Determination of Immunoglobulin G by a Hemin–Manganese(IV) Oxide-Labeled Enzyme-linked Immunosorbent Assay

ABSTRACT An enzyme-linked immunosorbent assay (ELISA) is reported for human immunoglobulin G based on synthesized hemin–MnO2 nanocomposite as the label. Enhanced sensitivity was obtained due to the increased catalytic activity of the hemin–MnO2 nanocomposite toward 3,3′,5,5′-tetramethylbenzidine compared to hemin and MnO2 alone. The synthesized hemin–MnO2 nanocomposite was characterized by transmission electron microscopy and its catalytic activity to 3,3′,5,5′-tetramethylbenzidine was investigated by ultraviolet–visible absorption spectroscopy. After assembly of the sandwich-type immunoassay in the 96 wells of the plate the hemin–MnO2-based label catalyzed 3,3′,5,5′-tetramethylbenzidine into blue compounds that were monitored by a plate reader. The absorbance increased with the concentration of human immunoglobulin G. The immunoassay displayed high sensitivity, a long linear dynamic range, and good selectivity for human immunoglobulin G. The immunoassay was also used for the determination of human immunoglobulin G in serum with favorable results. The developed assay combines the high throughput and low cost of ELISA with the simplicity of nanocomposite labeling and is suitable for application in clinical diagnosis.