title: A simple, reliable and sensitive colorimetric visualization of melamine in milk by unmodified gold nanoparticles.
abstract: 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 approximately 25 ppb in real milk products.
authors.affiliation: Institute of Intelligent Machines, Chinese Academy of Sciences, Hefei, Anhui 230031, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Chi
authors.forename: Bianhua
authors.initials: B
authors.lastname: Liu
authors.forename: Guijian
authors.initials: G
authors.lastname: Guan
authors.forename: Zhongping
authors.initials: Z
authors.lastname: Zhang
authors.forename: Ming-Yong
authors.initials: MY
authors.lastname: Han
mesh_terms: D000818:Animals; D002417:Cattle; D019343:Citric Acid / Q000737:chemistry; D003124:Colorimetry / Q000379:methods*; D006046:Gold / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*; D008892:Milk / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013431:Sulfates / Q000737:chemistry; D014227:Triazines / Q000032:analysis*
chemical_list: D013431:Sulfates; D014227:Triazines; C012036:sodium sulfate; D019343:Citric Acid; D006046:Gold; C011907:melamine