25
2. A platinum wire is used as additional reference electrodes. When a platinum wire is gripped with a ground wire with a
bagworm clip of the MED Connector, the platinum wire functions as an additional reference electrode. The reference electrodes
of the MED Probe are positioned at 4 points, and this additional reference electrode of the platinum wire further reduce the
total impedance of the reference electrodes and reduce the noise from the perfusion pump and the stimulation artifact.
Note: Make sure that the platinum wire is fully immersed in the perfusion solution (electrolyte) to conduct with the reference
electrodes of the MED Probe, and that it is gripped by a ground wire with a bagworm clip. If the platinum wire is open, it
serves as antennas that collect electric noise and cause noise.
Reducing a stimulation artifact by a platinum wire. Examples without (left panel) and with (right panel) a MED perfusion cap
6.2.4. Stimulus intensity and electrolysis
As described in the above section, the stimulation current is charged in the electrical double layer capacity and causes voltage Vc
(see figure below). When the voltage Vc exceeds 1 V, the electrodes induce electrolysis and discharge H
2
. This causes a marked
decrease in stimulation efficiency and a marked expansion of the stimulation artifact, and it damages cells and the electrodes.
Therefore, it is essential to prevent a decomposition voltage by stimulation current (Is).
Vc is defined as Vc＝Is × T / Ce. A 50 x 50 µm electrode of the MED Probe has a 50,000 pF capacitance (Ce) (22,000 pF for 20×20
µm electrode). Up to 0.2 ms width (1 phase 0.1 ms) is acceptable for a 200 µA stimulation current.
Note: Do not apply a stimulation intensity and pulse duration width spanning to outside of the shaded area in the figure below.
The numerical values in the graph are based on a “single pulse stimulation.” When a multiple pulse stimulation is applied at
a short inter-stimulation interval of less than 1 s, reduce the stimulation intensity and pulse duration to 80% of the value
shown in the graph.
0.1 ms
(T)
0.2 V
1 V
Electrolytic potential
Vc by 100 µA current
Vc by 500 µA current
Vc: Voltage applied to Ce
Is: Stimulator output current
T: Pulse duration
Ce: Double layer capacitance
Summary of Contents for MED64-Entry
Page 1: ...MED64 Entry Manual ...
