Semiconductor Device-Based Sensors for Gas, Chemical, and Biomedical Applications

AlGaN/GaN Sensors for Direct Monitoring of Nerve Cell Response to Inhibitors 21

© 2011 by Taylor & Francis Group, LLC

balanced in the alkaline region. Then the CO

2

concentration in the incubator must be increased. In

this case, the buffer system reacts as follows:

High H

+

level: H

3

O

+

+ HCO

3

−

⇔ H

2

CO

3

+H

2

O ⇔ CO

2

+ 2 H

2

O,

High OH

−

level: OH

−

+ CO

2

⇔ HCO

3

−

Because of the high CO

2

concentration and the presence of sodium hydrogen carbonate in the

milieu, the pH is kept constant as long as the cell cultures are in the incubator. Once the vessel with

cells is removed and exposed to normal atmosphere, which has only 0.3% CO

2

concentration, the

milieu becomes alkaline (i.e., a pH of about 8.5) and changes its color to violet, indicated ...