Electrochemical Immunosensor Based on Gold Nanoparticles/Polypyrrole-Polydopamine

A novel ultrasensitive impedimetric immunosensor was constructed for the detection of carcino-embryonic antigen (CEA) using conductive and adhesive bio-inspired gold/polypyrrole-polydopamine nanocomposites as an immobilization matrix. A polypyrrole-polydopamine (PPy-PDA) complex was first prepared by the polymerization of pyrrole and dopamine, which was then blended with the chloroauric acid solution (HAuCl₄). The in-situ reduction of \rm AuCl_4^\;\;- to gold nanoparticles (Au NPs) by polydopamine led to the successful preparation of gold/polypyrrole-polydopamine nanocomposites (Au/PPy-PDA). Au/PPy-PDA was characterized by Fourier transmission infrared (FT-IR) spectroscopy, scanning electronic microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX) and electrical conductivity test. The dispersion test and adhesion test showed that PPy-PDA possessed good dispersibility in water and outstanding adhesion performance. The electrochemical measurement showed that Au/PPy-PDA not only provided a highly stable and biocompatible matrix for the convenient conjugation of antibody, but also accelerated the electron transfer process owing to the conductive PPy as well as encapsulated AuNPs, making it suitable to be applied as high-efficiency immunoassay platform. Under optimal conditions, a wide linear range from 10⁻¹² ～5×10⁻⁷ g/mL and a detection limit of 0.2 pg/mL were demonstrated for the detection of CEA. Moreover, the proposed CEA immunosensor exhibited high specificity, excellent stability and reproducibility, providing an experimental evidence for early diagnosis and treatment of cancer.