A Robust Biosensor Based on the Pd-S Bond-Immobilized Peptide toward Antifouling Electrochemical Detection of an Alzheimer's Disease Biomarker in Serum.

Electrochemical biosensing in complex biological media with biosensors constructed through the Au-S bonding remains a challenge due to the biofouling and biothiol interference. We herein developed an antifouling electrochemical biosensor based on the Pd-S bond for detecting the Alzheimer's disease biomarker Aβ1-42. A multifunctional peptide was designed to integrate the anchoring, antifouling, and recognition sequences, and it was immobilized onto the palladium nanoparticle (PdNP)-modified electrode through the Pd-S bond. Comprehensive characterization and density functional theory calculations reveal that the Pd-S bond exhibits a higher binding energy, shorter bond length, and enhanced electron transfer compared to the conventional Au-S bond. The biosensor based on the peptide immobilized through the Pd-S bond demonstrated exceptional antifouling performance in complex biofluids and exhibited high stability to resist biothiol displacement. For the detection of target Aβ1-42, the biosensor exhibited a wide linear range from 0.1 pg mL-1 to 1.0 μg mL-1, with a low detection limit of 0.038 pg mL-1. Moreover, the antifouling biosensor maintained consistent performance in buffer and serum, and clinical validation using human serum samples showed excellent agreement with the commercial ELISA kits, underscoring its accuracy and potential for real sample diagnostics. This work not only establishes a generalizable strategy for constructing stable and antifouling biosensing interfaces but also highlights the promise of Pd-S chemistry in biomolecule immobilization.