Abstract
Protein aggregation of alpha-synuclein (α-Syn) is implicated in Parkinson’s disease (PD), and, thus, α-Syn aggregates are a potentially promising candidate biomarker for PD diagnosis. Here, we describe a simple and sensitive electrochemical sensor to monitor the aggregation of α-Syn for early PD diagnosis. The sensor utilizes methylene blue (MB)-tagged aptamer (Apt) adsorbed on electrochemically reduced graphene oxide (ERGO) by π–π stacking. The binding of α-Syn oligomer to the Apt induces desorption of the Apt from the ERGO surface, which leads to the electrochemical signal change. The resulting sensor allowed the highly sensitive and selective detection of α-Syn oligomer according to the voltammetric change. Under optimized conditions, the linear range of detection was observed to be from 1 fM to 1 nM of the α-Syn oligomer and the limit of detection (LOD) was estimated to be 0.64 fM based on S/N = 3. The sensor also showed good reproducibility and stability, enabling real sample analysis of the α-Syn oligomer in human blood serum. With its ultrasensitivity and good performance for α-Syn oligomer detection, the sensor provides one promising tool for the early diagnosis of PD.
Highlights
Parkinson’s disease (PD) is the second most common neurodegenerative disorder that causes a person to lose control over some body functions [1,2]
The modification of electrochemically reduced graphene oxide (ERGO)-glassy carbon electrode (GCE) with Apt resulted in an ip decrease and ∆Ep increase, due to the repulsive forces between the [Fe(CN)6 ]3− and the negatively charged phosphate ions formed on the electrode surface by the Apt coating
The modification of the electrode with Apt caused a large increase in Rct value, implying that the negatively charged Apt was immobilized on the ERGO-GCE and the phosphates in Apt repelled the negatively charged [Fe(CN)6 ]3− ions
Summary
Parkinson’s disease (PD) is the second most common neurodegenerative disorder that causes a person to lose control over some body functions [1,2]. There has been an increase in demand for early PD diagnosis to enable early neuroprotective treatment leading to better clinical results and eventually better quality of life in PD patients [10,11,12]. Current findings have shown that the pathogenesis of PD may be contributed by the development of Lewy bodies, abnormal protein aggregations at the synaptic terminal of midbrain dopaminergic neurons. Α-synuclein (α-Syn) is known to be the main underlying protein responsible for Lewy bodies [13,14]. The degradation system of α-Syn is presumed to be defective in pathological conditions, making monomers of α-Syn aggregate into oligomers, which are regarded as the harmful species associated with neuronal death in the early stages of PD [15]. The degradation system of α-Syn is presumed to be defective in pathological conditions, making monomers of α-Syn aggregate into oligomers, which are regarded as the harmful species associated with neuronal death in the early stages of PD [15]. α-Syn oligomer levels are typically 0.01 (0.7 fM)–0.03
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