Engineered Au@CuO Nanoparticles for Wide-Range Quantitation of Sulfur Ions by Surface-Enhanced Raman Spectroscopy

Efficient detection of sulfide ions (S^2-), especially in a wide quantitative range, is of significance but faces challenges. This work strategizes and fabricates Au@CuO nanoparticles for quantitative surface-enhanced Raman spectroscopy (SERS) detection of the S^2- ions based on the S^2- concentration-dependent ion-solid interactions. We have achieved fast and quantitative S^2- detection in a wide range from 5 ppb to 64,000 ppm (saturation concentration of the S^2- source). We also demonstrated that the optimal CuO shell thickness for the detection is about 7 nm and that the detection can be further improved by prolonging the soaking duration. Moreover, this detection method has also shown the merits of reusable substrates (especially for low S^2- concentrations) and good anti-interference ability to many common anions (Cl^-, NO₃^-, OH^-, HCOO^-, CO₃^2-, and SO₄^2-). Finally, the high feasibility of this detection in actual water (tap water and pond water) has also been demonstrated. This work provides efficient S^2- detection with great potential in practical use and also inspires the design of quantifiable SERS substrates for detecting more small inorganic molecules and ions.