Rapid on-site determination of melamine in raw milk by an immunochromatographic strip

A rapid and simple method was established based on gold nanoparticle-labelled monoclonal antibody probes for the detection of melamine pollution in raw milk. The conditions for conjugation between the antibody and gold nanoparticles were optimised (pH 8.0, antibody concentration 5 mu g mL-1). It gives a single proportional to melamine concentration with a performance time of only 3 min. A practical calibration curve was established with a reader system with limit of detection calculated as 4.47 and 8.34 mu g L-1 with naked eyes. Three structural analogues, atrazine, desethyl-desisopropyl-atrazine and cyromazine, were used to test the specificity of the immunochromatographic strip, and small colour changes on the strip test line were found even at the 500 ng mL-1 spiked level. Fifty raw milk samples were detected with this strip method, and the resulting data coincided well with results from gas chromatography tandem mass spectrometry. The above-mentioned results showed that this test strip can be used for melamine screening in the daily monitoring of milk.