Colorimetric sensing of copper based on its suppressive effect on cloud point extraction of label free silver nanoparticles

Abstract

Silver nanoparticles exhibit the optical properties of surface plasmon resonance (SPR). This paper describes a method based on both SPR and cloud point extraction of silver nanoparticles (AgNPs) for the determination of copper. Label free AgNPs are enriched into a non-ionic surfactant phase and show strong SPR intensity. Copper(II) suppresses the transfer of AgNPs into the surfactant and decreases the SPR intensity. The decrease in the absorbance of the surfactant rich phase in the presence of Cu(II) is used as an analytical signal for the determination of copper. The influence of chemical variables such as pH of the sample solution, ionic strength, and concentration of the AgNPs on the cloud point extraction was investigated. Under the optimum conditions, the extent of the decrease in SPR absorption intensity was linearly proportional to the concentration of Cu(II) in the range of 0.5–60.0 μg L⁻¹ with a detection limit of 0.1 μg L⁻¹. The relative standard deviation of ten replicate measurements of 40 μg L⁻¹ of Cu(II) was 3.7%. The proposed method was successfully applied in the determination of Cu(II) in food samples with satisfactory results.