Where Standard ELISA Runs Out
You run the assay twice. The result sits just above the noise floor — technically a signal, but not one you’d stake a conclusion on. You dilute the sample and run it again. Same result. Closing the gap between what’s in the sample and what your assay can confidently report is the job of ELISA signal amplification.
BOLD (Binding Oligo Ladder Detection) is Cavidi’s take on it, now peer-reviewed and published in SLAS Technology.
The paper, Reverse Transcriptase Mediated Signal Amplification in Ligand Binding Assays (Nordal et al., SLAS Technology, 2026), is open access, no subscription required.
What the Team Set Out to Do
The question was whether oligonucleotide-labeled antibodies could serve as primers in a reverse transcriptase (RT) reaction to amplify immunoassay signal, without temperature cycling, without anything above 37°C, and using only standard lab equipment. The method adds a single amplification step after the detection antibody binds: the oligo-dT primer on the antibody initiates synthesis of a BrdU-labeled DNA strand, which is then detected by an anti-BrdU antibody. Signal multiplies without touching the capture step, the antibody pair, or the plate reader.
The appeal, and the reason Exazym® is built on this mechanism, is accessibility. Labs don’t need new equipment, new workflows, or new antibody pairs. The amplification step fits into what’s already there.
Several variables were explored systematically. Primer length turned out to be counterintuitive: signal improved from odT18 through odT22 to odT30, then dropped when it went further, to odT40. There’s an optimum, and the data puts it at odT30, with linearity confirmed at R² > 0.99. For anyone developing a custom conjugate, that’s a published starting point rather than a parameter to characterize from scratch.
The SARS-CoV-2 Head-to-Head
The benchmark experiment compared a standard ELISA for SARS-CoV-2 spike protein against the BOLD-amplified version of the same test. Same capture and detector antibody pair, same concentrations, same plate, same HRP readout. The only real difference is the amplification step. As Figure 7 in the published paper shows, it lets the BOLD version stay quantifiable at far lower sample amounts (down to 7.2 × 10⁻¹⁹ mol) than the standard ELISA (4.8 × 10⁻¹⁷ mol).
In that comparison, BOLD detected spike protein at concentrations 67 times lower than the standard version. Because everything else was held constant, the 67× reflects the amplification step alone.
For context, across applications of Exazym® reagent kits, researchers typically see 10–50× sensitivity improvement depending on the assay, with gains up to 200× in optimal conditions. The peer-reviewed 67× sits right in that range.
What’s Next
The paper closes by noting that work is ongoing for other biomarkers, with cytokines and p-tau already producing promising results. That work is what Exazym® StreptaClick® Primer and Exazym® ClickChem Conjugation Kit are built on: the ready-to-use commercial kits that bring this published method into your lab. The point is making that level of sensitivity accessible to any lab, without specialized equipment or extensive reoptimization.
The paper is open access.
Explore Exazym® reagent kits →
We’ll be at ADLM 2026 in Anaheim, July 26–30, at Booth 3679. If you’re working on a low-abundance biomarker detection challenge and want to talk about what Exazym® can do in your context, come find us. Or reach out any time at support@cavidi.se.