The EVOM™ Manual is WPI's next-generation manual TEER meter, replacing all previously manufactured WPI manual TEER instruments — including the EVOM3, EVOM2, and MilliCell® ERS-2. Engineered for reliability, repeatability, and ease of use, the EVOM™ Manual delivers improved workflow efficiency and more stable measurements for epithelial and endothelial cell culture research.

At its core, the EVOM™ Manual features automatic 20X sample averaging, a low-noise circuit design for greater resolution, and adjustable fixed measurement currents (2, 4, or 10 μA) to suit a wide range of membrane types. Resistance auto-ranging covers 1 Ω to 100,000 Ω across three selectable current ranges, with fast stabilization on low-level readings under 200 Ω to a resolution of 0.1 Ω. The low-current, low-voltage design prevents metal ion transport and is non-destructive to cells and membranes.

Data collection is seamless — the EVOM™ Manual logs measurements continuously to a USB flash drive in CSV format, date-stamped and ready for direct spreadsheet import. A new Windows® companion application provides a secured mode of data transfer in addition to USB storage. The ergonomic tilt stand reduces glare, while automatic plate indexing supports operation with or without control well subtraction for both resistance and potential difference (PD) measurements. Graphical display of popular well plate formats (6, 12, 24, 96) enables trend analysis at a glance. A footswitch enables hands-free recording during experiments.

Key Features

Low-noise design for greater accuracy and resolution in TEER measurement protocols. Automatic 20X sample averaging for improved stability. Adjustable fixed currents: 2, 4, or 10 μA. Resistance auto-ranging from 1 Ω to 100,000 Ω, plus three fixed current ranges. Fast resistance stabilization for readings under 200 Ω, resolution to 0.1 Ω. Continuous USB data logging (PC, Mac, Linux) with date-stamped CSV output. New Windows® companion app for secured data transfer. Graphical display of 6-, 12-, 24-, and 96-well plate formats. Automatic plate indexing with optional control-well subtraction. Footswitch for hands-free recording. Auto-save and data recovery when battery is low. Upgradable firmware. CE certified.

How It Works

Cell monolayer confluence is determined by measuring an increase or plateau in tissue resistance, detected through the EVOM™ Manual's low AC current circuit and the STX4 electrode. The instrument qualitatively assesses monolayer health and quantitatively measures cell confluence. Because it uses low AC current, electrode metal deposits and adverse tissue effects are avoided — unlike DC current approaches. Resistance readings are unaffected by membrane capacitance or voltage, making the system ideal for permeability, PD, and detailed membrane studies.

What is TEER?

TEER (Trans-Epithelial Electrical Resistance) measures the electrical resistance across a cellular monolayer to quantify barrier integrity. High TEER values indicate a tight, intact monolayer with restricted ion permeability. A decreasing TEER signals compromised barrier function. TEER measurement is routinely used to confirm confluent monolayer formation in transwell culture systems before beginning permeability or drug transport studies.

TEER Value Calculation

TEER is a normalized resistance value per unit area (Ω·cm²). To calculate TEER, multiply the measured resistance by the membrane surface area: 6-well plate (24 mm inserts) 4.53 cm², 12-well plate (12 mm inserts) 1.13 cm², 24-well plate (6.5 mm inserts) 0.33 cm², 96-well plate (4.3 mm inserts) 0.145 cm². Example: a 12 mm insert measuring 565 Ω gives a TEER of 565 × 1.13 = 638.5 Ω·cm².

Applications

Blood-brain barrier transport studies. Lung epithelial tissue research. Intestinal tissue permeability assays. Skin barrier studies. Drug permeability and absorption testing. Toxicity and cytotoxicity screening. Continuous digital monitoring of target membranes. Measure epithelial or endothelial tissues for confluence, TEER, and potential difference.

Compatible Electrodes

The EVOM™ Manual is compatible with the STX4 EVOM™ Electrode with Removable Blades (EVM-EL-03-03-01) for 6 mm inserts — the recommended electrode for use with this instrument. Legacy STX2 and STX3 electrodes are supported via the 99672 EVOM Legacy Adapter (sold separately). ENDOHM chambers for endothelial/epithelial measurement are available in 6, 12, and 24 mm insert sizes (EVM-EL-03-01-01 to -03), and include the EVOM™ Manual cable 99916.

What’s Included

EVOM™ Manual Epithelial Volt Ohm Meter (EVM-MT-03-02), 32 GB USB drive (with Python 3.8 program for continuous monitoring), USB cable (503535), 1000 Ω calibration test resistor kit (99673), AC power cord and charger (803025), and foot switch (13142). Note: The 99672 Legacy Electrode Adapter for STX2/STX3 electrodes is sold separately.

FAQ

What is TEER and why is it measured?

TEER (Trans-Epithelial Electrical Resistance) measures the electrical resistance across a cellular monolayer to assess barrier integrity. A high TEER value indicates a tight, intact cell barrier with restricted ion permeability, while a decreasing TEER signals compromised barrier function. It is widely used in blood-brain barrier research, intestinal tissue studies, lung epithelial studies, drug permeability assays, and toxicity testing.

What does the EVOM™ Manual replace?

The EVOM™ Manual replaces all previous WPI manual TEER meters — including the EVOM3, EVOM2, and MilliCell® ERS-2 — which have been discontinued. It is fully backward-compatible via the 99672 EVOM Legacy Adapter.

What electrode types are compatible with the EVOM™ Manual?

The EVOM™ Manual is compatible with the STX4 EVOM™ Electrode (with replaceable blades), ENDOHM chambers (ENDOHM-6, -12, -24) via the 99916 cable, and legacy STX2/STX3 electrodes via the 99672 adapter. The STX4 electrode is optimized for the EVOM™ Manual and provides the most accurate results.

Does the EVOM™ Manual automatically calculate TEER values?

No — TEER is a normalized value (Ω·cm²) that requires multiplying the measured resistance by the membrane surface area. For example: a 12 mm insert reading 565 Ω × 1.13 cm² = 638.5 Ω·cm². The instrument measures raw resistance; TEER calculation is performed post-measurement.

How is data stored and transferred?

Data is automatically logged to a USB flash drive in CSV format, with date stamps, for direct import into spreadsheets. The latest version also supports a secured Windows® companion application for data transfer. Data is auto-saved when the last well is reached, and auto-recovery protects data when the battery is low.

What current ranges are available and when should I use each?

The EVOM™ Manual offers three fixed current ranges: ±10 μA (0–10,000 Ω), ±4 μA (0–50,000 Ω), and ±2 μA (0–100,000 Ω), plus an auto-ranging mode (1–100,000 Ω). Use lower currents for sensitive or high-resistance membranes, and the 10 μA range for standard confluent monolayers. Auto-ranging is recommended for initial screening.

Why are my EVOM™ Manual readings drifting or unstable?

Drift is most commonly caused by: electrode tips not fully immersed in media, inconsistent fluid temperature, CO₂ loss affecting media pH in open culture environments, or deposits on electrode tips requiring enzymatic cleaning (Tergazyme or Enzol, weekly). Instability is also reduced by keeping the handheld electrode motionless during measurement.

Is the EVOM™ Manual available and supported in Israel?

Yes. The EVOM™ Manual is distributed and supported in Israel by NBT Ltd. Our team provides expert guidance on TEER measurement protocols, electrode selection, and experimental setup for blood-brain barrier, intestinal, and skin tissue models.