A simple, reliable and sensitive colorimetric visualization of melamine in milk by unmodified gold nanoparticles

• Published in: Analyst (London) 2010-01, Vol.135 (5), p.17-175
• Main Authors: Chi, Hong, Liu, Bianhua, Guan, Guijian, Zhang, Zhongping, Han, Ming-Yong
• Format: Article
• Language: English
• Subjects: Agglomeration; Analytical chemistry; Animals; Cattle; Chemistry; Citric Acid - chemistry; Colorimetry - methods; Crosslinking; Exact sciences and technology; Gold; Gold - chemistry; Melamine; Metal Nanoparticles - chemistry; Milk; Milk - chemistry; Nanoparticles; Nanostructure; Spectrometric and optical methods; Spectrophotometry, Ultraviolet; Sulfates - chemistry; Triazines - analysis; Visualization
• ISSN: 0003-2654; 1364-5528
• DOI: 10.1039/c000285b

In this paper, we report a simple, reliable and sensitive colourimetric visualization of melamine in milk products using citrate-stabilized gold nanoparticles (Au NPs). Upon exposure to ppb-level melamine, gold nanoparticle solution exhibits a highly sensitive colour change from red to blue and rapid aggregation kinetics within the initial 5 min, which can directly be seen with the naked eye and monitored by UV-vis absorbance spectra. As confirmed by the comparison with six other typical amino compounds, the melamine molecule itself contains multiple strong-binding sites to the surface of Au NPs and thus plays a role of molecular linker to efficiently crosslink Au NPs. Further evidence is that the sensitivity is significantly improved when NaHSO 4 is added to promote the ligand exchange between citrate and melamine at the surface of Au NPs. The NaHSO 4 -optimized Au NPs system provides a rapid colourimetric assay for the rapid detection of melamine down to ∼25 ppb in real milk products. Melamine can directly induce the aggregation of unmodified Au nanoparticles without the aid of a specific acceptor through its multiple strong-binding sites to the surface of Au nanoparticles.