Detection of β-amyloid peptide (1-16) and amyloid precursor protein (APP770) using spectroscopic ellipsometry and QCM techniques: A step forward towards Alzheimers disease diagnostics

A highly sensitive method of spectroscopic ellipsometry in total internal reflection mode (TIRE) was exploited for detecting beta-amyloid peptide (A beta(1-16)) in the direct immune reaction with monoclonal DE2 antibodies (raised against A beta(1-16)) electrostatically immobilised on the surface of gold. A rapid detection of A beta(1-16) in a wide range of concentrations from 5 mu g/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 A beta(1-16) is highly specific with the affinity constant K-D = 1.46 x 10(-8) mol/l. The same DE2 antibodies were utilised for detection of amyloid precursor protein APP(770), a larger protein containing A beta(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. (C) 2010 Elsevier B.V. All rights reserved.