Highly sensitive and rapid detection of melamine in milk products by planar waveguide fluorescence immunosensor (PWFI)

An indirect competitive immunoassay has been developed using the planar waveguide fluorescence immunosensor (PWFI) based on the principle of immunoreaction and total internal reflect fluorescent, offering simple, rapid and sensitive detection and quantification of melamine in buffer and milk products. The chip immobilized by BSA-Mel was reusable and highly resistive to non-specific binding of proteins. The regeneration of the sensor allows more than 100 assay cycles within 20 min for each assay cycle. For the standard curve, the limit of detection of 6.6 μg/L and the quantitative detection range of 26.6–517.5 μg/L were obtained when the concentration of antibody labeled by Cy5.5 was 2.4 μg/mL. The results meet the requirements for the maximum amount of melamine allowed in infant formula (1.0 mg/kg) and all the other foods (2.5 mg/kg) set by the WHO, which were better than most other standard methods. Few cross-reactivity effects were noted to occur among closely resembling pollutant molecules during the melamine determination process. Recoveries from the melamine-fortified blank samples were between 89.8 and 103.2% with relative standard deviation lower than 8.1%. The results were in good correlation (R2 = 0.9963) to those measured by LC–MS/MS.