EVOM

Automated measurement of tissue resistance in cell culture microplates provides the important advantages of speed, precision, decreased opportunity for contamination and the instant availability of measured resistance data on a computer. These measurements are useful in applications such as drug bioavailability studies and studies on the mechanisms of drug transport.

The main components of the REMS AutoSampler include:

• Robotic sampler that moves the electrode over each well of the microplate
• Electrode which is located on the robotic arm
• Base plate for the 24-and 96-well tray
• Windows-based data acquisition card
• REMS interface unit
• REMS software to operate the system on a Windows-based computer

The REMS AutoSampler automates TEER measurements previously made with WPI's EVOM2 Epithelial Voltohmmeter. Automated tissue resistance measurements up to 20kΩ can be performed on 24- or 96-well HTS microplates. Microplates presently supported include the Corning Costar HTS Transwell-24, Falcon HTS Multiwell insert systems, and Millipore Multiscreen™ CaCo 96-well plate. The REMS AutoSampler is designed to facilitate integration with other robotic systems. Special locating bars are installed on the REMS base platform that allow other system robots to place an HTS tray into a precise location on the REMS base.

The REMS AutoSampler automatically measures and records tissue resistance from a user-specified matrix of culture wells on the microplate. According to the specified sequence, the robotic arm moves over the identified wells taking TEER measurements. By means of a x-y-z locating system, the electrode-containing arm is positioned precisely and reproducibly over each well. The ability of the REMS AutoSampler to reproducibly and precisely locate the electrode results in highly reproducible TEER measurements. TEER measurements are stored in the computer as the electrode moves from one well to the next. The Windows-based software provides user-friendly features to acquire, display and store the tissue resistance measurements.

The REMS electrode is compact and robust in design. Each of two rod-shaped probes, 1.5mm in diameter, consists of a pair of electrodes: one electrode for injecting current and the other for measuring the voltage. The use of two pairs of electrodes eliminates the error caused by the electrode-liquid interface. To take a measurement, the robot inserts one probe into the center of the filter well and the other into the opening slot of the 24- or 96-well plate. The use of AC current to measure resistance provides several advantages over DC current, including:

• Absence of offset voltages on measurements
• There is a zero net current being passed through the membrane, and therefore it is not adversely affected by a current charge
• No electrochemical deposition of electrode metal.

The REMS AutoSampler also features a rinse and calibration check station. If occasional rinsing of the REMS electrode is required, it maybe sent to a rinse...more

The EVOM2 measures trans epithelial electrical resistance (TEER) in tissue culture research. The EndOhm series of chambers for the EVOM2 are designed to accurately measure trans endothelial electrical resistance. Learn how to setup your EndOhm Chamber with an EVOM2 Epithelial Volt Ohm Meter. See how to equilibrate the sensors when taking a voltage measurement. And, learn how to take resistance and voltage measurements.

...more

EVOM was the first instrument designed to perform routine Trans Epithelial Electrical Resistance (TEER) measurement in tissue culture research. EVOM2 is the next generation, redesigned for greater usability.

The EVOM2 sports the following features:

• Rechargeable Battery - EVOM2 , which plugs into a standard wall outlet, comes with a NiMH 6V 200mAH rechargeable battery backup. The battery charges whenever the unit is plugged in. If the battery runs low, the EVOM2 automatically shuts down. Simply install the supplied power cord and plug it into the wall outlet. The battery will fully charge in 24 hours. Normal laboratory testing can continue while the EVOM2 recharges.
• Tilt...more

The World Precision Instruments (WPI) EVOM² is used for making trans epithelial electrical resistance (or TEER) measurements. We recommend that you test your EVOM2 before you use it for the first time and then periodically after that. If there is a concern that the meter or the electrode is not functioning properly, test the meter first. This video shows how to test the meter.

More Info

The World Precision Instruments (WPI) EVOM2 is used for making trans epithelial electrical resistance (or TEER) measurements. Two silver/silver chloride pellets are used for the electrodes. The chloride ion tends to migrate, which is a reversible reaction. But, because of this chloride ion swapping, the electrodes need to be polarized before each use. Before using the meter for making voltage measurements, equilibrate the electrodes. This video shows you how.

More Info

A Volt Meter

A volt-ohm meter may apply a constant voltage of unknown current across the membrane and damage the cells electrically and also leave a chemical imbalance in the electrodes. WPI experimented with two volt-ohm meters:

• An expensive Fluke meter applies a DC voltage of 50 to 80mV, which (in a 1000Ω membrane) will pass 80µA. With a 200Ω membrane, this is 400µA.
• A discount meter puts out 500mV DC, which will pass 500µA through the membrane. With a 200Ω membrane, this is 2.5mA.

Volt Meter Charges or Electrocutes Cells

When you use a volt ohm meter to test a cell layer, the Ag/AgCl electrodes accumulate an unbalanced chemical charge. If the cells are not electrocuted in the process, they also accumulate a charge. The unbalanced electrodes can now act as a source of voltage and current that has to be overcome to make an accurate measurement.

If a volt ohm meter was employed in a TEER (Trans Epithelial Electric Resistance)...more