An ELISA for the determination of human IgG based on the formation of a colored iron(II) complex and photometric or visual read-out

The paper describes a colorimetric sandwich enzyme-linked immunosorbent assay (ELISA) for the determination of human IgG. It is based on the use of an Fe(II) coordination complex as a signal amplifier and of mesoporous silica nanoparticles modified with glucose oxidase (GOx) and secondary antibodies (Ab2). After formation of the immuno sandwich complex, the quantity of GOx is proportional to the quantity of IgG. On addition of Fe(II) and glucose, GOx catalyzes the oxidation of glucose to produce hydrogen peroxide which oxidizes Fe(II) to Fe(III). After adding a stop solution containing the complexing ligand 1,10-phenanthroline (Phen), un-reacted Fe(II) forms an orange-red complex with Phen which can be detected by plate reader and even seen with bare eyes. This sandwich ELISA has a linear response in the 1 pg.mL−1 to 100 ng.mL−1 human IgG concentration range and a 860 fg.mL−1 detection limit. This is 20 times lower than the commercial ELISA for human IgG. The assay also is selective, stable, highly sensitive and cost-effective.