Method and apparatus using selected superparamagnetic labels for rapid quantification of immunochromatographic tests

Mika PA Laitinen¹, Jari Salmela², Leona Gilbert¹, Risto Kaivola¹, Topi Tikkala², Christian Oker-Blom¹, Jukka Pekola³, Matti Vuento¹

¹Department of Biological and Environmental Science; ²Department of Physics, University of Jyväskylä, Jyväskylä, Finland; ³Low Temperature Laboratory, Helsinki University of Technology, Helsinki, Finland

Abstract: A rapid method and instrumentation for quantification of immunochromatographic tests (ICT) are described. The principle and performance of the method was demonstrated by measuring the levels of human chorionic gonadotropin (hCG) present in urine. The test format was a sandwich assay using two distinct monoclonal antibodies directed against hCG. The first anti-hCG antibody was labeled with superparamagnetic particles whereas the second was immobilized as a narrow detection zone on a porous membrane. The human urine sample was mixed with superparamagnetic particles coated with the first anti-hCG antibody, and the mixture was allowed to migrate past the detection zone containing the second anti-hCG antibody. Capillary forces facilitated migration of the immune complexes along the porous membrane. The amount of superparamagnetic particle-labelled monoclonal anti-hCG bound to the detection zone was directly proportional to the amount of hCG present in the sample as detected by measuring magnetization in the detector coil. The method had a practical detection limit of 20 U/l (54 nM) of hCG per 5 μl of human urine and a linear range of three decades from 20 U/l to 10 000 U/l. In addition, the analysis was completed within less than 10 minutes. Thus, the test format should be suitable for fast detection and monitoring of a large variety of clinically important parameters and analytes.

Keywords: affinity, biosensor, hCG, immunochromatography, magnetization, superparamagnetic