Optical detection of melamine in raw milk

Recent cases of food and milk adulteration with melamine have led to a need for rapid and reliable monitoring systems. To meet this requirement, herein, we report a simple and reliable method for the detection of melamine in raw milk using a fiber optic sensing probe. Gold nanoparticles (AuNPs), chemically synthesized by the reduction of HAuCl₄ with citrate were used to develop the sensor. In neutral media, melamine could rapidly induce the aggregation of gold nanoparticles thereby resulting in a red to blue color change. The refractive index of the raw milk changed after interaction with melamine in a concentration dependent manner altered the output light intensity. The developed sensor was found to show linear response in the range of 6.5 to 333 ppm and the limit of detection of melamine is up to 6 ppm in raw milk.