A flow-batch manipulated Ag NPs based SPR sensor for colorimetric detection of copper ions (Cu²⁺) in water samples

Using flow-batch analysis, a highly sensitive and selective method for automatic colorimetric detection of copper ions (Cu²⁺) was produced on the basis of the surface plasma resonance (SPR) of silver nanoparticles (Ag NPs). The Ag NPs were catalytically etched by thiosulfate in the presence of Cu(NH₃)₄²⁺, resulting in a color change of the solution induced by the absorbance decrease at 401nm of the SPR peak of Ag NPs. The proposed method showed high selectivity for Cu²⁺ over various metallic ions, including Fe³⁺, Mn²⁺, Co²⁺, Ni²⁺, Zn²⁺, Pb²⁺, Ba²⁺, Cd²⁺, Bi³⁺, Sb²⁺, As³⁺, Hg²⁺, Cr³⁺ and K⁺. The linear range was 0.5-35μg/L with a coefficient of 0.9954. The limit of detection was as low as 0.24μg/L. The relative standard deviation (RSD, n=7) for the determination of Cu²⁺ spiked samples at concentrations of 10μg/L was 1.21% and for 25μg/L was 1.03%. The proposed method was successfully applied to analyze Cu²⁺ in lake water, tap water, rainwater and bottled water samples, as well as leaf samples for food packaging. The results were in good agreement with those obtained by graphite furnace atomic absorption spectrometry, the classical technique.