Colorimetric detection of melamine during the formation of gold nanoparticles

Abstract

A sensitive and simple colorimetric method for determination of melamine was reported based on the seedless production of gold nanoparticles (Au-NPs). Au-NPs were synthesized by using pyrocatechol-3,5-disodiumsulfonate (PD) as reducer without adding nanoparticles seeds and stabilizing agent. PD can form intramolecular hydrogen-bonding in solution by adjacent sulfurnate and α-phenolic hydroxyl group, resulting in its weak reducing capacity and thus the synthesis of Au-NPs was slow. While in the presence of melamine, PD reacted with melamine through hydrogen-bonding. Therefore, the intramolecular hydrogen-bonding of PD was interrupted by melamine, and the α-phenolic hydroxyl group was free to reduce Au 3+, hence, the synthesis of Au-NPs was accelerated. Especially, the presence of melamine led to a shift in the surface plasmon bond and a color change of Au-NPs from green to yellow. Results showed that the absorbance ratio ( A 436/ A 600) was linear with the logarithm of melamine concentration in the range of 4.8 × 10 −9 to 1.6 × 10 −6 M with a correlation coefficient of 0.9949. The detection limit (3 σ) obtained by UV–vis spectrum was 6.4 × 10 −10 M (i.e., 0.08 ppb). The proposed method was applied successfully to the determination of melamine in pretreated liquid milk products, and the recoveries were from 93% to 107%.