower than the rise time, and was due to the longer time required to purge CO2 from the test chamber.

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