A plug-and-play platform of ratiometric bioluminescent sensors for homogeneous immunoassays

Ni, Yan; Rosier, Bas J. H. M.; van Aalen, Eva A.; Hanckmann, Eva T. L.; Biewenga, Lieuwe; Pistikou, Anna-Maria Makri; Timmermans, Bart; Vu, Chris; Roos, Sophie; Arts, Remco; Li, Wentao; de Greef, Tom F. A.; van Borren, Marcel M. G. J.; van Kuppeveld, Frank J. M.; Bosch, Berend-Jan; Merkx, Maarten

Heterogeneous immunoassays such as ELISA have become indispensable in modern bioanalysis, yet translation into point-of-care assays is hindered by their dependence on external calibration and multiple washing and incubation steps. Here, we introduce RAPPID (Ratiometric Plug-and-Play Immunodiagnostics), a mix-and-measure homogeneous immunoassay platform that combines highly specific antibody-based detection with a ratiometric bioluminescent readout. The concept entails analyte-induced complementation of split NanoLuc luciferase fragments, photoconjugated to an antibody sandwich pair via protein G adapters. Introduction of a calibrator luciferase provides a robust ratiometric signal that allows direct in-sample calibration and quantitative measurements in complex media such as blood plasma. We developed RAPPID sensors that allow low-picomolar detection of several protein biomarkers, anti-drug antibodies, therapeutic antibodies, and both SARS-CoV-2 spike protein and anti-SARS-CoV-2 antibodies. With its easy-to-implement standardized workflow, RAPPID provides an attractive, fast, and low-cost alternative to traditional immunoassays, in an academic setting, in clinical laboratories, and for point-of-care applications.