Aptasensors for the selective detection of alpha-synuclein oligomer by colorimetry, surface plasmon resonance and electrochemical impedance spectroscopy

Soluble alpha-synuclein (α-syn) oligomer is believed to be a reliable molecular biomarker for diagnosis of Parkinson's disease (PD). Thus, it is critical to develop a simple method for the selective detection of α-syn oligomer with low cost as well as high sensitivity. In this paper, we reported the label-free detection of α-syn oligomer using a DNA aptamer as the bioreceptor with the techniques of gold nanoparticles (AuNPs)-based colorimetric assay, surface plasmon resonance (SPR) and electrochemical impedance spectroscopy (EIS). In the colorimetric assay, the aptamer adsorbed onto the surface of AuNPs to prevent the salt-induced aggregation of the nanoparticles. However, the specific binding of α-syn oligomer to aptamer prevented the absorption of aptamer onto the surface of AuNPs. As a result, the aggregation of AuNPs was triggered by high concentration of salt with a color change from red to blue. In the SPR- or EIS-based surface analysis, specific binding of α-syn oligomer to the aptamer immobilized onto the gold film or electrode surface led to an increase in the SPR dip shift or the electron-transfer resistance. The detection limits of the colorimetry, SPR and EIS were found to be 10 nM, 8 pM and 1 pM, respectively. The amenability of this method to α-syn oligomer analysis in a biological matrix was demonstrated by assay of α-syn oligomer in serum.