Recommended buffers, solutions
Note: Do not use sodium azide in these preparations. Sodium azide inactivates the horseradish peroxidase enzyme.
The BD OptEIA™ Reagent Set B (Cat. No. 550534) containing Coating Buffer, Assay Diluent, Substrate Reagents A and B, Stop Solution and 20X Wash Buffer Concentrate is recommended.
1. Coating Buffer- 0.1 M Sodium Carbonate, pH 9.5; 7.13 g NaHCO3, 1.59 g Na2CO3; q.s. to 1.0 L; pH to 9.5 with 10 N NaOH.
Freshly prepare or use within 7 days of preparation, store at 2- 8°C.
2. Assay Diluent- PBS* with 10% FBS#, pH 7.0. The BD Pharmingen™ Assay Diluent (Cat. No. 555213) is also recommended.
*Phosphate-Buffered Saline: 80.0 g NaCl, 11.6 g Na2HPO4, 2.0 g KH2PO4, 2.0g KCl, q.s. to 10 L; pH to 7.0
#Fetal Bovine Serum: Hyclone Cat. No. SH30088 (heat-inactivated)
Freshly prepare or use within 3 days of preparation, store at 2-8°C.
3. Wash Buffer- PBS* with 0.05% Tween-20. Freshly prepare or use within 3 days of preparation, store at 2-8°C.
4. Substrate Solution- Tetramethylbenzidine (TMB) and Hydrogen Peroxide.
The BD Pharmingen™ TMB Substrate Reagent Set (Cat. No. 555214) is also recommended.
5. Stop Solution - 1 M H3PO4 or 2 N H2SO4
Additional Materials Required
1. 96-well BD Falcon™ ELISA Plates (Cat. No. 353279) are recommended.
2. Microplate reader capable of measuring absorbance at 450 nm
3. Precision pipettes
4. Graduated cylinder, one liter
5. Deionized or distilled water
6. Wash bottle or automated washer
7. Log-log graph paper or automated data reduction
8. Tubes to prepare standard dilutions
9. Laboratory timer
10. Plate sealers or parafilm
Specimen Collection and Handling: Specimens should be clear, non-hemolyzed and non-lipemic.
Cell culture supernatants: Remove any particulate material by centrifugation and assay immediately or store samples at ≤ -20°C. Avoid repeated freeze-thaw cycles.
Serum: Use a serum separator tube and allow samples to clot for 30 minutes, then centrifuge for 10 minutes at 1000 x g. Remove serum and assay immediately or store samples at ≤ -20°C. Avoid repeated freeze-thaw cycles.
Plasma: Collect plasma using citrate, EDTA, or heparin as anticoagulant. Centrifuge for 10 minutes at 1000 x g within 30 minutes of collection. Assay immediately or store samples at ≤ -20°C. Avoid repeated freeze-thaw cycles.
Standards Preparation and Handling
1. Reconstitution: After warming to room temperature, carefully open vial to avoid loss of material. Reconstitute lyophilized Standard with 1.0 mL of deionized water to yield a stock standard. Allow the standard to equilibrate for at least 15 minutes before making dilutions. Vortex gently to mix.
2. Storage/ handling of reconstituted standard: After reconstitution, immediately** aliquot standard stock at 50 µl per vial and freeze at ≤ -70°C for up to 6 months. Do not leave reconstituted standard at room temperature.
**If necessary, store at 2-8°C for up to 8 hr prior to aliquoting/freezing.
3. Standards Preparation for Assay:
a. Prepare a 100 ng/mL standard from the stock standard. Vortex to mix.
b. Add 300 µL Assay Diluent to 6 tubes. Label as 50 ng/mL, 25 ng/mL, 12.5 ng/mL, 6.3 ng/mL, 3.1 ng/mL, and 1.6 ng/mL.
c. Perform serial dilutions by adding 300 µL of each standard to the next tube and vortexing between each transfer. Assay Diluent serves as the zero standard (0 ng/mL).
Recommended Assay Procedure
1. Coat microwells with 100 µL per well of Capture Antibody diluted in Coating Buffer. For recommended antibody coating dilution, see lot-specific Instruction/ Analysis Certificate. Seal plate and incubate overnight at 4°C.
2. Aspirate wells and wash 3 times with ≥ 300 µL/well Wash Buffer. After last wash, invert plate and blot on absorbent paper to remove any residual buffer.
3. Block plates with ≥ 200 µL/well Assay Diluent. Incubate at room temperature (RT) for 1 hour.
4. Aspirate/wash as in step 2.
5. Prepare standard and sample dilutions in Assay Diluent. See "Standards Preparation and Handling".
6. Pipette 100 µL of each standard, sample, and control into appropriate wells. Seal plate and incubate for 2 hours at RT.
7. Aspirate/ wash as in step 2, but with 5 total washes.
8. Add 100 µL of prepared Working Detector (Detection Antibody + SAv-HRP reagent) to each well. Seal plate and incubate for 1 hour at RT.
9. Aspirate/ wash as in step 2, but with 7 total washes. NOTE: In this final wash step, soak wells in wash buffer for 30 seconds to 1 minute for each wash.
10. Add 100 µL of Substrate Solution to each well. Incubate plate (without plate sealer) for 30 minutes RT in the dark.
11. Add 50 µL of Stop Solution to each well.
12. Read absorbance at 450 nm within 30 minutes of stopping reaction. If wavelength correction is available, subtract absorbance 570 nm from absorbance 450 nm.
Assay Procedure Summary
1. Add 100 µL diluted Capture Ab to each well. Incubate overnight at 4°C.
2. Aspirate and wash 3 times.
3. Block plates: 200 µL Assay Diluent to each well. Incubate 1 hr RT.
4. Aspirate and wash 3 times.
5. Add 100 µL standard or sample to each well. Incubate 2 hr RT
6. Aspirate and wash 5 times.
7. Add 100 µL Working Detector (Detection Ab + SAv-HRP) to each well. Incubate 1 hr RT.
8. Aspirate and wash 7 times (with 30 sec to 1 min soaks).
9. Add 100 µL Substrate Solution to each well. Incubate 30 min RT in dark.
10. Add 50 µL Stop Solution to each well. Read at 450 nm within 30 min with λ correction at 570 nm.
Calculation of Results
Calculate the mean absorbance for each set of duplicate standards, controls and samples. Subtract the mean zero standard absorbance from each. Plot the standard curve on log-log graph paper, with IgE concentration on the x-axis and absorbance on the y-axis. Draw the best fit curve through the standard points.
To determine the IgE concentration of the unknowns, find the unknown's mean absorbance value on the y-axis and draw a horizontal line to the standard curve. At the point of intersection, draw a vertical line to the x-axis and read the IgE concentration. If samples were diluted, multiply the IgE concentration by the dilution factor.
Computer data reduction may also be employed, utilizing log-log regression analysis.
Cross Reactivity: The following isotypes were tested in the BD OptEIA. Assay at 2 µg/mL and no cross-reactivity (value ≥ 2 ng/mL) was identified.
Mouse: IgG1, κ; IgG1, λ; Ig2a, κ; IgG2b, κ; IgG2b, λ; IgG3, κ; IgG3, λ; IgM, κ; IgM, λ; IgA, κ