Paper-Based Electrochemical Device Modified with Palladium: Sensor for the Detection of Serotonin and an Immunosensor for the Detection of SOD1

The early and accurate detection of superoxide dismutase 1 (SOD1) and other biomarkers is crucial for the diagnosis and monitoring of neurodegenerative diseases such as amyotrophic lateral sclerosis. This study reports the development of a low-cost paper-based electrochemical sensor for the detection of serotonin (5-HT) and an immunosensor for the detection of SOD1, the potential biomarkers associated with these diseases. The sensor was fabricated using a conductive ink composed of carbon nanotubes and glass varnish onto an office paper substrate, with a palladium electrochemically deposited on the working electrode. To improve the device's stability and water resistance, the paper surface was treated with beeswax, enhancing its hydrophobicity. Cyclic voltammetry was used to observe the electrochemical behavior, with differential pulse voltammetry applied to 5-HT. An analytical calibration curve was generated, with a limit of detection of 0.35 μmol/L for 5-HT, demonstrating a linear range of 7.00-100 μmol/L in PBS. The Pd-modified electrode enabled efficient immobilization of antibodies, facilitating the selective detection of SOD1 via antigen-antibody interactions. Electrochemical impedance spectroscopy was employed for label-free SOD1 quantification, yielding a linear response in the range of 1.0-100 nmol·L^-1 and a limit of detection of 0.72 nmol·L^-1. The proposed electrochemical immunosensor demonstrates high sensitivity, selectivity, and affordability, making it a promising tool for early stage screening of neurodegenerative disease biomarkers in real-world clinical samples.