Capture the Tag: Mitigation of Biotin Interference in ELISA and Automated Immunoassays by Pre-Conjugating Biotinylated Antibodies to the Streptavidin Surface
Authors: Nelson Heather , Doyle Kelly , Laulu Sonia , Lu Jun 
Published: October 2021

Abstract

Introduction
Streptavidin to biotin binding is one of the strongest non-covalent interactions in nature, and is therefore, successfully incorporated into many immunoassays to facilitate antibody capture. Biotin-streptavidin coupling assays are susceptible to interference from free biotin in patient specimens, which may falsely decrease or increase the result depending on assay format. Currently, biotin-stripping methods capture free biotin in patient specimens by pre-incubation with streptavidin-coated microparticles. However, this approach increases turnaround time, test cost, and testing steps, which increases the chance of error. Our objective was to determine if pre-conjugating biotinylated antibodies to the assay’s streptavidin solid surface before adding patient specimen could mitigate biotin interference in ELISA and automated sandwich immunoassays.

Methods
We performed this study on 3 different ELISAs (CYFRA-21, NSE, S100B) and one automated assay (thyroglobulin); all are a sandwich immunoassay format. Serum pools were spiked with biotin (25 - 1000 µg/L) or PBS control. Manufacturer protocols were followed in both the ELISAs and automated assay to evaluate baseline concentration-dependent biotin interference. Mitigation of biotin interference by pre-incubation was then evaluated in the ELISAs by adding biotinylated antibody to the streptavidin-coated wells 0, 10, 15, or 60 min before adding biotin- or PBS-spiked serum specimens. For the automated assay, streptavidin-coated beads and biotinylated antibody were removed from the reagent cartridge, mixed, and incubated 4.5 hours. The mixture containing biotin-tagged antibody bound to streptavidin beads was added back to the cartridge and placed on the analyzer to evaluate spiked specimens. Lastly, we compared the pre-incubation method to a standard biotin-stripping protocol in the ELISAs to compare the effectiveness of mitigating biotin interference.

Results
We observed biotin interference across the three ELISAs, where 400 µg/L biotin spiked in serum pools reduced analyte detection to between 10 – 15% of the total activity using the standard assay format. Our time-course studies showed 84 – 95% recovery of the total activity when the biotinylated antibody was pre-incubated in the streptavidin-coated wells for 1 hour prior to addition of serum specimens, compared to 69 – 99% by a standard biotin stripping protocol. We extended this concept to the automated immunoassay where at 1000 µg/L biotin in the specimen, only 9 ±0.01% of the total analyte was measured by the conventional method. However, pre-mixing biotinylated antibody and streptavidin beads resulted in 97 ±0.01% of the total analyte recovery in the presence of 1000 µg/L biotin.

Conclusion
We have demonstrated that pre-conjugating the biotin antibody to streptavidin is as effective as biotin-stripping methods to avoid biotin interference in sandwich immunoassays that utilize the biotin-streptavidin system, with the additional benefit of optimizing turnaround times, cost, and labor. A simple change in manufacturer assay design could make immunoassays more robust against biotin interference in patient samples.