Sandwich ELISA protocol with direct detection

Protocol: Sandwich ELISA with direct detection

This is a general procedure for use with the majority of Bio-Rad reagents recommended for indirect sandwich ELISA. In some cases specific recommendations are provided on product datasheets, and these methods should always be used in conjunction with product and batch specific information provided with each vial. Please note that a certain level of technical skill and immunological knowledge is required for the successful design and implementation of these techniques - these are guidelines only and may need to be adjusted for particular applications. 

Reagents

1. Coating Buffer
Na2CO3, 1.5 g
NaHCO3, 2.93 g
Distilled water, 1 liter, pH to 9.6
For an alternative coating buffer use ELISA coating buffer (BUF030)
2. Blocking buffer
Phosphate Buffered Saline (PBS) containing 1% w/v BSA
For an alternative blocking buffer, use either ELISA BSA Block (BUF032), ELISA Ultrablock (BUF033), or ELISA Synblock (BUF034)
3. Wash buffer
Phosphate Buffered Saline (PBS) containing 0.05% v/v Tween®-20
For an alternative wash buffer use ELISA wash buffer (BUF031)
Recommended Substrates and Stop Solutions
TMB Core+ (BUF062), for use with HRP-conjugated antibodies. Stop with 2M H2SO4.
pNPP (BUF044), for use with alkaline phosphatase-conjugated antibodies. Stop with 1M NaOH.

Method

  1. Coat microtiter plate wells with 100 µl of the appropriate coating antibody, at a concentration between 1-10 µg/ml in coating buffer. Cover the plate and incubate overnight at 4°C. Wash the plate 3 times in wash buffer.
  2. Add 150 µl of blocking solution to each well. Incubate for 60 minutes at 37°C. Wash 4 times in wash buffer.
    NB: For most Bio-Rad antibodies this step can be omitted without having any deleterious effects on the results obtained.
  3. Dilute samples and standards in wash buffer and add 100 µl of suitably diluted samples and standards to the relevant wells. Samples or standards should preferably be run in triplicate. Incubate for 90 minutes at 37°C. Wash 3 times in wash buffer.
  4. Add 100 µl of appropriately diluted enzyme-conjugated detection antibody to each well. Incubate for 1 hour at 37°C. Wash 3 times in wash buffer.
  5. Add 100 µl of appropriate substrate solution to each well. Incubate at room temperature (and in the dark if required) for 30 minutes, or until desired color change is attained.
  6. Read absorbance values immediately at the appropriate wavelength or add 50 µl of “stop solution”. Gently tap plate to ensure thorough mixing. Measure absorbance within 30 minutes.