A novel curcumin assay with the metal ion Cu (II) as a simple probe by resonance light scattering technique

A fantastic resonance light scattering (RLS) enhancement phenomenon was found when the interaction between the metal ion Cu (II) and a natural antioxidant curcumin (C21H20O6) occurred in certain conditions. Based on this phenomenon, a novel and convenient assay of curcumin was developed and successfully applied on the determination of curcumin in human urine samples. This assay applied the RLS technique with a common metal ion Cu (II) as the spectral probe. In the pH range of 6.5–7.5, the interaction between Cu (II) and curcumin occurred and the weak RLS intensity of Cu (II) was greatly enhanced by curcumin. The maximum peak was located at 538.5 nm. Under the optimum conditions, the enhanced RLS intensity was proportional to the concentration of curcumin ranging from 0.4 to 60 μg ml−1 with the detection limit of 0.07 μg ml−1. The synthetic and human urine samples were determined satisfactorily. Good recoveries (98.8–102.5%) were obtained in the determination of urine samples, which proved that the assay proposed was reliable and applicable in the determination of curcumin in body fluid. In this work, the RLS and fluorescence spectral characteristics of the chemicals, the optimum conditions of the reaction and the influencing factors were investigated.