Colorimetric sensing of Cu(II) ions in water on the basis of selective chemical etching of EDA-capped Ag nanoplates

Cu(II) ions are one of the essential mineral elements in the human body, but can pose a substantial health risk to people exposed to high concentrations of Cu(II) ions over a long period. Therefore, the ability to detect Cu(II) ions in drinking water is important. In this study, a novel colorimetric sensing probe for the easy and onsite detection of Cu(II) ions in drinking water was developed. The probe was constructed through selective chemical etching of triangular Ag nanoplates with tunable localized surface plasmon resonance (LSPR) properties. Ethylenediamine (EDA) was used as an organic capping agent to improve the chemical stability of triangular Ag nanoplates. Selective chemical etching of the EDA-capped Ag nanoplates in the presence of Cu(II) ions as a result of the formation of a coordination complex between the EDA and Cu(II) ions caused remarkable changes in the nanoplates' LSPR characteristics. On the basis of this phenomenon, a novel colorimetric sensing probe capable of detecting Cu(II) ions in drinking water at concentrations above the safety limit was developed. Our findings were also extended to develop a portable and paper-based sensing probe with good long-term stability to overcome the shortcomings of liquid-phase colorimetric sensors without requiring a spectrometer. The proposed colorimetric sensing probes provide accurate results even with a real sample and offer numerous advantages over conventional sensing platforms, including clearly distinguishable color changes that can be observed by the naked eye; thus, the proposed probes can be used for the selective, reliable, and low-cost point-of-care detection of Cu(II) ions in water.