Design of a rapid point-of-care immunoassay : Based on a single-step non-competitive immunoassay with magnetic permeability detection

Abstract: This thesis describes the development of a one-step, specific, cost-effective and rapid in vitro point-of-care immunoassay test based on a unique magnetic immunoassay principle. The principle in question is based on a non-competitive heterogeneous immunoassay in a one-step analysis, relying on magnetic permeability detection. The heterogeneous immunoassay is performed in disposable reagent vials, containing solid phase (antibody conjugated silica microparticles) and a labelling agent (antibody conjugated superparamagnetic nanoparticles) always in suspension. The sample (antigen) is introduced into the reagent vial and mixed, forming a sandwich complex between the conjugated nano- and microparticles. The complex is sedimented to the bottom of the reagent vial, forming a pellet with increased magnetic permeability, and subsequently measured using an inductance-based magnetic permeability detector.As proof-of-principle, an initial analyte target human C-reactive protein (CRP), a cardiac and inflammation marker in whole blood was chosen. The developed magnetic immunoassay system was characterized by a low detection limit and high accuracy. The immunoassay system was further optimized considering assay time and sample volume for better suitability in a point-of-care setting. Additionally, the two-site immunoassay was enhanced for several target analytes and sample media: human albumin, an indicator of kidney malfunction, in undiluted urine, and canine CRP, acute phase marker for identifying inflammation, in whole blood. Finally, the canine CRP assay was further developed, based on studies of the binding kinetics and reaction mechanisms, improving the sensitivity and extending the linear dynamic range, including inclusion of features suitable for point-of-care use.In summary, the designed one step two-site heterogeneous immunoassay system, utilizing magnetic permeability based detection was shown to be a suitable and reliable method for diagnostic measurements and point-of-care use.