An Optoelectronic Tongue for Simultaneous Detection of β-Amyloid40 and β-Amyloid42

Alzheimer’s disease (AD) is an irreversible, progressive and multifaceted neurodegenerative disorder accompanied by deposition of extracellular amyloid plaques. The main component of amyloid deposits and senile plaques is an aggregated peptide called β-amyloid peptide (Aβ) [1]. Although many details of the AD pathology remain unknown, three biomarkers in cerebrospinal fluid (CSF) including Aβ1-42 (Aβ42), total tau (t-tau) proteins, and p-tau (phosphorylated tau) protein are established biomarkers for AD. Due to the low level of Aβ42 monomers in plasma, the use of Aβ42 to Aβ40 (Aβ1-40) ratio amplifies the difference between AD and normal plasma [2]. Thus, the development of a specific but inexpensive method for simultaneous detection of Aβ42 and Aβ40 (and consequently Aβ42 to Aβ40 ratio) is of great importance.One strategy to move from specific lock-and-key sensors and approach predetermined aim could be the use of ‘nanoparticle (NP)-based optical sensor array’ [3]. In a sensor array, instead of focusing on individual signals, the response from all the sensor elements which exhibit various interaction towards different analytes are collected. Plasmonic NPs exhibit unique and tunable photophysical features due to the localized surface plasmon resonance (LSPR). LSPR depends on shape, size and interparticle distance of NPs and the refractive index of the surrounding medium. There have been great studies in terms of utilizing this dependence as the basis for the development of plasmonic sensor elements [3].In the present study, we developed a ‘nanoparticle-based colorimetric sensor array’ utilizing label-free gold and silver nanoparticles for visual detection of Aβ42 and Aβ40. Different aggregation behaviors of nanoparticles through the conjugation of nanoparticles with Aβ42 and Aβ40 and then the coordination of Aβ42 and Aβ40 with Cu(II) led to diverse spectral and color changes. The spectral changes were quantitatively differentiated by supervised pattern recognition method, linear discriminant analysis (LDA). The proposed sensor was able to discriminate among Aβ42, Aβ40, and HSA in different concentrations (50 nmol L-1 to 500 nmol L-1), as well as mixtures of them with an identification accuracy of 100%. Moreover, the sensor array had the capability to identify structurally similar Aβ peptides in plasma samples.