When cell biologists need to put DNA inside cells, they have a few basic options, including chemicals, viruses—even a kind of DNA gun. Another option is electroporation, in which a tailored combination of buffer conditions and electrical pulses opens transient pores in the cell membrane, allowing nucleic acids to enter. The technique is probably the easiest DNA-delivery technique there is—just mix DNA and cells in a special cuvette, zap!, and plate. But the technique has downsides, too, including a traditionally high cell mortality rate. Still, for some cells, there’s no substitute. Here are some variables to consider when selecting an electroporation device.
What is your cell type?
There isn’t one single electroporation protocol that works for all cell types. The process needs to be optimized or configured for each experiment. (Electroporation vendors can generally supply starting parameters for a wide array of cell types.)
Before deciding on the best electroporation system, consider the type of cells you are trying to transfect. Are they fragile primary cells or hardy, immortalized cell lines? Are they eukaryotic or prokaryotic? And what about stem cells? Each one requires a different set of conditions.
For instance, according to the Basic Applications Manual for Eppendorf’s Multiporator® system, the “minimum pulse voltages at which the cell membranes may be permeated” can vary widely with cell diameter, from 530 volts for a five-micron cell, at room temperature with a two-millimeter cuvette, to 30 volts for an 80-micron cell. Voltage also varies with temperature, the document says; the five-micron cell that can be permeabilized with 530 volts at room temperature requires 1,100 volts at 4°C.
Whatever your research focus, make sure the system can handle the kinds of cells you anticipate using. For instance, most electroporation devices work only with suspension cells or with adherent cells that have been trypsinized and put into suspension. Some systems, though, including Lonza’s 4D-Nucleofector™ Y Unit module, can transfect adherent cells, too—a gentler option, especially for finicky adherent cells like neurons.
How configurable do you want your system to be?
Electroporation systems can be either “open” or “closed.” Open electroporators—such as Bio-Rad’s Gene Pulser systems—enable the user to configure all settings, such as the pulse length, pulse intensity, waveform and so on. This is the advanced, power-user option—the Linux approach, if you will. Closed systems (e.g., Lonza’s Nucleofector systems), by contrast, cannot be user-configured. These are “black boxes” in which the user selects a pre-designed program (supplied by the manufacturer) and presses “Start.”
What throughput do you need?
All electroporation systems can handle samples one at a time. The most common form uses an electrode-lined cuvette (as in Bio-Rad’s Gene Pulser systems). Life Technologies’ Neon™ system, though, uses a special-purpose metal pipette tip; just suck up the cells in a disposable Neon tip, insert into the Neon Pipette Station and go.
But what if you need to electroporate a whole microtiter plate’s worth of cells? Some systems have optional modules that enable users to transfect an entire plate at once. For instance, the Lonza 96-well Shuttle™ Device is an optional add-on to the 4D-Nucleofector, enabling up to 96 independent programs to run simultaneously. A 384-well alternative (the HT Nucleofector™ System) is also available.
How many cells do you want to transfect?
Electroporation typically requires a relatively large number of cells, because a large fraction of them will not survive the electroporation process. But systems vary in terms of the cell numbers they require. Life Technologies’ Neon tips, for instance, require from 100,000 to five million cells, depending on the protocol and tip size. Lonza’s Nucleocuvette™ strips can handle as few as 20,000 cells. Or, if you want to transfect cells one by one, there is Molecular Devices’ Axon Axoporator® 800A, a patch-clamp system add-on that allows electroporation of individual cells under the microscope with small molecules, proteins or nucleic acids.
What kinds of molecules do you need to deliver?
Finally, consider the types of experiments you want to run. Will you be delivering plasmid DNA or small RNAs? Yeast artificial chromosomes or oligonucleotides? Conditions that work for one type of nucleic acid generally differ from conditions for the other, so some optimization may be required for your specific application.
Optimization is required with all systems
Optimization is a general rule when it comes to electroporation: Whatever you’re doing, be prepared to optimize, optimize, optimize.
The image at the top of the page is from Molecular Devices' Axon Axoporator 800A.