"Signal-on" SERS sensing platform for highly sensitive and selective Pb²⁺ detection based on catalytic hairpin...

In this work, a surface-enhanced Raman scattering (SERS) sensing strategy was proposed for the analysis of lead ion (Pb²⁺) with high sensitivity and specificity based on the high specificity of the catalytic nucleic acids (DNAzymes) to Pb²⁺ and the catalytic hairpin assembly (CHA) amplification. First, the Pb²⁺-DNAzyme initiated the reaction by target Pb²⁺ and released a linear DNA (rS1). Second, the hairpin DNA 1 (H1) was immobilized on the SERS substrate surface via Ag-S bond. Then, the rS1 could cyclically trigger the allosteric effects of CHA amplification and the H1 was opened and then the R6G-labeled hairpin probe 2 (H2) hybridized with H1 to form H1-H2 double-stranded and the released rS1 could initiate the next cycle of CHA reaction. This process made the Raman tag of R6G close to the surface of SERS substrate, and the intensity of SERS signal from R6G labels increase with the increase of concentration of target Pb²⁺. Benefiting from outstanding performances of the Pb²⁺-specific DNAzymes and enzyme-free CHA amplification system, this biosensor exhibits good sensitivity for Pb²⁺ with a limit of detection of 0.42 pM. More importantly, this developed detection platform could be employed for reliable analysis of Pb²⁺ in real environment system.