A novel electrochemical immunosensor that amplifies Poly(o-phenylenediamine) signal by pH-driven cascade reaction used for alpha-foetoprotein detection

• Published in: Analytica chimica acta 2023-01, Vol.1239, p.340647-340647, Article 340647
• Main Authors: Jiang, Mingzhe, Wang, Min, Li, Pengli, Lai, Wenjing, Song, Xuetong, Li, Zhenchao, Li, Jiajia, Li, Hongling, Hong, Chenglin
• Format: Article
• Language: English
• Subjects: alpha-Fetoproteins; Biosensing Techniques - methods; Cascade reaction; Co2+-PDA; Electrochemical Techniques - methods; Gold - chemistry; Hydrogen-Ion Concentration; Immunoassay - methods; Limit of Detection; Metal Nanoparticles - chemistry; pH driven; Poly (o-phenylenediamine); Reproducibility of Results
• ISSN: 0003-2670; 1873-4324
• DOI: 10.1016/j.aca.2022.340647

The present protocol develops an electrochemical immunosensor with poly(o-phenylene diamine) attached gold nanoparticles (PPD@Au NPs) as the immune platform, polydopamine-loaded cobalt ions (Co2+-PDA) as the immune probe, and K2S2O8 as the signal amplifying substance with pH-driven cascade reaction. The application of conventional immunosensors often leads to easy leakage of the current signal and increases the impedance due to assembly. However, this new immunosensor offers the following advantages: (1) The signal substance PPD is modified on the electrode surface, effectively reducing the signal loss and leakage of the immunosensor; (2) The pH response reduces the impedance of the immunosensor while destroying the Co2+-PDA secondary antibody label; (3) The pH response releases a small amount of Co2+, leading to SO4−· generation by K2S2O8 through a cascade reaction, further amplifying the PPD response current signal; (4) The pH response generates excess Co2+ and the by-product PDA fragments can consume the SO4−· generated by K2S2O8, so that the final response signal decreases with the increasing antigen concentration. The experimental results showed that the immunosensor exhibited good selectivity, long-term stability, and reproducibility for AFP detection in the range of 1 pg/mL-100 ng/mL, with a detection limit of 0.214 pg/mL. Interestingly, it is expected to be used for detecting AFP in actual blood samples. •pH response destroys Co2+-PDA secondary antibody label and reduces the impedance of immunosensor.•Co2+-PDA is the first applied to electrochemical immunosensors, can store a large amount of Co2+.•A small amount of Co2+ released by pH response can induce SO4−· production from K2S2O8 through a cascade reaction.•The cascade reaction can further amplify the response current signal of PPD.•The pH response produces excessive Co2+ and by-product PDA fragments can consume SO4−·, making the response signal reduced.