Shell-switchable SERS blocking strategy for quantitative copper ion detection using single-particle SERS probes

Accurate detection of copper ions (Cu²⁺) is crucial for environmental protection and human health. In this work, we develop a shell-switchable surface-enhanced Raman scattering (SERS) blocking strategy for Cu²⁺ quantification using single-particle SERS probes. In the assay, single bilayered Raman-intense gold nanostructures with hidden tags are used as single-particle SERS probes. The Au shell functions as a switch and it is modulated through Cu²⁺-induced oxidative etching, enabling controllable regulation of Raman intensity. Based on this principle, Cu²⁺ quantification is achieved by correlating the SERS intensity change (ΔI) with concentration, yielding a wide range of 10⁻⁷-10⁻³ M and a limit of detection (LOD) of 33.8 nM. The developed sensing strategy exhibits outstanding sensitivity and high selectivity for Cu²⁺ against various interfering metal ions. Furthermore, it has been successfully applied to Cu²⁺ detection in real water samples, demonstrating its reliability and practical applicability. In addition, this system can be further extended to perform chemical logic operations, highlighting its potential for intelligent sensing applications.