Types of Western Blotting Equipment (Cells & Power Supplies)

The tank transfer systems offered by Bio-Rad are described below, and their specifications are summarized in the table below. Selection of the appropriate system is largely dictated by the gel format used for separation and the desired throughput.

Tank transfer systems contain the following elements:

• Buffer tank and lid — the buffer tank and lid combine to fully enclose the inner chamber during electrophoresis. On the inside, the tank has slots for placement of the electrode cards, gel holder cassettes, and cooling element. Ports on the lid allow connection points for the electrodes and are energized using an external power supply
• Gel holder cassette — the gel and membrane sandwich is held together between two foam pad and filter paper sheets, and placed into the tank within a gel holder cassette. Cassettes are made of non-conductive material and designed to permit unimpeded flow of current and buffer through the gel and membrane sandwich
• Electrodes — tank transfer systems use either plate or wire electrode cards. Plate electrodes offer greater field strength than wire electrodes but wire electrodes may be more economical and generate less heat
• Cooling mechanism — cooling systems consist of an ice block, a sealed ice unit, or a cooling coil that is coupled to an external cooling mechanism. These cooling systems prevent temperature fluctuations and overheating during high-intensity, extended, or native protein transfers

Mini Trans-Blot^® Cell and Criterion™ Blotter
The Mini Trans-Blot cell and the Criterion Blotter accommodate mini- and midi-format gels, respectively. The Mini Trans-Blot cell can transfer up to two mini gels (10 x 7.5 cm) in an hour and is available either as a complete apparatus or as a module that uses the buffer tank and lid of the Mini-PROTEAN^® Tetra cell for operation. A self-contained Bio-Ice™ cooling unit absorbs the heat generated during transfer.

The Criterion Blotter can transfer up to two Criterion gels (15 x 9.4 cm) or four mini gels simultaneously in 30–60 min. Temperature regulation during transfer can be achieved through the use of a sealed ice-block or optimal cooling coil.

Trans-Blot^® Cell
The Trans-Blot cell offers a choice of plate or wire electrodes and variable placement of the electrodes for either standard or high-intensity blotting options. The Trans-Blot cell accommodates three gel holder cassettes, each with a 16 x 20 cm blotting area. This system is best for transfer of large-format gels or multiple mini- or midi-format gels. Standard field transfers are performed with the electrodes placed 8 cm apart; with this arrangement, all three of the gel holder cassettes can be used simultaneously. High-intensity transfers can be performed with the electrodes placed 4 cm apart, with a single gel holder cassette between them. Temperature regulation can be achieved using the super cooling coil (included) and a refrigerated water recirculator (purchased separately).

Trans-Blot^® Plus Cell
With a 28 x 26.5 cm blotting area, the Trans-Blot Plus cell has the capacity to transfer three large-format gels or multiple smaller format gels simultaneously in as little as 15–30 min. Adjustable plate electrodes provide a strong and uniform electrical field — up to three gel cassettes can be placed in the tank with the minimum electrode distance between them, increasing the field strength and transfer efficiency. A cooling coil coupled to a refrigerated water recirculator provides temperature regulation.

Specifications for Bio-Rad's tank blotting cells.

Semi-dry transfer generally allows faster transfer and is more economical than tank blotting as it uses a smaller volume of buffer. Semi-dry systems do not offer external cooling.

Specifications for Bio-Rad's semi-dry blotting cells.

Trans-Blot^® SD Semi-Dry Cell
The Trans-Blot SD semi-dry cell performs electrophoretic transfers in 15-60 min. Plate electrodes and a single-step locking system make assembly easy and ensure uniform contact across the entire electrode surface.

Trans-Blot^® Turbo™ Transfer System
The Trans-Blot Turbo system perform semi-dry transfers in as little as 3 min. Turbo transfers are achieved using prepackaged transfer packs containing a nitrocellulose or PVDF (polyvinylidene difluoride) membrane and filter paper stacks pre-wetted with a proprietary buffer. The system can also perform traditional semi-dry transfers with standard filter papers, membrane, and Towbin buffer. The base unit contains an integrated power supply that drives two independent transfer cassettes, allowing maximum throughput of four mini-format or two midi-format gels.

The Bio-Dot^® and Bio-Dot^® SF microfiltration units provide reproducible methods for binding proteins or nucleic acids in solution onto membranes. Once samples are loaded into the wells of the templates, proteins are trapped on the membrane by either vacuum or gravity flow filtration. All subsequent incubation, wash, and detection steps may be performed without removing the membrane from the unit.

The 96-well Bio-Dot apparatus performs traditional dot-blot comparisons, and the 48-well Bio-Dot SF apparatus focuses the applied samples into thin lines instead of circles, which makes it easier to use a densitometer for quantitation. Both sample templates are interchangeable and use the same microfiltration manifold. Both apparatuses are available as a complete unit containing the microfiltration manifold and sample template, or as a modular template without the manifold base.

The Bio-Dot and Bio-Dot SF units can be easily sterilized by autoclaving or by washing in alcohol or sodium hydroxide. The units feature a unique, patented sealing gasket that eliminates lateral leakage and possible cross-contamination among wells. Additionally, sample templates are spaced similarly to microplates, allowing samples to be applied with a standard or multi-channel pipet.

Specifications for Bio-Rad's Bio-Dot microfiltration units.

Electrophoretic transfer cells require high currents that not all power supplies are equipped to deliver. The two Bio-Rad power supplies below are designed to accommodate the needs of electrophoretic transfer systems.

PowerPac™ HC Power Supply
The PowerPac HC (high current) power supply is capable of driving all transfer cells to their maximum performance. The PowerPac HC power supply offers high power output along with the flexibility of choosing transfer under constant voltage, constant current, or constant power settings. The PowerPac HC power supply also offers highly regulated voltage settings, fine adjustment of current limits, and a convenient pause function. Safety features include overload/short circuit detection, automatic crossover, arc and ground leak detection, programmable multi-step methods, and a programmable timer.

PowerPac™ Universal Power Supply
The PowerPac Universal power supply is designed to drive all of the most common electrophoretic applications, with the exception of high-voltage applications such as isoelectric focusing and DNA sequencing. Like the PowerPac HC power supply, the PowerPac Universal power supply provides the choice of transfer under constant voltage, constant current or constant power settings with all of the other features listed above. In addition, the PowerPac Universal stores up to nine methods, each with up to nine steps, and is equipped to enable wireless transfer of run data and protocols for instrument validation for regulatory purposes (for example, installation qualification and operational qualification, or IQ/OQ).

Specifications for PowerPac™ HC and PowerPac™ Universal power supplies.

For more information on power/running conditions, see Performing Electrophoresis section.