Preliminary Development of a Hybrid Aptamer and Antibody Fluorescent Lateral Flow Assay for Ultrasensitive Detection of Tau441 Protein in Serum: Toward Point-of-Care Diagnostics for Alzheimer's Disease.

A hybrid DNA aptamer and antibody-Europium nanoparticle (Eu NP) fluorescent sandwich lateral flow (LF) assay for Tau441 is described which works well in human serum with an apparent visible detection limit for Tau 441 of ~ 10 pg/ml or 1 pg of Tau protein. The same LF assay appears to detect phosphorylated threonine 217 Tau 441 (phospho Thr-217 Tau) consistently to an even lower level of 1 pg/ml or 100 fg of total phosphorylated Tau protein in human serum. The aptamer was designed in silico on the Xelari computational platform to target an epitope centered around alanine 390 distal from the threonine 217 phosphorylation site, thus the monoclonal antibody must account for the possibly greater affinity for the phosphorylated protein on the other side of the target molecule. Regardless, the hybrid receptor pair exhibits a relatively linear dynamic range of 10 ng/ml to 10 or 1 pg/ml in serum as assessed by visual detection with a high degree of specificity as demonstrated by low cross-reactivity versus other germane human protein targets in buffer, laying the groundwork for a potential rapid and convenient point-of-care (POC) diagnostic for Alzheimer's disease.