Rapid and Sensitive Fluoroimmunoassay Based on Quantum Dots for Detection of Melamine in Milk

Abstract

A rapid and sensitive indirect competitive fluorescence-linked immunosorbent assay (icFLISA) method was developed for detection of melamine in milk based on secondary antibody (Ab₂)-conjugated quantum dots (QDs). The sensitivity of icFLISA with a limit of detection (LOD) of melamine (3.88 ng mL⁻¹) and 50% inhibition value (IC₅₀) (31.58 ng mL⁻¹), was much higher than that of icELISA. As a proof of principle, recovery tests involving four fortification levels (150, 80, 40, and 20 ngmL⁻¹) in blank samples were also performed. The recoveries ranged from 80.85 to 110.54% with coefficient of variations (CVs) of 2.82–8.82%. When challenged with authentic samples, these results of icFLISA were consistent with that of icELISA, immuno-chromatographic assay and gas chromatography-single quadruple mass spectrometry (GC-MS)method, indicating that icFLISA can be considered as a new screening method for detection of melamine in milk.

Keywords:

• Fluoroimmunoassay
• icFLISA
• Melamine
• Quantum dots (QDS)

Acknowledgments

J. Wu and F. Xu contributed equally to this work. We gratefully acknowledge grants from the National Natural Science Funds of China (31072171), the Special Fund for Agro-scientific Research in the Public Interest (No. 2012030692), and the Modern Agriculture Industry System Innovation in Beijing City Team, and Program for Changjiang Scholars and Innovative Research Team in University of China (No. IRT0866).

Notes

Note: When IC₅₀ was the lowest, the concentration of Ag and Ab₁ was selected for the next step.

^a Ratios of coating antigens (dilution-fold) to primary antibody (dilution-fold).

Note:Every point was replicated five times.