Eppendorf Multiporator - Electroporation - Manual (Page 7)

31
Biophysical basics of the Multiporator's technique
Crucial parameters for successful electroporation are the voltage and the length of the pulse (time constant τ ) used.
Both factors can be set directly on the Multiporator ® . The parameters for major applications can be found in numerous
existing application protocols, available on the Eppendorf homepage at www.eppendorf.com. For a new application,
reference values for the optimal pulse voltage can be calculated or can be taken from the corresponding tables
(see Sections 3.1 and 4.1.4).
Voltage and pulse length
Fig. 1: Controlled exponential decay of the voltage of the microsecond pulse of the Multiporator ®
The pulse voltage is readjusted every 5 µs. After the time constant τ (tau), the pulse voltage has dropped down to 37 %
of its initial value. The initial pulse voltage and the time constant τ are the only parameters which define the microsecond
pulse of the Multiporator ® .
The voltage set on the Multiporator ® corresponds to the initial voltage (V
0
) of the discharge curve shown in Fig. 1. The
time constant ( τ ) shown is the time required for the voltage to decrease to the value V
0
/e (= approximately 37 % of the
initial voltage). For example, if a voltage of 1,000 V and a time constant of 40 µs have been set on the Multiporator ® , the
initial voltage of the Soft Pulses is 1,000 V. After 40 µs, this voltage has decreased to approximately 370 V. After these
40 µs, the electronic control of the Multiporator
® will have regulated the voltage eight times (i.e. at intervals of 5 µs).
Gap width and field strength
Since the strength of an electrical field depends on the distance of the electrodes, the usage of electroporation cuvettes
with a gap width of 1 mm, 2 mm, or 4 mm results in a different field strength (= pulse voltage [V]/gap width [cm]) in the
cuvette. As the 100 µl volume of the 1-mm cuvette is extremely small, electroporation of eukaryotic cells is normally
carried out using cuvettes with a gap width of 2 mm (400 µl) or 4 mm (800 µl). If a voltage of 800 V is set on the
Multiporator
® , a field strength of 2,000 V/cm is produced when a 4-mm cuvette is used. However, if a cuvette with a gap
width of only 1 mm is used at the same setting, the field strength is 8,000 V/cm! For this reason, particular attention must
be paid to the type of cuvette used for the experiments.
5 µs
1000
800
600
400
200
0
0 40 80 120 160 200 [ µs]
[V]
( )
τ
5 µs
37%
2 Principle of the Multiporator®
2 Principle of the Multiporator®
Multipor_Appli_E_poration_en.fm Seite 31 Montag, 30. Januar 2006 2:17 14