An Impedimetric Micro-Immunosensing Assay for the Detection of Alzheimer’s Disease Biomarker

Alzheimer’s disease (AD) is characterized behaviourally by progressive memory and cognitive decline and physiologically by the presence of two established pathophysiological hallmarks in the brains that are extracellular accumulations of amyloidbeta peptide (Aβ) and intracellular neurofibrillar tangles of hyper phosphorylated tau protein [1,2]. Studies claimed that Aβ is generated by the sequential cleavage of amyloid precursor protein (APP) resulting in the production of variable lengths of Aβ. The two major forms of Aβ that have been observed to be produced under normal conditions of APP processing are 40 and 42 residues in length (Aβ40 and Aβ42, respectively) [3-5]. In a normal individual, Aβ40 is the most abundant Aβ species present in human brain and such fragment could, however, also undergo an aggregation process [6]. Aβ40 in its aggregated form is found to be one of the major components of toxicity [7], and presence in insoluble plaques are detected in brains of AD patients and induces behavioural effects on some types of memory dysfunction [8]. Currently, enzyme-linked immunoassays (ELISA) are still one of the most prevalent sensing platforms for the detection of trace amounts of Aβ protein. However, even though it was such a reliable analytical tool but ELISA system is time consuming in which it requires 4–6 h to complete and its dependence on labelled bio reagents may lead to a decrease in assay sensitivity due to reduced biomolecular activities [9-11]. In this context, a rapid, label-free immunosensing technique would offer an irresistibly attractive option for overcoming this problem [12]. Here, an impedimetric immunosensing assay, based on the integration of specific surface antibodies as a biorecognition element and an impedimetric signal transducer for Aβ detection has been developed The use of impedimetric signal transducer in biological sensorial application is based on the premise that an interaction between biological receptor and its target species recruited from the solution caused a change in the interfacial charge transfer kinetics between the electrolyte and electrode site. This type of assay has inherent specificity and selectivity provided by antibody-antigen bio specific interaction on electrode surfaces as well as advantages offered by the impedimetric-based biosensing technology, such as label-free detection capability, high sensitivity, cost-effectiveness in mass production, and the possibility of miniaturization [13].