Simultaneous detection of trace toxic metal ions, Pb2+ and Ag+, in water and food using a novel single-labeled fluorescent oligonucleotide probe

Owing to the high toxicity of lead (II) (Pb2+) and silver (I) ions (Ag+) to aquicolous organisms, it is highly desirable to develop a sensitive method for the simultaneous detection of Pb2+ and Ag+. In this work, a novel and sensitive single-labeled fluorescent oligonucleotide (OND) probe is designed to simultaneously detect based on the specific complexation of Ag+ to cytosines, the special induction capacity of Pb2+ to guanine-rich OND to form G-quadruplex and the inherent quenching ability of G-quadruplex to the hexachloro fluorescein (HEX). The Ag+-induced hairpin-link structure makes HEX labeled at the 5′-termini close to the Pb2+-induced G-quadruplex connected at the 3′-terminin, resulting in a remarkable fluorescence quenching owing to photoinduced electron transfer (PET) process from G-quadruplex to HEX. At 298 K, the apparent associating constant between them is 1.85 × 108 (L/mol). Using this system, we can simultaneously detect the Pb2+ and Ag+ over the linear response range of 1-100 nmol/L with a detection limits of 96 pmol/L and 21 pmol/L, respectively. Through the assay in real samples, it is known that this system could be applied to accurately monitor the trace Pb2+ and Ag+ in aqueous solution.