How to Measure TEER with EVOM Manual: A Step-by-Step Guide

Electrical resistance is the difficulty materials impose on current passage, measured in ohms (Ω). Resistance depends on material nature, temperature, cross-sectional area, and length. Good conductors have valence electrons weakly attracted to nuclei, facilitating current flow. Insulators have high resistance preventing current passage. Semiconductors have intermediate properties. Resistivity (Ω·m) is resistance of 1m length, 1mm² area at 20°C. Temperature increases resistance in metals but decreases it in semiconductors. Ohm's Law states current is directly proportional to voltage and inversely proportional to resistance: V = I × R. This allows calculating resistance from voltage and current measurements.

Ohm's Law states that current (I) is directly proportional to potential difference (V) across a conductor (V = IR). Resistance (R) is directly proportional to length (L) and inversely proportional to cross-sectional area (A): R = ρ(L/A), where ρ is resistivity. Resistivity is a material property measured in ohm-meters. Conductivity (σ) is the reciprocal of resistivity: σ = 1/ρ, measured in siemens per meter. The cell constant (G* = L/A) relates solution resistance to conductivity. These principles form the foundation for understanding electrical behavior in both metallic conductors and electrolyte solutions.

Ohm's Law (V = I × R) describes the relationship between voltage, current, and resistance in electrical circuits. Voltage is the potential difference driving current flow, measured in volts. Current is the rate of charge flow, measured in amperes. Resistance opposes current flow, measured in ohms. A short circuit occurs when minimal resistance connects a power source, causing dangerously high current that destroys components. Resistors limit current to safe levels for components like LEDs and lamps. Ground (GND) represents a reference point with zero potential, and all other voltages are measured relative to this point.

This segment covers Ohm's Law, which states that voltage equals current multiplied by resistance (V = IR). Students learn to calculate current when voltage and resistance are given by rearranging to I = V/R. The instructor demonstrates multiple examples with different resistance values, including decimal and large resistance values. Students practice decimal division and fraction-to-decimal conversion. The segment emphasizes that resistance is measured in Ohms and that students should be comfortable with various numerical formats.

Electric charge is a scalar, quantized quantity with symbol 'q' and SI unit Coulomb. The fundamental charge of an electron is e = 1.6 × 10^-19 C. Electric current is the rate of flow of electric charges, symbol 'I', measured in Amperes. Conventional current flows from positive to negative terminal, while electrons flow from negative to positive. Ohm's Law states that potential difference across a metallic wire is directly proportional to current flowing through it, provided temperature remains constant. The formula R = V/I defines resistance. Graphically, plotting V on y-axis and I on x-axis gives a straight line with slope equal to resistance. Resistance is directly proportional to voltage and inversely proportional to current. The SI unit of resistance is Ohm (Ω), named after Georg Simon Ohm.

Cell culture inserts are membrane-based devices containing semi-permeable membranes that split the culture chamber into apical and basolateral compartments, enabling cell polarization, co-culturing, and permeability assays. These inserts feature track-etched microporous membranes produced by breaking polymer molecular chains with accelerated noble gas ions to create defined pore channels, which are then chemically etched and treated with air plasma for optimal cell attachment. The quality of these membranes is critical for reproducible cell culture experiments, requiring uniform pore distribution, proper coating, and even welding to the plastic body. Membrane pore size selection depends on the application: 0.4-1 micron for epithelial and endothelial layers, while 3-8 micron sizes are suitable for migration and invasion studies. Clear membranes are preferred for phase contrast microscopy monitoring, while translucent membranes support faster cell growth. These membrane-based systems are widely used to model biological barriers including the blood-brain barrier, intestinal and respiratory epithelia, skin, hepatic and renal epithelia, and placental barrier, as well as for permeability and toxicity testing of drugs, chemicals, and cosmetics.

