This article describes a protocol for quantifying alginate concentration using an ELISA-based method. The process involves preparing samples, applying antibodies, and measuring colorimetric changes to determine alginate levels.
Take a microplate with a sample containing alginate, a protective exopolysaccharide produced by the bacterium Pseudomonas aeruginosa.
Prepare a serial dilution of an alginate-derived standard to quantify sample alginate concentration.
Add a coating buffer and incubate to facilitate adherence of the molecules to the well surface.
Wash to remove unbound molecules.
Incubate with a blocking agent to mask non-specific binding sites.
Wash, then incubate with primary antibodies specific to alginate.
Wash again, then incubate with enzyme-conjugated secondary antibodies that target the primary antibodies.
Wash and then incubate with a chromogenic substrate, which the enzyme oxidizes to produce a colored product.
Add an acidic solution that stops the reaction and enhances the color to enable colorimetric detection.
Using a microplate reader, measure the color intensity.
Create a standard curve from the intensities of the standard dilutions and plot the sample intensity to determine alginate concentration.
Using a micropipette, add 50 microliters of the collected sample to an untreated 96-well plate.
Then add 50 microliters of ELISA coating buffer to the wells. Incubate the plate at 37 degrees Celsius for two hours. Using a squirt bottle, wash the plate wells twice with PBS-T by filling the wells and then draining them by flipping the plate over.
Add 200 microliters of blocking buffer to the wells with a micropipette and incubate at four degrees Celsius overnight. The next day, wash the plate twice with PBS-T as before. Then add 100 microliters of diluted primary antibody to the wells and incubate at 37 degrees Celsius for one to two hours.
Following incubation, wash the plate wells three times with PBS-T as before. Next, add 100 microliters of diluted secondary antibody to the wells and incubate at 37 degrees Celsius for one to two hours. After washing the plate again three times, use a micropipette to add 100 microliters of TMB ELISA solution.
Incubate the plate at room temperature for 30 minutes in the dark by placing the plate into a drawer or wrapping in foil. Then add 100 microliters of stop solution. Use a plate reader to measure the OD at 450 nanometers.
Produce a standard curve by measuring the OD450 of serial dilutions of known concentrations of d-mannuronic acid. Repeat the measurements twice and extract a linear equation. Calculate the concentration of the alginate in each sample using the standard curve and divide the alginate concentration from the linear equation by OD600 to obtain the total amount of alginate per OD600.
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