Bio-Rad Gene Pulser Xcell™ Electroporation Systems - Manual (Page 20)

• With the Protocol Detail screen on the LCD display another pulse can be delivered using the same
pulse parameters. To change the pulse conditions, press Enter; the cursor appears in the voltage
parameter value. The parameters may be changed as described above. To save the pulse parameters,
see Section 3.3.6.
• To review previously delivered pulses, see Section 3.8.
3.3.3 Electroporation Specifying Time Constant
See Section 4.1 for a discussion of electroporation using exponential decay. Use the Gene Pulser Xcell
to deliver an exponential decay pulse with a specific time constant as follows.
• From the Home screen (Figure 3.2), press 2 or use the Up or Down Arrow keys to highlight “Time
constant protocol”, then press Enter. The Time Constant Protocol Detail screen appears
(Figure 3.4).
• A sample must be in place to use Gene Pulser Xcell in this mode. The following parameters must
be entered:
Time constant + Voltage
In time constant mode, Gene Pulser Xcell will maximize the parallel resistance (and minimize the capacitance)
in order to maximize the energy delivered to the sample. Therefore, the PC Module is required to deliver pulses
using the high voltage circuit, while both the CE Module and PC Module are needed to deliver pulses using
the low voltage circuit. The set voltage will determine whether the high voltage or the low voltage circuit is to
be used and will limit the range of the capacitance as indicated in Table 3.2. If a voltage is chosen that spans
both the low voltage and high voltage range, the Gene Pulser Xcell will preferentially use the low voltage circuit.
As indicated in Table 3.2, the acceptable values for the time constant are a function of the sample resistance
and the voltage circuit used.
Immediately before delivering a pulse, Gene Pulser Xcell will determine sample resistance to determine
whether a pulse can be delivered using the set parameters of voltage and time constant. If the set time
constant is outside the range by more than 20%, the Gene Pulser Xcell will show a message indicating
the approximate time constant that can be delivered, and ask that you press the pulse button again to
deliver the pulse. To estimate sample resistance using Gene Pulser Xcell, see Section 3.9.
Table 3.2. Ranges of time constants that may be achieved using Gene Pulser Xcell
at several sample resistances.
Sample resistance Time constant range (msec)
LV Circuit* HV Circuit**
20 ohms 0.5 – 65.5 0.2 – 1.0
200 ohms 5.0 – 655 2.0 – 10
>1000 ohms 25 – 3275 10 – 50
* LV Circuit range: 10 – 500 V
** HV Circuit range: 200 – 3000 V
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