Cadmium ion-doped magnetic poly(styrene-acrylic acid) nanospheres for sensitive electrochemical immunoassay

A novel class of molecular tags, cadmium ion-doped magnetic poly(styrene-acrylic acid) nanospheres (Cd-MPSA), was first synthesized and functionalized with polyclonal rabbit anti-human luteinizing hormone antibodies (PAb2) for highly efficient electrochemical immunoassay of luteinizing hormone (LH). Transmission electron microscope (TEM) and Fourier transform infrared spectroscope (FTIR) were employed to characterize the prepared Cd-MPSA. By using Cd-MPSA-labeled PAb2 as molecular tags, a novel sandwich-type immunoassay protocol was built for determination of LH on monoclonal mouse anti-human luteinizing hormone antibody (MAb1)-functionalized gold electrode. The assay was carried out in pH 5.3 HAc-NaAc buffer solution by square wave voltammetry (SWV). The signal was obtained by the reduction of the doped cadmium ions in the Cd-MPSA. Under optimal conditions, the currents increased with the increasing LH level in the sample, and exhibited a linear range from 0.25 to 240 mIU mL−1 with a detection limit of 0.08 mIU mL−1 LH at 3sB. The precision, reproducibility, and specificity were acceptable. No obvious difference was encountered in the analysis of spiking LH samples into newborn calf serum with the referenced values.

► Cadmium ion-doped magnetic poly(styrene-acrylic acid) nanospheres as molecular tags.
► Enzyme-free electrochemical immunoassay.
► Mediator-free sandwich-type immunoassay.
► Amplification of electrochemical signal and noise reduction.