Investigation of Food Adulteration in Milk Products using Gold Nanoparticle based Surface Plasmon Resonance Probes

Abstract

The main objective of this thesis is the detection of food adulteration using gold nanoparticle based surface plasmon resonance probes. This is a surface sensitive technique mainly used to detect analyte or target molecules using nanosubstrates. Here this technique is used to detect food adulteration and contamination in milk products using gold nanoparticles. “Melamine” is a chemical compound generally present in milk based food products mainly in liquid milk, infant formula powder and pet food. Although melamine is not allowed to use as an additive in milk based products however it is illegally added in pet food and infant formula powder to increase apparent crude protein content based on total nitrogen as it contains 66% nitrogen by mass. The excessive intake of melamine can result in the formation of insoluble melamine cyanurate crystal in kidney and can cause renal failure which may lead to uncertain death of pets and infants. In this dissertation a method is developed to analyze milk adulteration in infant formula powder by visual inspection. The method works on the principle that in the presence of melamine GNPs gets aggregated and show a visual color change from ruby red (due to spherical GNPs) to blue (due to aggregation of GNPs). In the presence of melamine, plasmon peak of GNPs shifts from 524 nm to 650 nm. The reason for the aggregation of GNPs are due to the amino group and ring nitrogen of melamine which strongly bind to the surface of citrate stabilized GNPs by the ligand-exchange and this ligand-exchange decreases the electrostatic repulsion between individual GNPs and finally results in the aggregation of GNPs. GNPs based surface plasmon resonance probes can be used to detect less concentration of melamine (2.41 mM) in infant formula powder. This detection limit of melamine is high as compared to Food and Drug Administration (0.01 mM) in infant formula powder but the method can be still used due to its simplicity, rapidity, low cost and reliability in both qualitative and quantitative capabilities.