Effective peroxidase-like activity of a water-solubilized Fe-aminoclay for use in immunoassay

In this study, we developed a colorimetric sensor for the determination of the peroxidase-like activity of Fe-aminoclay, which was used as a novel way of immunoassay for lung cancer was examined. Fe-aminoclay was synthesized by a facile sol-gel reaction under ambient conditions, with both amino sites and Fe surface exposed outside. This Fe-aminoclay, which exhibits strong peroxidase-like activity particularly over a wide pH range, was explored as a robust and rugged replacement of peroxidase enzymes. The peroxidase-like activity of Fe-aminoclay was proved by means of the production of a blue-colored product by 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H₂O₂). This unique activity, in a folic acid-conjugated form, was evaluated for its ability to specifically detect folate receptor-positive A549 cell, which was compared to a human lung normal cell line with lack of the expression of the folate receptor. The chromatic response, which was even detectable by naked eyes, displayed gradational variation, proportional to the number of cells (up to 20,000 cells).