Dual-mode colorimetric sensing detection of Cr(III) enabled by target-induced aggregation of α-Sulfophenylacetic acid-functionalized silver nanoparticles

The rapid, on-site quantification of trivalent chromium (Cr(III)) is crucial for environmental risk assessment, yet conventional analytical methods are severely hampered by their reliance on bulky instrumentation. To address this challenge, we report a portable, dual-mode colorimetric sensing platform centered on the specific interaction between Cr(III) and α-sulfophenylacetic acid-functionalized silver nanoparticles (D-SFA-AgNPs). This interaction triggers the controlled aggregation of nanoparticles, resulting in a distinct yellow-to-gray color change and a significant red-shift in the localized surface plasmon resonance (LSPR) spectrum. To fully leverage this optical response, a low-cost, Arduino-based smart analyzer was engineered, integrating a Red-Green-Blue (RGB) colorimetric mode for rapid screening and a multi-channel spectral mode for trace analysis. Under optimized conditions, the platform achieved a rapid response (< 1 min) with a linear dynamic range of 0.033–100 μg L −1 . The limit of detection (LOD) was determined to be 4.60 μg L −1 , which is significantly lower than the World Health Organization (WHO) guideline for drinking water (50 μg L −1 ). Furthermore, analytical validation in real water samples demonstrated excellent spike recoveries (97.6%–107.6%) and high precision (RSD < 5.9%), showing high consistency with the gold-standard inductively coupled plasma-mass spectrometry (ICP-MS) method. Consequently, by synergizing the Arduino-based open-source hardware with dual-mode sensing, this work provides a cost-effective solution for the point-of-need monitoring of Cr(III), holding great potential for environmental surveillance even in resource-limited areas.