Sandwich ELISA test that requires two distinct epitopes located distantly is not suitable for small molecules like Indoxyl sulfate (IS) as they have limited number of distinct epitopes and cannot be captured by two different antibodies simultaneously. Therefore, Leadgene’s Indoxyl Sulfate (IS) ELISA kit employs a competitive ELISA test over the commonly used sandwich ELISA tests.
The IS concentration standard curve (Fig. 1), for Leadgene's IS mb ELISA kit, is constructed by plotting the percentage bound (B/B0) of known samples with varying IS concentrations. The standard curve functions to quantify IS concentration in unknown samples.
Fig 1. Leadgene's IS mAb ELISA standard curve
L-Tryptophan, 3-Indoleacetic acid and Indole are small molecules that have similar molecular structures to IS as they are a family of pyrrole derivatives. Hence, they will produce false-positive results by binding to detection antibodies with low specificity. In addition, these molecules are commonly present in blood serum samples as they are involved either during upstream or downstream IS synthesis, further increasing the chances of non-specific binding.
Fig. 2 proves that the addition of similar molecules (Tryptophan, 3-Indoleacetic acid and Indole) does not compete with the IS antigens for our IS mAb recognition sites, signifying that our IS mAb is highly specific. This prevents false positive results as our IS mAb does not recognize non-specific molecules.