Ellipsometric Immunosensor for Detection of Amyloid Precursor Protein with a View of Alzheimer's Disease Diagnostics

Abstract: The detection of amyloid precursor protein isoform 770 (APP770) was achieved with the use of total internal reflection ellipsometry (TIRE) in a direct immunoassay format with DE2 monoclonal antibodies raised against the β amyloid peptide 1-16 (Aβ 1-16) which is a part of APP770. DE2 antibodies were immobilised on the surface of gold by electrostatic binding to a layer of (poly)allylamine hydrochloride (PAH) via an intermediate layer of Protein G molecules. TIRE spectra were recorded after adsorption (binding) of every molecular layer in a sequence of PAH, Protein G, DE2, and APP770. A noticeable increase in the adsorbed layer thickness was obtained upon binding of APP770 molecules from its solution of unknown concentration in Complete Medium, a complex mixture containing other proteins. For a purpose of TIRE biosensor calibration, complementary quartz crystal microbalance (QCM) measurements were utilised and allowed the evaluation of surface concentrations of DE2 and APP770 of 1.08^.10¹¹ cm^-2 and 4.73^.10¹² cm^-2, respectively.

Keywords: Alzheimer's disease, Amyloid precursor protein, Amyloid peptide, Direct immunoassay, Total internal reflection ellipsometry, Quartz crystal microbalance

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1*Alexei Nabok, 1Mohd Kamarulzaki Mustafa, 2David Parkinson, 1Anna Tsargorodskaya

^1*Alexei Nabok, ¹Mohd Kamarulzaki Mustafa, ²David Parkinson, ¹Anna Tsargorodskaya