A highly sensitive DNAzyme-based SERS biosensor for quantitative detection of lead ions in human serum

Lead ions (Pb²⁺), one form of the toxic heavy metal, have drawn significant attention due to their harmful effects on human health and the environment. Although many analytical techniques have been developed over the past few decades, the development of a sensitive, selective, and rapid method to detect Pb²⁺ remains a challenge. In this work, we developed a sensitive surface-enhanced Raman scattering (SERS) biosensor for highly sensitive detection of Pb²⁺ by using DNAzyme-modified Fe₃O₄@Au@Ag nanoparticles (Fe₃O₄@Au@Ag NPs). Firstly, the thiolated 5'-Cy3 DNA probe was modified on the surface of Fe₃O₄@Au@Ag NPs, which hybridized with the Pb²⁺-specific DNAzyme to form a SERS biosensor, and the Cy3 labels were used to detect Pb²⁺. In the presence of Pb²⁺, the DNAzyme cleaves the Cy3-labeled DNA probe, leading to the release of Cy3-labeled DNA probe from the Fe₃O₄@Au@Ag NPs. Therefore, the Raman intensity of the Cy3 labels decreases. The proposed biosensor exhibited excellent linearity in the range from 0.01 to 1.0 nM, with a limit of detection for Pb²⁺ of 5 pM. It features superior selectivity to Pb²⁺ over other interfering metal ions and good application in the determination of Pb²⁺ in tap water and human serum samples. The SERS biosensor provides a novel' simple and sensitive method for detection of Pb²⁺ and sheds new light on the design and synthesis of analogous SERS biosensors for the detection of other heavy metal ions.