Silver Nanoplates:  A Highly Sensitive Material toward Inorganic Anions

This paper demonstrates a simple sensing method to detect inorganic anions by silver nanoplates (edge length of ∼70 nm and thickness of ∼2 nm) in aqueous solution. By this method, the solution system containing silver nanoplates shows a high sensitivity on the order of 1 × 10-6 M in detecting halides, phosphate, and thiocyanate ions in water at room temperature. The sensitivity could be identified by the shift in the surface plasmon resonance (SPR) band in UV−vis spectrum. The selectivity of such a sensing system toward various anions was also studied, and it was found that this sensing system could distinguish individual anions (e.g., Cl-, Br-, I-, H2PO4 -, and SCN-) from other anions (e.g., F-, SO4 2-, CH3COO-, NO3 -, and ClO4 -) and inorganic cations (e.g., Zn2+, Cd2+, and Cu2+) under the given conditions. The sensing mechanism was also analyzed. It was proposed that the particle surface electron charging, which is mainly determined by the interaction tendency between silver atoms and various inorganic anions in water, is responsible for the shift in the SPR observed. The need for further studies was finally discussed, particularly for systems composed of mixed anions.