Melamine

On-site detection of sub-mg/kg melamine mixed in powdered infant formula and chocolate using sharp-edged gold nanostar substrates.[Pubmed:29727263]

Food Addit Contam Part A Chem Anal Control Expo Risk Assess. 2018 Jun;35(6):1017-1026.

We report a facile method for sample preparation and sensitive on-site detection of Melamine in powdered infant formula and chocolate using Raman spectroscopy on sharp-edged gold nanostars (AuNSs). The aggregation of AuNSs by sodium chloride (1.2 M) facilitates the more sensitive detection of Melamine in comparison with spherical gold nanoparticles (AuNPs). Density functional theory quantum mechanical calculations were performed to determine the energetic stability on gold cluster atoms. Our spectroscopic data indicated that AuNSs are an efficient platform for detecting Melamine in food mixtures. The detection limits of Melamine in powdered infant formula and chocolate were found to be ~0.1 mg/kg and ~1 mg/kg, respectively, on AuNPs, whereas they were observed to be ~0.01 mg/kg and ~0.1 mg/kg, respectively, on AuNSs. Using a handheld Raman spectrometer, a sub-mg/kg detection of Melamine in both powdered infant formula and chocolate could be achieved within a few minutes.

In situ synthesis of g-C3N4/TiO2 heterojunction nanocomposites as a highly active photocatalyst for the degradation of Orange II under visible light irradiation.[Pubmed:29725923]

Environ Sci Pollut Res Int. 2018 Jul;25(19):19122-19133.

As a highly active photocatalyst, g-C3N4/TiO2 heterojunction nanocomposites were in situ synthesized by simple ultrasonic mixing and calcination by using TiO2 and Melamine as precursors. The morphology and structure of the prepared photocatalysts were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, UV-Vis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. The photocatalytic activities of g-C3N4/TiO2 nanocomposites to degrade Orange II (AO7) under visible light irradiation were evaluated. Results showed that the photocatalytic rate of the prepared g-C3N4/TiO2 photocatalyst to degrade AO7 was about three times than that of pristine TiO2 and g-C3N4. The g-C3N4/TiO2 composite with a ratio of 1:4 had the highest degradation efficiency for AO7 solution. Its degradation efficiency under acidic conditions was significantly higher than that under alkaline conditions. The enhancement of photocatalytic activity can be attributed to the formation of heterojunctions between g-C3N4 and TiO2, which leads to rapid charge transfer and the efficient separation of photogenerated electron-hole pairs. The recycling experiment indicated that the photocatalyst of g-C3N4/TiO2 nanocomposites still maintained good photochemical stability and recyclability after five cycles; this finding was important for its practical applications. A series of free radical trapping experiments showed that *O2(-) played a crucial role in the degradation of AO7. Graphical Abstract .

Rapid, On-Site, Ultrasensitive Melamine Quantitation Method for Protein Beverages Using Time-Resolved Fluorescence Detection Paper.[Pubmed:29719144]

J Agric Food Chem. 2018 Jun 6;66(22):5671-5676.

To ensure protein beverage safety and prevent illegal Melamine use to artificially increase protein content, a rapid, on-site, ultrasensitive detection method for Melamine must be developed because Melamine is detrimental to human health. Herein, an ultrasensitive time-resolved fluorescence detection paper (TFDP) was developed to detect Melamine in protein beverages within 15 min using a one-step sample preparation. The lower limits of detection were 0.89, 0.94, and 1.05 ng/mL, and the linear ranges were 2.67-150, 2.82-150, and 3.15-150 ng/mL (R(2) > 0.982) for peanut, walnut, and coconut beverages, respectively. The recovery rates were 85.86-110.60% with a coefficient of variation <7.80% in the spiking experiment. A high specificity was observed in the interferent experiment. When detecting real protein beverage samples, the TFDP and ultraperformance liquid chromatography-tandem mass spectrometer (UPLC-MS/MS) results were consistent. This method is a promising alternative for rapid, on-site detection of Melamine in beverages.

A New Synthesis Approach for Carbon Nitrides: Poly(triazine imide) and Its Photocatalytic Properties.[Pubmed:29732448]

ACS Omega. 2018 Apr 30;3(4):3892-3900.

Poly(triazine imide) (PTI) is a material belonging to the group of carbon nitrides and has shown to have competitive properties compared to melon or g-C3N4, especially in photocatalysis. As most of the carbon nitrides, PTI is usually synthesized by thermal or hydrothermal approaches. We present and discuss an alternative synthesis for PTI which exhibits a pH-dependent solubility in aqueous solutions. This synthesis is based on the formation of radicals during electrolysis of an aqueous Melamine solution, coupling of resulting Melamine radicals and the final formation of PTI. We applied different characterization techniques to identify PTI as the product of this reaction and report the first liquid state NMR experiments on a triazine-based carbon nitride. We show that PTI has a relatively high specific surface area and a pH-dependent adsorption of charged molecules. This tunable adsorption has a significant influence on the photocatalytic properties of PTI, which we investigated in dye degradation experiments.

