Investigation On The Determination Of Melamine By Surface Plasmon Resonance

Abstract:Surface plasmon resonance (SPR) is a sensitive optical technique, being capable of determining the refractive index or mass change on the sensor chip. The attractive features of SPR include high sensitivity, label-free and real-time measurements, and now SPR has been widely used for monitoring antibody-antigen, DNA-DNA, DNA-protein, protein-protein and receptor-ligand interactions.Melamine (C3H6N6) is an illegal additive to milk. As a nitrogen-rich compound (66%nitrogen content), the addition of melamine to food and milk can significantly enhance the nitrogen contents and the continuous intake of melamine-contaminated infant milk and other milk products can lead to severe health problems and illnesses. As a result, rapid and sensitive detection of melamine is of great importance for food safety. Since small molecules are difficult to be directly determined by SPR, two kinds of methods have been proposed via signal amplification schemes. The developed methods are convenient and cost-effective, holding great promise for detection of melamine in milk.1. SPR assays of melamine were carried out based on a competitive reaction in which the assayed melamine with varying concentrations in solution competed with the pre-immobilized NH2-melamine or BSA-melamine conjugate for the anti-melamine monoclonal antibody (mAb) in solution. The NH2-melamine or BSA-melamine conjugate was first immobilized on the carboxymethylated dextran-covered SPR chips, followed by the injection of the mixed solution of melamine and anti-melamine mAb with a fixed concentration. By examining the SPR signals caused by the attached monoclonal antibodies, the concentration of melamine in solution could be determined. The chips could be regenerated via injection of NaOH, thus, high-throughput assays could be attained. In comparison with NH2-melamine, the BSA-melamine conjugate has proven to be effective for elimination of nonspecific adsorption.2. Relying on the specific interaction between melamine and thymine (T), an SPR method for the detection of melamine has been developed. The DNA probe (NH2-A15) was first immobilized on the carboxymethylated dextran-covered SPR chips, and this was followed by the injection of the mixed solution of melamine, target DNA (T15-biotin) and streptavidin with a fixed concentration. The specific interaction between T15-biotin and melamine led to fewer T15-biotin molecules to be attached to the sensor chip, and the SPR signal caused by the incorporation of streptavidin was decreased. The increase in the melamine concentration led to the decrease in the SPR response. The linear ranges for melamine detection were0.317-31.7nM and31.7-634nM.