Immunoassays are widely used for detection of antigens in a wide range of applications including assays in pharmaceutical development. Immunoassays are continuously improved in many aspects including automatization, miniaturization and extending the dynamic range. The need to measure low abundance molecules are challenging and the need to improve the sensitivity is desired. The Gyrolab technology is a miniaturized immunoassay performed in an automated system covering a broad concentration range. In order to  extend the sensitivity, the technology is combined with Binding Oligo Ladder Detection (BOLD) amplification. The technology behind BOLD or Exazym ® utilizes a DNA primer, a polymerase, and a template (RNA) to generate a ladder-like modified DNA strand. Antibodies with affinity for the polymerized DNA:RNA hybrid strand (duplex) conjugated with reporter molecules are introduced to the system, resulting in an increased number of signal-generating molecules associated with each bound analyte molecule. In this thesis, the development of an ultra-sensitive immunoassay is pursued by applying Exazym ® add-on reagents to the Gyrolab platform, comparing performance with the standard Gyrolab sandwich assay and other commercially available high-performing TNF-α assays. The work includes characterization of a wide range of reaction variables involved in the BOLD signal amplification process including hybridization, polymerization, and detection of a synthetic oligonucleotide. The breakthrough involves the introduction of Allophycocyanin (APC) as a fluorescent conjugate, significantly improving sensitivity and signal-to-noise ratios. The BOLD amplified sensitivity for the TNF-α assay approaches levels seen in ultra-sensitive biomarker assays like Erenna ® and Simoa®. Exazym® technology on the Gyrolab platform allows highly sensitive biomarker assays with minimal sample volume and a 1–2-hour run-time. The study marks substantial progress in achieving ultra-sensitive biomarker assays on the Gyrolab platform through BOLD signal amplification. The use of APC-conjugated detection reagents holds promise for future optimization studies.

Immunoassays are analytical methods that use the highly specific binding of antibodies in order to detect and quantify an analyte. The technique has become a staple in modern biopharmaceutical research and diagnostics, however the measurement of biomarkers like dysregulated cytokines require ultra-sensitive immunoassays that can detect molecules at sub pg/mL concentrations. One such method is the Exazym® signal amplification. Based on a method called Binding Oligo Ladder Detection (BOLD), it is a set of add-on reagents where a primer is conjugated to a detection antibody which is then combined with a template, polymerase and modified DNA nucleotides to generate a oligonucleotide ladder that is detected with a secondary detection antibody; this amplifies the signal by a factor of 10-100 in an existing immunoassay.  By applying this method to the Gyrolab® microfluidic immunoassay system, a sensitivity increase of 880x-1800x was achieved between a pre-synthesised BOLD product and the polymerised BOLD product. Several key factors for successful polymerisation in the microfluidic system were identified: adding the template separately before the polymerase and using a buffer with low ionic strength for the secondary detection antibody. Applying the BOLD amplification to an existing Gyrolab TNF-α assay only resulted in similar sensitivity as previous methods however. This report demonstrates that BOLD amplification can be successfully performed in a flow-through format on miniaturized affinity columns in the Gyrolab system to increase the sensitivity by orders of magnitude, where both the immunoassay and the amplification steps are automated in the system. However, further optimisation is needed for application in biomarker assays.