Visual detection of melamine in milk products by label-free gold nanoparticles

Surface-Enhanced Raman Scattering Liquid Sensor for Quantitative Detection of Trace Melamine in Dairy Products

“…A safety limit for melamine ingestion is officially set at 2.5 ppm for adult food and 1 ppm infant formula by the US Food and Drug Administration (Zhao et al, 2009; http://www.fda.gov/NewsEvents/ Newsroom-/ PressAnnouncements/ 2008/ ucm116960.htm.). The maximum residue level of melamine in infant formula is now legally regulated at 1 ppm by the Chinese government after the recent melamine accident (Guo et al, 2010). To achieve this lower limit of detection (LOD), silver colloids are ideal candidates to be used as surfaced-enhancing substrate liquid sensors due to their strong Raman-enhancing effect.…”

Sensitive fluorescent detection of melamine in raw milk based on the inner filter effect of Au nanoparticles on the fluorescence of CdTe quantum dots

“…The second red-shifted plasmon absorption originates from the aggregation of AuNPs when the individual nanoparticles are electronically coupled to each other (Link and El-Sayed, 1999). As shown in Scheme 1, melamine could strongly bind to the surface of AuNPs through the amine group by the ligand exchange with citrate ions, and the ligand exchange decreases the electrostatic repulsion between individual AuNPs and finally results in the aggregation of AuNPs (Guo et al, 2010;Li et al, 2010). Besides, the neighbor melamine-coated AuNPs could be cross-linked by NHÁ Á ÁN hydrogen bonds between melamine molecules, thereby inducing the aggregation of AuNPs .…”

“…Therefore, the fluorescence emission of CdTe QDs centered at 553 nm, can be tuned by the melamine-AuNPs system via IFE, which provides a new strategy for fluorescent detection of melamine. In fact, the aggregation and corresponding color change of AuNPs driven by melamine have been employed for the visual sensing of melaimine in milk and infants (Guo et al, 2010;Li et al, 2010). These colorimetric techniques for the detection of melamine, however, generally display lower sensitivity.…”

“…Au and Ag nanoparticles (NPs) have been extensively used as colorimetric probes for melamine sensing in liquid milk and infant formula owing to their unique size-dependent and interparticle-distance dependent optical properties and the accompanying color change of solution (Guo et al, 2010;Li, Li, Cheng, & Mao, 2010;Ping et al, 2012). A sensitive turn-on fluorescent detection method for melamine has been developed through its modulation on the efficiency of fluorescence resonance energy transfer (FRET) between Au nanoparticles (AuNPs) and fluorescein (Guo et al, 2011).…”

“…The fluorescence of CdTe QDs is very weak in the presence of AuNPs due to the intensive absorption of AuNPs. In the presence of melamine, melamine would strongly bind to the surface of AuNPs through the amine groups by the ligand exchange with citrate ions (Guo et al, 2010;Li et al, 2010), rapidly inducing the aggregation of AuNPs, which thereby leads to the decreased absorption of AuNPs. As a result, the IFE-decreased emission of CdTe QDs is recovered, based on which melamine can be detected in a simple and sensitive approach.…”