Electrochemiluminescence Immunosensor for Alpha-Fetoprotein Based on Polypyrrole-Luminol Nanoparticles

The study of luminol electrochemiluminescence (ECL) is commonly conducted in alkaline solutions. However, many substances, especially biomolecules, are only stable in neutral or weakly acidic media. In this study, a sensitive ECL immunosensor was developed using polypyrrole-luminol (PPY-Lu) nanoparticles for the determination of alpha-fetoprotein (AFP) in a neutral buffer. Polypyrrole (PPY) nanoparticles were synthesized by chemical oxidation. Subsequently, luminol was attached to the PPY nanoparticles via electrostatic interaction, resulting in the formation of the desired nanoparticles which exhibited strong and stable electrochemiluminescence in neutral solution. Furthermore, the PPY-Lu nanoparticles have abundant amino groups suitable for immobilizing biomolecules. An ECL immunosensor for AFP was fabricated by immobilizing anti-AFP on the PPY-Lu-modified electrode surface. The electrochemiluminescence decreased when AFP was captured. The immunosensor exhibited a linear range from 1.0 × 10−11 to 1.0 × 10−6 mg/mL with a low detection limit of 8.5 × 10−12 mg/mL and excellent specificity, reproducibility, and long-term stability. This designed immunosensor provides a new method for the determination of biomarkers in clinical analysis.