Extended-gate FET biosensor utilizing ionic strength engineering for sensitive prostate-specific antigen detection.

This work presents an extended-gate field-effect transistor (EGFET) biosensor functionalized with prostate-specific antigen (PSA) aptamers. It employs ionic strength engineering to enhance electrostatic coupling and improve detection sensitivity. By systematically adjusting the concentration of phosphate-buffered saline (PBS), we modified the electric double-layer (EDL) structure and Debye length to investigate their effects on charge screening and signal transduction. The proposed biosensor achieved a detection limit of 0.408 ng/mL in 0.001 × PBS, which is significantly lower than the clinical threshold of 4 ng/mL. Additionally, it exhibited an impressive nearly fivefold increase in sensitivity as the ionic strength decreased from 1 × to 0.001 × PBS. These enhancements can be attributed to extended Debye screening and reduced electrostatic shielding in low-ionic environments, facilitating more efficient field-effect coupling between the aptamer-PSA complex and the transistor channel. Temporal noise characterization, conducted through Allan deviation analysis, revealed an optimal averaging range of 30 to 80 s. This range effectively balances noise suppression and signal fidelity. In summary, this study demonstrates a straightforward and effective strategy for regulating ionic strength to enhance the transduction efficiency of BioFET-based biosensors, offering a practical route toward high-performance and label-free PSA biosensing in biomedical diagnostics.