BIOMEMS. Class V. Ion Selective Electrodes. Dr. Marc Madou. Ion selective electrodes (ISE’s) and CO 2 sensor (examples of potentiometric sensors) Oxygen sensor (based on the fuel cell principle) Enzyme based glucose sensor (amperometric) and urea (potentiometric)
Class V. Ion Selective Electrodes
Dr. Marc Madou
Ion selective electrodes (ISE’s) and CO2 sensor (examples of potentiometric sensors)
Oxygen sensor (based on the fuel cell principle)
Enzyme based glucose sensor (amperometric) and urea (potentiometric)
From ISFET to ISN’t FET (potentiometric)
Often reference and glass electrode are combined in one single structure (How would you make such a thing ? See homework Q 1)
The resistance (impedance) of this sensor is very high (glass layer) so that the input amplifier of the pH meter must be very high (the input impedance of the meter must be at least 100 > than that of the sensor!)
Very high impedance can make the measurement noisy. The smaller the sensor the bigger this problem becomes.
Ion selective electrodes (ISE’s)
Carbon dioxide sensor
"Fuel cell" oxygen sensors consist of a diffusion barrier, a sensing electrode (cathode) made of a noble metal such as gold or silver, and a working electrode made of a metal such as lead or zinc immersed in a basic electrolyt (such as a solution of potassium hydroxide).
Oxygen diffusing into the sensor is reduced to hydroxyl ions at the cathode:
O2 + 2H2O + 4e- -------- 4 OH-
Hydroxyl ions in turn oxidize the lead (or zinc) anode:
2Pb + 4OH- ------------- 2PbO + 2H2O + 4e-
2Pb + O2 ----------------- 2PbO
Fuel cell oxygen sensors are current generators. The amount of current generated is proportional to the amount of oxygen consumed (Faraday's Law).
+ 0.6 V
Design a combination glass electrode. Explain how it works.
Design a planar immunosensor. How could you incorporate a good reference?
Explain how a potentiometric CO2 sensor works.
List a list of reasons why the ISFET did not become a commercial success.