A SERS-Based Antibody-Aptamer Sandwich Assay for Extracellular Vesicle-Associated Tau Detection Using Gold Nanoparticles.

Extracellular vesicles (EVs) have emerged as sources of promising, minimally invasive biomarkers for diagnosing and monitoring diseases like Alzheimer's. Using EVs as a source of biomarkers for neurological diseases is highly relevant because they can carry pathogenic proteins, such as tau and amyloid-β, across the blood-brain barrier and can be easily accessed and collected since they are available in almost all biofluids, including blood, urine, and saliva. Here, a bioanalytical antibody-aptamer sandwich assay detection using surface-enhanced Raman spectroscopy (SERS) is developed to quantify the expression of EV-associated tau. Specifically, a gold surface conjugated with antibodies was developed to capture tau protein derived from EVs. Subsequently, adding gold nanoparticles functionalized with SERS probes and aptamers enabled the detection of tau in EVs using SERS. The sensing platform exhibited excellent reproducibility, selectivity, and sensitivity for tau in a broad range of 30 pM-10 nM with a calculated detection limit of 13 pM. Detecting molecular targets within and on the surface of EVs can enable the design of multiplex biosensors for the early diagnosis of multifactorial diseases by simultaneously detecting and quantifying pathogenic proteins, such as amyloid-β and tau in Alzheimer's disease.