A competitive immunochromatographic strip assay for 17-α-hydroxy progesterone using colloidal gold nanoparticles

A rapid and competitive immunochromatographic strip (ICS) test has been developed using colloidal gold as nanoprobe for measuring 17-α-hydroxy progesterone in serum which is a marker for congenital adrenal hyperplasia, an inborn error of metabolism.

Colloidal gold nanoparticles (NPs) were prepared by reducing chloroauric acid with sodium citrate. The corresponding protein conjugate was prepared by passive adsorption of 17-α-hydroxy progesterone-3-carboxymethyl-bovine serum albumin (17-OHP-3-CMO-BSA) immunogen on the colloidal gold surface. Both colloidal gold and its protein conjugates were characterized using standard techniques like transmission electron microscopy (TEM) and atomic force microscopy (AFM) in addition to the optical characterization. The test line antibody was raised against 17-α-hydroxy progesterone-BSA immunogen and control line antibody was raised against BSA in New Zealand white rabbits.

This test antibody showed high immunoreactivity and specificity when characterized by ELISA for 17-α-hydroxy progesterone on microtiter plate. The primary antibody was coated on the nitrocellulose membrane as test line and anti-BSA antibody was coated as control line. The ICS test was developed in competitive assay format. The sensitivity of the present immunochromatographic strip assay was reported to be 2.5 μg/l by visual observation. The signal at the test line was easily readable to the naked eye even at higher concentrations of 17-α-hydroxy progesterone normally associated with congenital adrenal hyperplasia.

The present immunoassay takes 15 min for completion. There has not been any other lateral flow immunoassay for 17-α-hydroxy progesterone reported.