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A novel electrochemical aptasensor based on nontarget-induced high accumulation of methylene blue on the surface of electrode for sensing of α-synuclein oligomer

Taghdisi, Seyed Mohammad, Danesh, Noor Mohammad, Nameghi, Morteza Alinezhad, Ramezani, Mohammad, Alibolandi, Mona, Hassanzadeh-Khayat, Mohammad, Emrani, Ahmad Sarreshtehdar, Abnous, Khalil
Biosensors & bioelectronics 2019 v.123 pp. 14-18
Alzheimer disease, aptasensors, biomarkers, blood serum, detection limit, electrochemistry, electrodes, methylene blue, oligonucleotides, transferases
This study describes a novel electrochemical aptasensor for detection of α-synuclein (α-syn) oligomer, an important biomarker related to Parkinson's and Alzheimer's diseases. The sensing platform is based on exonuclease I (Exo I), terminal deoxynucleotidyl transferase (TdT) and methylene blue. The aptasensor exploits the improved sensitivity because of applications of TdT and Exo I and also a label-free aptamer (Apt). Furthermore, direct immobilization of complementary strand of aptamer (CS) instead of Apt on the surface of electrode prohibits Apt self-assembled monolayer aggregation and keeps the function of the Apt. In the absence of α-syn oligomer, TdT enhances lengths of Apt and CS and so, increases accumulation of methylene blue as redox agent on the surface of electrode, leading to a strong current signal. While in the presence of α-syn oligomer, Exo I digests CS on the electrode surface, resulting in less accumulation of methylene blue on the electrode surface and a weak current signal. The relative electrochemical signal of the aptasensor increased linearly with the logarithm of α-syn oligomer concentration in the range from 60 pM to 150 nM. The detection limit was 10 pM. Furthermore, the sensor showed high precision and repeatability for detection of α-syn oligomer in serum samples.