Simple and sensitive lead ion detection based on difference of gold monomer ratio using dark field microscope as readout system

Abstract

Small amount of lead ions (Pb2+) can cause great harm to human health, it is important to develop some simple but sensitive methods to detect Pb2+ quickly and accurately. In this study, a sensitive method has been developed for Pb2+ detection based on the difference of gold monomer ratio using a dark field microscope (DFM) as readout system. The proposed method employed single-particle gold nanoparticles (AuNPs) and 8–17 DNAzyme as signal converter and identification unit, respectively. The 8–17 DNAzyme consists of a catalytic strand and a substrate strand, the 5′ end of the two strands are modified with sulfhydryl groups. The 8–17 DNAzyme is firmly modified on the surface of AuNPs (50 nm, AuNPs1) in advance, in the absence of Pb2+, AuNP aggregation is occurred by adding AuNPs (20 nm, AuNPs2) as they can interact with the other end of the dsDNA. In the presence of Pb2+, due to the specific cleavage of the substrate chain by Pb2+, another –SH leaves away from AuNPs1, the aggregation of AuNPs cannot be occurred. AuNP aggregates can be easily distinguished from the monomers under DFM because the aggregation can induce green-to-yellow scattering color changing, and the monomer ratio summarized by Image J can be used for quantitative analysis. The linear response range is 0.1–100.0 pM with a detection limit of 0.075 pM. The proposed method has been applied to detect Pb2+ in lake water and human blood serum samples with satisfied results.