Protein Immobilization on PCB Solder Mask: Toward Low-Cost Biosensing Platforms

This work demonstrates an efficient and reproducible method for the covalent biofunctionalization of epoxy solder mask surfaces on printed circuit boards (PCBs) produced using a conventional manufacturing process, enabling the implementation of capacitive biosensors without the need for any additional PCB fabrication steps and thereby supporting low-cost biosensing applications. Surface activation was achieved using 600 mM 3-mercaptopropionic acid (3-MPA) and 600 mM EDC/NHS, followed by immobilization of 600 µM bovine serum albumin (BSA) as a model protein, achieving spatial variability below 10%. This methodology can be directly applied to other proteins by simply substituting the biomolecule of interest. ATR-FTIR analysis confirmed successful chemical modification through the appearance of characteristic carboxyl and amide bands, while BCA assays verified effective protein attachment. The sensing performance of the functionalized surface was evaluated using electrochemical impedance spectroscopy on interdigitated PCB-based electrodes. A clear decrease in the impedance module was observed at 1 MHz after BSA immobilization and subsequent anti-BSA binding with a variation of 2826 ± 235 Ω and 4214 ± 239 Ω respectively (p < 0.001). Remarkably, anti-BSA was detected at concentrations as low as 10 ppb. These results highlight not only the strong biochemical activity and stability of the modified solder mask surface, but also its potential for scalable, robust, and cost-effective PCB-integrated biosensors for clinical biomarker detection and point-of-care diagnostics, as well as other widespread diagnostic and sensing applications.