Label-free electrochemical aptasensor based on gold nanoparticles/titanium carbide MXene for lead detection with its reduction peak as index signal

Lead (Pb2+) is a common heavy metallic pollutant in the environment with severe side-effects, and it can lead to chronic poisoning towards humans. Hence, the monitoring of Pb2+ in environments is highly important as a dangerous water pollutant by a simple method. In this research, a label-free electrochemical aptamer sensor (aptasensor) based on the gold nanoparticles/titanium carbide (AuNPs/Ti3C2-MXene) with an interesting strategy: the reduction peak of Pb2+ as the index signal was prepared for Pb2+ detection. According to characterization results, Ti3C2-MXene nanosheets display an excellent supporting base with uniform distribution of the AuNPs without any aggregation, which is beneficial for the immobilization of Pb2+ aptamer. Besides, the sensing interface of the developed aptasensor was constructed by the stepwise assembly of Ti3C2-MXene, AuNPs, and thiol-modified aptamer of Pb2+. On interaction with Pb2+, the Pb2+ aptamer on the electrode surface generates a conformational change from a single-stranded oligonucleotide, resulting in a G-quadruplex stable structure. After that, Pb2+ can be successfully captured, and reduction peak currents can be directly detected by the negative scan of square wave voltammetry (NSSWV). Under optimal experimental conditions, the reduction peak currents of Pb2+ displayed a good linear relationship with the logarithm of Pb2+ concentrations from 5 x 10(-7) to 3 x 10(-4) M, and its detection limit was estimated to be 3 x 10(-7) M. In addition, the prepared aptasensor exhibited excellent repeatability, good stability, high selectivity, and high reproducibility, indicating its great potential for Pb2+ environmental monitoring with recovery range 96.97-108.03%.