Colorimetric sensing of barium ion in water based on polyelectrolyte-induced chemical etching of silver nanoprisms

Because water contamination by barium ion (Ba2+) is still common, the ability to detect Ba2+ in aqueous media is important. However, the development of an easy-to-use and point-of-care sensing method for detecting Ba2+ in aqueous media has proven challenging. In the present study, a colorimetric sensing platform for detecting Ba2+ in an aqueous medium was developed. The platform stands on the basis of the localized surface plasmon resonance (LSPR) properties of Ag nanoprisms, where a strong polyelectrolyte, poly(styrene-4-sulfonate) (PSS), is used as a powerful chemical etchant for the nanoprisms. Upon the addition of PSS to a solution of the Ag nanoprisms, the sharp tips of the Ag nanoprisms were immediately etched and the nanoprisms spontaneously transformed into spheroidal nanostructures, giving rise to dramatic changes in their LSPR properties. The chemical etching reaction of Ag nanoprisms exposed to PSS was retarded in the presence of Ba2+, which enabled the design of a new chemical sensing platform for the sensitive and selective detection of Ba2+ in aqueous media. The proposed Ba2+ sensing platform using highly anisotropic Ag nanostructures and a polyelectrolyte etchant offers numerous advantages over existing platforms, including naked-eye recognition and safe use and handling; hence, the developed platform can be used at the point of care.