Portable Au Nanoparticle-Based Colorimetric Sensor Strip for Rapid On-Site Detection of Cd²⁺ Ions in Potable Water

Simple, rapid, and instrument-free detection of cadmium ions (Cd²⁺) with a portable device is essential to prevent the contamination of potable water. Herein, we propose a simple, fast, and low-cost method for the real-time/on-site detection of Cd²⁺ using glutathione-modified Au nanoparticles (GSH-AuNPs) deposited on a polyethylene terephthalate (PET) sensor strip. To fabricate the sensor strip, a paint composed of GSH-AuNPs and polyvinylpyrrolidone was prepared. Subsequently, the GSH-AuNP paint was deposited on a mold fixed on the PET substrate and dried in ambient air. The GSH-AuNPs deposited on the PET substrate quickly redispersed in water, turning the water red. However, the GSH-AuNPs aggregated in water samples containing Cd²⁺, turning the water blue. The limit of detection of this Cd²⁺ sensor strip is 18.8 nM, which is comparable to the maximum contamination level of 44.5 nM Cd²⁺ in potable water stipulated by the US Environmental Protection Agency. Finally, we demonstrate that the GSH-AuNP-based sensor strip can be used in the on-site detection of Cd²⁺ in real samples such as tap water.