Detection of melamine in milk powder using MCT-based short-wave infrared hyperspectral imaging system.[Pubmed:29718763]

Food Addit Contam Part A Chem Anal Control Expo Risk Assess. 2018 Jun;35(6):1027-1037.

Extensive research has been conducted on non-destructive and rapid detection of Melamine in powdered foods in the last decade. While Raman and near-infrared hyperspectral imaging techniques have been successful in terms of non-destructive and rapid measurement, they have limitations with respect to measurement time and detection capability, respectively. Therefore, the objective of this study was to develop a mercury cadmium telluride (MCT)-based short-wave infrared (SWIR) hyperspectral imaging system and algorithm to detect Melamine quantitatively in milk powder. The SWIR hyperspectral imaging system consisted of a custom-designed illumination system, a SWIR hyperspectral camera, a data acquisition module and a sample transfer table. SWIR hyperspectral images were obtained for Melamine-milk samples with different Melamine concentrations, pure Melamine and pure milk powder. Analysis of variance and the partial least squares regression method over the 1000-2500 nm wavelength region were used to develop an optimal model for detection. The results showed that a Melamine concentration as low as 50 ppm in Melamine-milk powder samples could be detected. Thus, the MCT-based SWIR hyperspectral imaging system has the potential for quantitative and qualitative detection of adulterants in powder samples.

Assembly of Hollow Carbon Nanospheres on Graphene Nanosheets and Creation of Iron-Nitrogen-Doped Porous Carbon for Oxygen Reduction.[Pubmed:29722961]

ACS Nano. 2018 May 22.

Triblock copolymer micelles coated with Melamine-formaldehyde resin were self-assembled into closely packed two-dimensional (2D) arrangements on the surface of graphene oxide sheets. Carbonizing these structures created a 2D architecture composed of reduced graphene oxide (rGO) sandwiched between two monolayers of sub-40 nm diameter hollow nitrogen-doped carbon nanospheres (N-HCNS). Electrochemical tests showed that these hybrid structures had better performance for oxygen reduction compared to physically mixed rGO and N-HCNS that were not chemically bonded together. Further impregnation of the sandwich structures with iron (Fe) species followed by carbonization yielded Fe1.6-N-HCNS/rGO-900 with a high specific surface area (968.3 m(2) g(-1)), a high nitrogen doping (6.5 at%), and uniformly distributed Fe dopant (1.6 wt %). X-ray absorption fine structure analyses showed that most of the Fe in the nitrogen-doped carbon framework is composed of single Fe atoms each coordinated to four N atoms. The best Fe1.6-N-HCNS/rGO-900 catalyst performed better in electrocatalytic oxygen reduction than 20 wt % Pt/C catalyst in alkaline medium, with a more positive half-wave potential of 0.872 V and the same limiting current density. Bottom-up soft-patterning of regular carbon arrays on free-standing 2D surfaces should enable conductive carbon supports that boost the performance of electrocatalytic active sites.

Fluorescence detection of melamine based on inhibiting Cu(2+)-induced disaggregation of red-emitting silver nanoclusters.[Pubmed:29742485]

Spectrochim Acta A Mol Biomol Spectrosc. 2018 Aug 5;201:112-118.

Herein, we report a facile method to synthesize red-emitting, water-soluble Ag nanoclusters (Ag NCs) employing lipoic acid as a stabilizing agent. The Ag NCs show aggregation-induced emission property and have good stability and optical properties. Cu(2+) can disperse the aggregated Ag NCs, accompanied by the quenching of fluorescence. However, the formed Cu(2+)-Melamine complex by the coordination chemistry between free copper ion and Melamine is able to effectively avoid the quenching process of Cu(2+) to the Ag NCs. Hence, the Ag NCs can be applied to design a novel fluorescent probe based on this property to detect Melamine. In the determination of Melamine, the as-prepared fluorescent Ag NCs exhibit favorable sensitivity and high selectivity. The limit of detection (LOD) down to 0.022mg/L and good recoveries of real sample experiments were obtained. This fluorescent probe is proved to be convenient and rapid for detecting Melamine, with potential application to trace Melamine analysis in complicated samples.

Rapid and selective DNA-based detection of melamine using alpha-hemolysin nanopores.[Pubmed:29701202]

Analyst. 2018 May 15;143(10):2411-2415.

We have developed a rapid and selective approach for the detection of Melamine based on simple DNA probes and alpha-hemolysin nanopores. The limit of detection can be as low as 10 pM.