Millicell® Hanging Inserts enable 2.5D cell culture by providing a permeable membrane that allows cells to access media and nutrients from both apical and basolateral directions, promoting improved cellular growth and physiological relevance compared to traditional 2D plastic plates; proper setup involves peeling the insert from its blister pack, placing it in a cell culture plate with flanges flat and non-overlapping, ensuring even media levels on both sides, and using the apical assist rim for non-contact media exchanges during cellular growth.

This video demonstrates the proper technique for transferring cell culture inserts to experimental wells, including rinsing with endal medium, adding progenitor medium, using sterile tweezers for transfer, removing old medium and discarding it in bleach, and placing the plate in a tissue culture incubator set at 37°C with 5% CO2 to maintain sterility and optimal cell growth conditions.

This phase covers the transition from flask expansion to submerged culture in transwell inserts. Key procedures include: enzymatic dissociation using ACF solution (7-8 min at 37°C); cell counting with trypan blue and hemocytometer; centrifugation at 350g/1200 rpm for 5 min; resuspension in complete medium; seeding at 100,000 cells/cm² in apical compartment with 200 μL medium; adding 500 μL basal medium; performing full medium changes every 2 days until 100% confluence; then airlifting for mucociliary differentiation. Using PET membrane Costar inserts with 0.4 μm pore size achieves optimal differentiated morphology.

Transwell culture provides a 3D-like environment where epithelial cells contact wet layers on both apical (gut interior) and basolateral (blood vessel) sides. Collagen-coated membranes enable proper adhesion, with cells cultured for three weeks at 15% FBS in DMEM/F12 with supplements. Impedance spectroscopy applies alternating current across electrodes to measure electrical resistance. At low frequencies, impedance reflects resistors (tight junctions); at high frequencies, it reflects reactances (capacitance). TEER quantifies tight junction integrity—the electrical resistance caused by tight junction proteins like claudins and occludins. Higher TEER indicates better barrier function.

Aseptic technique in cell culture involves systematic contamination prevention through personal protective equipment (gloves, lab jacket, glasses), thorough biosafety cabinet preparation with IPA cleaning, proper item handling (spraying and wiping fridge items, immediate spill cleanup), and strict pipetting protocols (never pouring, holding caps face-down on cleaned surfaces, avoiding vessel interiors) to maintain sterile conditions and protect cell cultures from microbial contamination.

Proper aseptic technique in cell culture requires working within a biosafety cabinet using laminar airflow, disinfecting all items with 70% ethanol before use, avoiding lateral arm movements to prevent disrupting the air curtain, using single-use pipette tips, and keeping the workspace organized to minimize contamination risks from bacteria, fungi, and mycoplasma.

Aseptic techniques are essential for preventing contamination in cell culture laboratories. A laminar flow hood has three distinct areas: clean space for sterilized equipment, working space for hands and pipettes, and dirty area for waste. Hands must be sterilized with 70% ethanol and gloves worn. Contamination sources include: improperly sterilized equipment, contaminated cell stocks or media, cell culture reagents (serum, amino acids), and personnel with non-sterile hands or contaminated gloves. Common contaminants include viruses (hard to detect), mycoplasma (spreads quickly), bacteria (most common, easily visible), and yeast.

Successful cell culture requires proper laboratory setup with essential equipment including a cell culture hood, incubator, water bath, centrifuge, refrigerator/freezer, hemocytometer, and microscope; maintaining a sterile environment involves opening all materials within the hood, wiping surfaces with 70% ethanol, organizing items systematically (pipettes in front, reagents at back, waste containers in corners), and avoiding breathing or talking into the hood; mammalian cells should be cultured at 37°C with 5-7% CO2 and high humidity, with flasks evenly spaced for proper gas exchange; reagents should be warmed to 37°C for 10-20 minutes but not left excessive time to prevent degradation; daily microscopic examination is essential for monitoring cell health and detecting contamination.

Microorganisms are ubiquitous and omnipresent in nearly every environment. Contamination refers to the introduction of unwanted microorganisms into cultures or laboratory environments. Aseptic technique minimizes contamination of original and newly inoculated cultures while protecting laboratory workers. This technique ensures only intended microorganisms grow in cultures and prevents infection risks to personnel.