Dual-mode SERS and colorimetry combined with smartphone-assisted visual detection of Cr(VI) utilizing Au@Ag...

To address the urgent requirements for fast and on-site hexavalent chromium (Cr(VI)) detection, we developed a dual-mode sensing platform integrating surface-enhanced Raman spectroscopy (SERS) and colorimetry combined with smartphone-assisted visual detection using gold-core silver-shell nanoparticles (Au@Ag NPs). The SERS mode leveraged the plasmonic enhancement of Au@Ag NPs, achieving ultrahigh sensitivity with a detection limit of 0.074 nM and a linear range spanning five orders of magnitude. Simultaneously, the colorimetric mode utilized smartphone-assisted RGB (Red-Green-Blue) analysis to quantify Cr(VI)-induced nanoparticle etching, attaining a detection limit of 2.5 µM, surpassing conventional colorimetric sensors. The synergy of dual-mode detection enabled cross-validated quantification: SERS for trace-level determinations and smartphone-based colorimetry for rapid on-site screening. This platform demonstrated exceptional selectivity against interfering ions and robust performance in real-world applications, including rice and environmental water samples, with recoveries of 98.10-104.36%. By combining nanotechnology with portable devices, our work provides a cost-effective, user-friendly, and field-deployable solution for Cr(VI) monitoring in environmental safety and food quality control.