Colorimetric detection of methionine based on anti-aggregation of gold nanoparticles in the presence of melamine

Abstract A rapid method for the determination of methionine (Met) based on the anti-aggregation of gold nanoparticles (AuNPs) in serum and urine is presented. Melamine (Mel) can induce the aggregation of AuNPs through the ligand exchange between amine groups on melamine and negatively charged citrate ions and then induce color change of the AuNPs solution from wine red to blue. However, the AuNPs is more prone to combining with Met through both Au S and Au N bonds in the presence of Mel, which hinders the aggregation of AuNPs induced by Mel. A good linear correlation (R 2  = 0.996) between absorbance ratio and the Met concentration is obtained over the range from 0 μM to 1.0 μM. The detection limit was estimated as low as 24.5 nM and the recovery of Met added to serum and urine samples was 95.0-105% and 95.0-104%, respectively. The result represents that the method makes this sensor promising for the applications in the development of detecting Met.