A Compact Printed Circuit Board (PCB)-Based Protein Biosensor System Using an Interdigitated Array Electrode Structure

This study aims to develop a compact printed circuit board (PCB)-based protein immunosensor for protein detection toward point-of-care testing applications. An interdigitated electrode (IDE) structure fabricated using an electroless nickel immersion gold PCB was functionalized with 11-mercaptoundecanoic acid, EDC/NHS, and anti-bovine serum albumin (anti-BSA) for bovine serum albumin-fluorescein isothiocyanate conjugate (BSA-FITC) recognition. A compact impedance measurement circuit based on a lock-in amplifier was designed and integrated with the PCB-based sensor to simplify impedance measurement without requiring a conventional three-electrode electrochemical workstation. The proposed sensor was evaluated using BSA-FITC concentrations ranging from 0.05 to 10 µM. An impedance change exceeding 10% was obtained at 0.1 µM BSA-FITC, while an estimated limit of detection of approximately 35 nM was obtained. The antibody-functionalized sensors showed substantially higher impedance responses than the antibody-omission control, supporting antibody-dependent protein recognition. The combination of PCB-based electrode fabrication, simplified non-faradaic impedance measurement, and compact electronics provides a practical proof-of-concept platform for further development of low-cost and portable protein biosensing systems.