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Direct ELISA Protocol

This protocol outlines the procedure for performing direct ELISA methodology. Information includes required reagents, preparation of reagents and the procedure for all steps involved.

Materials

  • Antigen (preferably purified)
  • HRP-Conjugated Primary Antibody
  • Coating Buffer, 0.05 M Carbonate-Bicarbonate, pH 9.6
  • Wash Solution, 50 mM Tris, 0.14 M NaCl, 0.05% Tween 20, pH 8.0
  • Blocking (Postcoat) Solution, 50 mM Tris, 0.14 M NaCl, 1% BSA, pH 8.0
  • Conjugate Diluent, 50 mM Tris, 0.14 M NaCl, 1% BSA, 0.05% Tween 20, pH 8.0
  • Enzyme Substrate, TMB
  • Stop Solution, 0.18 M H2SO4 or other appropriate solution
  • High Protein Binding Microtiter Plate (i.e. Nunc C bottom Immunoplate 96 well, Cat. No. 446612)

Preparation

Bethyl Laboratories ELISA Accessory Kit may be used or prepare the following reagents as specified below.

Coating Buffer

  • 3.7 g Sodium Bicarbonate (NaHCO3)
  • 0.64 g Sodium Carbonate (Na2CO3)
  • 1 L of distilled water

Tris Buffered Saline (TBS)

  • 6.06 g Tris Base
  • 8.2 g NaCl
  • 6.0 ml 6 M HCl
  • 1 L of distilled water

pH should be 7.2 to 7.8, conductivity should be 14,000 to 16,000

Wash Solution

  • 1 L of TBS
  • 5 ml of 10% Tween 20

Blocking (Postcoat) Solution

  • 1 L of TBS
  • 10 g BSA

Conjugate Diluent

  • 1 L of TBS
  • 10 g of BSA
  • 5 ml of 10% Tween 20

0.18 M H2SO4

Stock is 18 M

  • 10 ml of Stock solution
  • 1L distilled water

Procedure

Perform all steps at room temperature.

Coat with Antigen

  1. Dilute the antigen in Coating Buffer to the desired concentration. For purified antigens 1 – 2 mcg/ml is sufficient. For non-purified antigens, optimal concentration needs to be determined. Transfer 100 mcl of diluted antigen to each well.
  2. Incubate coated plate for 60 minutes.
  3. After incubation, aspirate the antigen solution from each well.
  4. Wash each well with Wash Solution as follows:
  5. Fill each well with Wash Solution
  6. Remove Wash Solution by aspiration
  7. Repeat for a total of 3 washes.

Blocking (Postcoat)

  1. Add 200 mcl of Blocking (Postcoat) Solution to each well.
  2. Incubate 30 minutes.
  3. After incubation, remove the Blocking (Postcoat) Solution and wash each well three times.

HRP Conjugated Primary Antibody

  1. Dilute the HRP Conjugate in Conjugate Diluent.
  2. Transfer 100 mcl to each well.
  3. Incubate 60 minutes.
  4. After incubation, remove HRP Conjugate and wash each well 5 times.

Enzyme Substrate Reaction

  1. Prepare the substrate solution according to the manufacturer's recommendation. TMB is highly recommended but OPD or ABTS can be used.
  2. Transfer 100 mcl of substrate solution to each well.
  3. Incubate plate 5 - 30 minutes.
  4. To stop the TMB reaction, apply 100 mcl of 0.18 M H2SO4 to each well. If using another substrate, use the stop solution recommended by manufacturer.
  5. Using a microtiter plate reader, read the plate at the appropriate wavelength for the substrate. (450 nm for TMB)

Note: This procedure is suitable for alkaline phosphatase conjugated antibody. Use an appropriate substrate for alkaline phosphatase