World Precision Instruments EVOM2 Epithelial Volt-Ohmmeter

Overview

The World Precision Instruments EVOM2 Epithelial Volt-Ohmmeter is a precision-engineered instrument designed for non-invasive, quantitative measurement of transepithelial electrical resistance (TEER) and transendothelial electrical resistance (TEER/TER) in monolayer cultures grown on permeable membrane supports. Operating on a low-frequency (12.5 Hz) alternating current four-electrode principle—two electrodes deliver current while two separate Ag/AgCl sensing electrodes measure voltage drop—the EVOM2 eliminates errors arising from electrode polarization, liquid junction potentials, and faradaic reactions common in DC-based systems. This architecture ensures high reproducibility and long-term stability across repeated measurements, making it suitable for longitudinal monitoring of barrier integrity in epithelial, endothelial, and tumor-derived cell models (e.g., Caco-2, MDCK, hCMEC/D3, Calu-3). Its galvanic isolation circuitry enables safe operation even when connected to mains-powered data acquisition systems, preventing ground-loop interference and protecting sensitive biological preparations from stray currents or electrochemical artifacts.

Key Features

• Galvanically isolated AC measurement system (12.5 Hz) eliminating electrode polarization, net charge transfer, and metal deposition
• Rechargeable lithium-ion battery providing >10 hours of continuous field operation without grounding risk
• 4.5-digit LCD display (range: 1–9,999 Ω) with auto-ranging and polarity indication
• BNC analog output for direct integration with oscilloscopes, DAQ systems, or GLP-compliant data loggers
• STX2 chopstick electrodes (4 mm × 1 mm cross-section) optimized for insertion into standard Transwell®, Corning Costar HTS, Falcon Multiwell, and Millipore Multiscreen™ inserts
• Integrated calibration resistor for daily verification of measurement accuracy (traceable to NIST standards)
• Compact, benchtop-ready design with ergonomic handle and chemical-resistant housing compliant with ISO 13485 manufacturing controls

Sample Compatibility & Compliance

The EVOM2 supports TEER quantification across all standard multiwell formats used in barrier function assays: 6-, 12-, 24-, and 96-well Transwell® systems with polyester or polycarbonate membranes (0.4 µm, 1.0 µm, 3.0 µm pore sizes). It is routinely employed in applications requiring regulatory alignment—including USP , ICH S5(R3), and OECD TG 431—where barrier integrity serves as a critical quality attribute for in vitro absorption/permeability studies. When paired with WPI’s Endohm-12 chamber, the EVOM2 extends its utility to low-resistance endothelial monolayers (<100 Ω·cm²), enabling comparative analysis under GLP- or GMP-aligned workflows. The instrument conforms to CE marking requirements (2014/30/EU EMC Directive, 2011/65/EU RoHS), and its analog output architecture supports 21 CFR Part 11-compliant audit trails when integrated with validated third-party data acquisition software.

Software & Data Management

While the EVOM2 operates as a standalone handheld meter, its BNC output enables seamless connection to PC-based data acquisition platforms including National Instruments LabVIEW, MATLAB Data Acquisition Toolbox, or WPI’s REMS AutoSampler control suite. For automated high-throughput TEER profiling, the EVOM2 serves as the core sensing module within the REMS AutoSampler system—a robotic platform that performs fully programmable, x-y-z coordinated measurements across 24- or 96-well HTS plates. REMS incorporates automated electrode cleaning and calibration stations using synthetic membrane standards (e.g., polyester-backed lipid bilayers), allowing routine verification of system performance prior to each assay run. All acquired resistance values are timestamped, geotagged (if applicable), and stored in CSV or HDF5 format to support FAIR data principles and retrospective audit readiness.

Applications

• Quantitative assessment of epithelial/endothelial monolayer confluence and barrier maturation kinetics
• In vitro drug permeability screening (e.g., Caco-2, MDCK-II) per FDA guidance on biopharmaceutics classification
• Toxicity evaluation of nanomaterials, surfactants, or inflammatory cytokines on tight junction integrity
• Validation of organ-on-chip microphysiological systems (MPS) under dynamic flow conditions
• Quality control of primary cell isolates and iPSC-derived epithelial lineages during differentiation protocols
• Supporting mechanistic studies of claudin/occludin modulation via siRNA, CRISPR knockout, or pharmacological inhibitors

FAQ

What is the measurement principle used by the EVOM2?
The EVOM2 employs a 12.5 Hz AC four-electrode method: two outer electrodes pass current across the monolayer while two inner Ag/AgCl electrodes measure the resulting voltage gradient—eliminating interfacial impedance artifacts.
Can the EVOM2 measure transendothelial resistance (TER)?
Yes—when used with the Endohm-12 chamber or low-resistance Transwell® inserts, the EVOM2 accurately resolves TER values down to ~5 Ω·cm² with ±2% full-scale repeatability.
Is the STX2 electrode compatible with 96-well HTS plates?
Yes—the 4 mm width and tapered tip allow unobstructed insertion into Corning Costar HTS Transwell-96 and Millipore Multiscreen™ CaCo plates without cross-well contact.
Does the EVOM2 require periodic recalibration?
No—its solid-state circuitry is drift-free; however, daily verification using the supplied calibration resistor is recommended per ISO/IEC 17025 quality assurance protocols.
How does the EVOM2 integrate with automated systems like REMS?
Via its isolated BNC output, the EVOM2 feeds real-time resistance values to the REMS interface unit, which synchronizes electrode positioning, data logging, and automated cleaning cycles under Windows-based scheduling.