Exercise 6.7 - Electrical Properties of Artificial Membranes

LEVEL II

Materials

• Artificial lipid membrane from Exercise 6.6
• KCl electrodes 6
• DC voltage source
• Wheatstone bridge to monitor resistance 7

Procedure

1. Insert a salt bridge connected to standard electrodes and suitable for measuring both resistance and potential differences across the membrane.

2. Measure the resistance of the synthetic membrane by passing a small DC current through the membrane and measuring the drop in voltage.
   If one knows the applied voltage (100-200 mV) and the measured voltage ( mV), the following formula will give the resistance (Ohm's law):

   	R = (E / (E - E)) * R
   where	R is the series resistance
   	E is the calibrated input voltage
   	E is the voltage appearing across the membrane.

3. Calculate the area of the membrane based on the diameter of the drilled hole, and multiply R (measured resistance) by the area of the membrane. This will give a normalized resistance in ohms-cm.

4. Compare your calculated value to the data in Table 6.4.

5. Divide your calculated value by the thickness of the membrane 8 to yield the membrane resistivity or specific resistance.

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