A novel one-step triggered signal-on/off electrochemical sensing platform for lead based on the dual-signal ratiometric output and electrode-bound DNAzyme assembly

A simple and novel one-step triggered ratiometric electrochemical biosensor was designed for lead (Pb2+) based on the highly specific lead-dependent DNAzyme and dual-signal output mode. The biosensor consists of a thiolated methylene blue-labeled DNA (MB-P1) as catalytic probe and signal-on readout, and a complementary strand modified with ferrocene (Fc-P2) as substrate probe and signal-off output. The presence of Pb2+ could activate the DNAzyme and cleave the sessile phosphodiester of the Fc-P2 into two fragments, which lead to the departure of Fc from the sensing interface along with the single stranded MB-P1 near the electrode surface. Therefore, the Pb2+ recognition event resulted in both the signal-on of MB and the signal-off of Fc for dual-signal ratiometric electrochemical readout. Combined with the efficient recognition capacity of the designed DNAzyme and the dual-signal amplification strategy, the proposed biosensor showed a wide detection range from 0.1 nM to 5 mu M with a detection limit of 45.8 pM (S/N = 3). Meanwhile, this DNAzyme-based Pb2+ biosensor exhibits reasonable selectivity, fast analytical speed, acceptable fabrication reproducibility, and operational convenience. More importantly, the system is capable of detecting Pb2+ in biological fluid such as serum, suggesting promising applications of this biosensor in on-site and real-time clinical Pb2+ detection. (c) 2017 Published by Elsevier B.V.