Lable-Free LSPR-Based Colorimetric Detection of α-Synuclein, a Biomarker of Parkinson’s Disease, in Saliva

Parkinson’s disease (PD) is one of the neurodegenerative disorders affecting millions of people around the world. Alpha-synuclein (
$\alpha $
-syn) as the key protein in the pathogenesis of PD is considered a promising candidate prognostic marker of PD. Various factors, including the presence of some metal ions, induce aggregation of
$\alpha $
-syn. It has been shown that cupric ions (Cu
$^{{2}+}$
) have more binding sites and greater affinity to the
$\alpha $
-syn than other metal ions. In this study, a colorimetric sensor was fabricated for
$\alpha $
-syn detection based on the specific interaction between
$\alpha $
-syn and Cu
$^{{2}+}$
leading to aggregation of gold nanoparticles (AuNPs). The sensor showed a distinct response to
$\alpha $
-syn, with the detection limit of 10 nM, and could discriminate between monomers, oligomers, and fibrils of
$\alpha $
-syn. This finding is of great interest due to different neurotoxicity of monomers and aggregated forms of
$\alpha $
-syn. The discrimination of different concentrations of
$\alpha $
-syn in saliva was shown by colorimetry and linear discriminant analysis (LDA).