Gold nanoparticle accumulation using magnetic particles: A new strategy for electrochemical immunoassay based on the reversible reaction between dethiobiotin and avidin

A new method based on accumulation of gold nanoparticles using magnetic particles has been proposed for determining human IgG by anodic stripping voltammetry. The feasibility of the approach was investigated for a noncompetitive heterogeneous immunoassay of human immunoglobulin G as a model. Goat anti human IgG is immobilized on the wells of microtiter plates. The human IgG analyte is first captured by the primary antibody and then sandwiched by secondary antibody labeled with dethiobiotin. The conjugate of biotin modified magnetic particles captured avidin functionalized gold nanoparticles (avidin-Au) was introduced to react with dethiobiotinylated antibody followed by adding of bioitin solution to wash it down. The dissociation of the conjugates from the dethiobiotinylated antibody was caused by displacing function of biotin to dethiobiotin. Making use of the ability of the modified magnetic particles capturing avidin-Au, the following treatment with biotin solutions could realize release of the conjugates for gold ASV quantification. The experiment performed with a blank solution without addition of the analyte showed a low background which is a distinguished advantage providing a possibility for determination of at least 0.1 ng/ml human IgG.