Analytical methods and recent developments in the detection of melamine

Sixteen animals affected in 2 outbreaks of pet food-associated renal failure (2 dogs in 2004; 10 cats and 4 dogs in 2007) were evaluated for histopathologic, toxicologic, and clinicopathologic changes. All 16 animals had clinical and laboratory evidence of uremia, including anorexia, vomiting, lethargy, polyuria, azotemia, and hyperphosphatemia. Where measured, serum hepatic enzyme concentrations were normal in animals from both outbreaks. All animals died or were euthanized because of severe uremia. Distal tubular lesions were present in all 16 animals, and unique polarizable crystals with striations were present in distal tubules or collecting ducts in all animals. The proximal tubules were largely unaffected. Crystals and histologic appearance were identical in both outbreaks. A chronic pattern of histologic change, characterized by interstitial fibrosis and inflammation, was observed in some affected animals. Melamine and cyanuric acid were present in renal tissue from both outbreaks. These results indicate that the pet food-associated renal failure outbreaks in 2004 and 2007 share identical clinical, histologic, and toxicologic findings, providing compelling evidence that they share the same causation.

The color change induced by triple hydrogen-bonding recognition between melamine and a cyanuric acid derivative grafted on the surface of gold nanoparticles can be used for reliable detection of melamine. Since such a color change can be readily seen by the naked eye, the method enables on-site and real-time detection of melamine in raw milk and infant formula even at a concentration as low as 2.5 ppb without the aid of any advanced instruments.

In this article, we describe a disposable nucleic acid biosensor (DNAB) for low-cost and sensitive detection of nucleic acid samples in 15 min. Combining the unique optical properties of gold nanoparticles (Au-NP) and the high efficiency of chromatographic separation, sandwich-type DNA hybridization reactions were realized on the lateral flow strips, which avoid multiple incubation, separation, and washing steps in the conventional nucleic acid biosensors. The captured Au-NP probes on the test zone and control zone of the biosensor produced the characteristic red bands, enabling visual detection of nucleic acid samples without instrumentation. The quantitative detection was performed by reading the intensities of the produced red bands with a portable strip reader. The parameters (e.g., the concentration of reporter probe, the size of Au-NP, the amount of Au-NP-DNA probe, lateral flow membranes, and the concentration of running buffer) that govern the sensitivity and reproducibility of the sensor were optimized. The response of the optimized device is highly linear over the range of 1-100 nM target DNA, and the limit of detection is estimated to be 0.5 nM in association with a 15 min assay time. The sensitivity of the biosensor was further enhanced by using horseradish peroxidase (HRP)-Au-NP dual labels which ensure a quite low detection limit of 50 pM. The DNAB has been applied for the detection of human genomic DNA directly with a detection limit of 2.5 microg/mL (1.25 fM) by adopting well-designed DNA probes. The new nucleic acid biosensor thus provides a rapid, sensitive, low cost, and quantitative tool for the detection of nucleic acid samples. It shows great promise for in-field and point-of-care diagnosis of genetic diseases and detection of infectious agents or warning against biowarfare agents.