An electrochemical aptasensor for amyloid-β oligomer based on double-stranded DNA as conductive spring

In order to overcome the antibody-based sensor's shortcomings, an electrochemical aptamer (Apt)-based sensor was developed for amyloid-beta(40) oligomer (A beta(40-O)). The aptasensor was constructed by locating Apt and ferrocence (Fc) on streptavidin-modified gold (SA-gold) nanoparticles. The obtained AptFc@SA-gold nanoparticles were linked onto the Au electrode via the connection of double-stranded DNA (dsDNA) as a conductive spring. The determination of A beta(40-O) was performed with square-wave voltammetry (SWV). Upon bio-recognition between Apt and A beta(40-O), the conformation of Apt changed and the formed Apt/A beta(40-O) complex separated from the SA-gold surface. As a result, the surface charge of SA-gold positively shifted, weakening the electrostatic attraction between the SA-gold and the positively charged Au electrode surface (at potential range of 0.1 similar to 0.5 V, corresponding to the Fc redox transformation), and stretching the dsDNA chain. Based on the exponential decay of dsDNA's electron transfer efficiency on its chain stretching, the oxidation current density from Fc decreased and displayed linear correlation to the concentration of A beta(40-O). A wide linear range of 0.100 nM to 1.00 mu M with a low detection limit of 93.0 pM was obtained. The aptasensor displayed excellent selectivity toward A beta(40-O) in contrast to other possible interfering analogs (A beta(40) monomer, A beta(42) monomer, and oligomer) at x100 higher concentrations. The recoveries for A beta(40-O)-spiked artificial cerebrospinal fluid and healthy human serum were 94.0 similar to 104% and 92.8 similar to 95.4%, respectively. The electrochemical aptasensor meets the demands of clinic determination of A beta(40-O), which is significant for the early diagnosis of AD.