Detection of β-amyloid peptide (1–16) and amyloid precursor protein (APP 770) using spectroscopic ellipsometry and QCM techniques: A step forward towards Alzheimers disease diagnostics

Abstract

A highly sensitive method of spectroscopic ellipsometry in total internal reflection mode (TIRE) was exploited for detecting β-amyloid peptide (Aβ 1–16) in the direct immune reaction with monoclonal DE2 antibodies (raised against Aβ 1–16) electrostatically immobilised on the surface of gold. A rapid detection of Aβ 1–16 in a wide range of concentrations from 5 μg/ml down to 0.05 ng/ml was achieved using a cost-effective and label-free direct immunoassay format. TIRE dynamic spectral measurements proved that the immune reaction between DE2 monoclonal antibodies and Aβ 1–16 is highly specific with the affinity constant K D = 1.46 × 10 −8 mol/l . The same DE2 antibodies were utilised for detection of amyloid precursor protein APP 770, a larger protein containing Aβ 1–16 domain, using the quartz crystal microbalance (QCM) measurements in liquid. A combination of QCM and TIRE kinetics results allowed the evaluation of the originally unknown concentration of APP 770 in complete medium solution containing other proteins, salts, and amino acids.