Leveraging self-signal amplifying poly(acrylic acid)/polyaniline electrodes for label-free electrochemical immunoassays in protein biomarker detection

Accurate quantification of specific biomarkers is essential for clinical diagnosis and evaluating therapeutic efficacy. A self-signal-amplifying poly(acrylic acid) (PAA)/polyaniline (PANI) film-modified disposable and cost-effective screen-printed carbon electrode (SPCE) has been developed for constructing new label-free immunosensors targeting two model biomarkers: human immunoglobulin G (IgG) and alpha-fetoprotein (AFP). The electrochemically deposited PAA/PANI film on the SPCE serves a dual function: both a bio-immobilization support and a signal amplifier, enhancing biomarker detection sensitivity and efficiency. The self-signal amplification properties of PANI streamline the detection process. At the same time, the high-density surface carboxyl groups from embedded PAA enable covalent conjugation with capture antibodies (anti-IgG and anti-AFP). Subsequently, antibody-immobilized PAA/PANI film-modified SPCEs, as immunosensors, successfully detect IgG and AFP without the need for external redox probes. The reductions in the electrochemical PANI signals of the immunosensors are linearly proportional to the logarithm of IgG and AFP concentrations. The proposed immunosensors exhibit sufficiently wide ranges of calibration curves from 0.10 to 50 ng mL^-1, with limits of detection of 0.080 ng mL^-1 for IgG and 0.090 ng mL^-1 for AFP. The sensors exhibit satisfactory sensitivity and selectivity, indicating their potential for accurate and reliable detection.