A TdT-mediated cascade signal amplification strategy based on dendritic DNA matrix for label-free multifunctional electrochemical biosensing.

We describe a novel label-free amplified multifunctional strategy of dendritic electrochemical DNA sensor based on terminal deoxynucleotidyl transferase (TdT). We have found that the sequence composition of TdT-yielded DNA is largely dependent on the constitution of substrate deoxynucleotides (dNTPs) pool. After rational design of dNTPs pool and controllable TdT polymerization, dendritic protocol has been developed involving two-type amplification strategies; one is the formation of "trunk" and "branch" of the dendritic electrochemical sensor by TdT amplification; the other is the introduction of nucleic acid functionalized Au nanoparticles (DNA-AuNPs) for multiple branching. The results indicate that the G-rich ssDNA, which is synthesized under the condition of 40% deoxyadenosine triphosphate (dATP) and 60% deoxyguanosine triphosphate (dGTP), can be induced to form a long signal strand to G-quadruples (G4) in the presence of Pb(2+). The electrochemical sensing platform is employed for sequence-specific DNA detection and the detection limit is as low as 1 fM. Our multifunctional strategy is further extended to Pb(2+) detection and thrombin aptasensor. This proposed sensor displays excellent sensitivity and selectivity, and is applied for detection in complicated samples successfully.