Label-free and enzyme-free strategy for sensitive electrochemical lead aptasensor by using metal-organic frameworks loaded with AgPt nanoparticles as signal probes and electrocatalytic enhancers

Herein, based on G-rich lead-specific aptamer (LSA) as the recognition element of target lead ion (Pb2+), a label-free and enzyme-free electrochemical aptasensor for Pb2+ was developed by using metal-organic frameworks (MIL-101(Fe)) decorated with AgPt nanoparticles (AgPtNPs) as electrochemical probes and signal enhancers. The as-prepared AgPtNPs/MIL-101(Fe) that presented both inherent redox activity from MIL-101(Fe) and excellent electrocatalytic activity was further conjugated with single-strand DNA partially complementary to LSA (CS). In the presence of Pb2+, the G-rich LSA, being incubated onto the modified electrode surface, was specifically folded to be stable G-quadruplex structure. Through the DNA hybridization reaction between LSA and CS, the unfolded G-rich LSA captured the proposed signal probes CS-immobilized AgPtNPs/MIL-101(Fe) in the electrode surface. As a result, the detectable electrochemical signal generated by MIL-101(Fe) was dependent on Pb2+ concentration. The cooperative electrocatalysis of AgPtNPs and MIL-101(Fe) effectively enhanced the response signal and greatly improved the detection sensitivity. Thus, the developed aptasensor for Pb2+ displayed a wide linear range from 0.1 pM to 100 nM with a detection limit of 0.032 pM, as well as excellent specificity, good stability, and acceptable reproducibility. This would make the proposed label-free and enzyme-free method be promising and potential candidate for sensitive and cost-effective detection of Pb2+ in real samples.