α-synuclein oligomer is a marker of Parkinson's disease. The traditional enzyme-linked immunosorbent assay for α-synuclein oligomer detection is not conducive to large-scale application due to its time-consuming, high cost and poor stability. Recently, DNA-based biosensors have been increasingly used in the detection of disease markers due to their high sensitivity, simplicity and low cost. In this study, based on the DNAzyme-driven DNA bipedal walking method, we developed a signal-on electrochemical sensor for the detection of α-syn oligomers. Bipedal DNA walkers have a larger walking area and faster walking kinetics, providing higher amplification efficiency compared to conventional DNA walkers. The DNA walker is driven via an Mg 2+ -dependent DNAzyme, and the binding-induced DNA walker will continuously clamp the MB, resulting in the proliferation of Fc confined near the GE surface. The linear range and limit of detection were 1 fg/mL to 10 pg/mL and 0.57 fg/mL, respectively. The proposed signal-on electrochemical sensing strategy is more selective. It will play a significant role in the sensitive and precise electrochemical analysis of other proteins.
T4 polynucleotide kinase (T4 PNK), a bifunctional repair enzyme, catalyzes the transfer of γ-phosphate residues from adenosine triphosphate (ATP) to 5′- hydroxyl termini in nucleic acids，which plays an essential role in regulating DNA phosphorylation modes during the repair of damaged DNA. Herein, a sensitive DNAzyme-driven DNA walker biosensor was developed for amplified electrochemical detection of T4 PNK activity and inhibition based on T4 PNK-triggered phosphorylation reaction and λ exonuclease (λ exo) cleavage. A novel functional hairpin-shaped swing arm DNA (SA) containing a DNA sequence of the Pb 2+ -dependent DNAzyme is designed to specifically bind to and hydrolyze the substrate strand (rSS) sequence that can drive DNA walker. Upon the reaction of SA， T4 PNK and ATP, λ exo removes the mononucleotides from the stem of the phosphorylated SA, unfolding the hairpin structure and initiating DNAzyme-driven DNA walker. Subsequently, the DNA walker can repeatedly bind and cleave rSS with the aid of Pb 2+ , releasing the methylene blue (MB) - labeled fragment of rSS. The T4 PNK activity can be facilely monitored by recording the electrochemical signal change of MB. The proposed biosensor exhibited a broad linear range from 0.01 U mL −1 to 15 U mL −1 with a low detection limit of 0.001 U mL −1 . The proposed biosensor has also been utilized to screen the T4 PNK inhibitors and exhibited good performance in real sample analysis, making such a strategy hold potential promise in biological fields and clinical diagnosis.
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