Optimal Biofunctionalization of Gold Nanoislands for Electrochemical Detection of Soluble Programmed Death Ligand 1

Soluble programmed death ligand-1 (sPD-L1), a pivotal immune checkpoint protein, serves as a biomarker for evaluating the efficacy of cancer therapies. Aptamers, as highly stable and specific recognition elements, play an essential role in emerging point-of-care diagnostic technologies. Yet, crucial advancements rely on engineering the intricate interaction between aptamers and sensor substrates to achieve specificity and signal enhancement. Here, a comprehensive physicochemical characterization and performance optimization of a sPD-L1 aptamer-based biosensor by a complementary set of state-of-the-art methodologies is presented, including atomic force microscopy-based infrared spectroscopy and high-resolution transmission electron microscopy, providing critical insights on the surface coverage and binding mechanism. The optimal nanoaptasensors detect sPD-L1 across a wide concentration range (from am to μm) with a detection limit of 0.76 am in both buffer and mouse serum samples. These findings, demonstrating superior selectivity, reproducibility, and stability, pave the way for engineering miniaturized point-of-care and portable biosensors for cancer diagnostics.