Melamine Concentration Research Articles

Colorimetric determination of melamine in milk using unmodified silver nanoparticles

Melamine is nitrogen rich chemical compound used as an adulterant in dairy products by unscrupulous people to increase the apparent protein content. This incident prompted the researchers to develop simple methods for easy detection of melamine in food samples. In the present paper, we report a simple and sensitive colorimetric method for detection of melamine in milk based on silver nanoparticles. This method relies upon the principle that melamine causes the aggregation of silver nanoparticles, resulting in abrupt color change from yellow to red under optimized conditions. The concentration of melamine in adulterated sample can be quantitated by monitoring the absorption spectra of silver nanoparticles using ultraviolet–visible (UV–Vis) spectrometer. The present colorimetric method which utilizes silver nanoparticles of 35nm can reliably detect melamine down to a concentration of 0.04mgl−1.

Melamine Alters Glutamatergic Synaptic Transmission of CA3-CA1 Synapses Presynaptically Through Autophagy Activation in the Rat Hippocampus.

Melamine is an industrial chemical that can cause central nervous system disorders including excitotoxicity and cognitive impairment. Its illegal use in powdered baby formula was the focus of a milk scandal in China in 2008. One of our previous studies showed that melamine impaired glutamatergic transmission in rat hippocampal CA1 pyramidal cells. However, the underlying mechanism of action of melamine is unclear, and it is unknown if the CA3-CA1 pathway is directly involved. In the present study, a whole-cell patch-clamp technique was employed to investigate the effect of melamine on the hippocampal CA3-CA1 pathway in vitro. Both the evoked excitatory postsynaptic current (eEPSC) and the paired-pulse ratio (PPR) were recorded. Furthermore, we examined whether autophagy was involved in glutamatergic transmission alterations induced by melamine. Our data showed that melamine significantly increased the amplitude of eEPSCs in a dose-dependent manner. Inhibition of the N-methyl-D-aspartic acid receptor did not prevent the increase in eEPSC amplitude. In addition, the PPR was remarkably decreased by a melamine concentration of 5×10(-5)g/mL. It was found that autophagy could be activated by melamine and an autophagy inhibitor, 3-MA, prevented the melamine-induced increase in eEPSC amplitude. Overall, our results show that melamine presynaptically alters glutamatergic synaptic transmission of hippocampal CA3-CA1 synapses in vitro and this is likely associated with autophagy alteration.

Broiler chickens exposed to melamine and cyanuric acid-contaminated diets.

The objective of this study was to investigate whether melamine (MEL) is biotransformed into cyanuric acid (CYA) in male broiler chickens. The effects of the dietary addition of MEL and CYA alone and in combination on the growth performance and mortality of the chickens were also investigated. The chickens were divided into six experimental groups and were fed diets with an addition of 50 or 100 mg/kg MEL or 50 or 100 mg/kg CYA of diet, with the contaminants added separately or in combination. The control group was fed a diet without MEL or CYA. At the end of the experiment (day 40), samples of liver, kidney and breast and thigh muscles were collected from 12 birds per treatment group and were analysed for the presence of MEL and CYA. This study showed that MEL is biotransformed into CYA in broilers. Higher concentrations of MEL or CYA in the diet increased the presence of their residues in tissues, and the CYA residue concentration was several times higher in the respective tissues than the MEL residue concentration. The dietary addition of MEL and CYA did not affect the mortality rate, feed conversion ratio or body weight of the chickens.

<i>In Vitro</i> Degradation of Melamine by Ruminal Microorganisms

An in vitro study was conducted to determine the extent of melamine degradation in rumen liquor. Rumen liquor was collected from two ruminally cannulated Holstein cows on four separate dates, one week apart. Erlenmeyer flasks (250 mL) were prepared for incubation by adding 1000 mg of a dairy feed substrate, 100 mg melamine and 100 mL incubation medium, purged with CO 2 and fitted with rubber stoppers equipped with one-way gas release valves. The initial melamine concentration was thus 1000 mg/L. The substrates consisted of 600 mg of a commercial dairy concentrate, 200 mg lucerne hay and 200 mg oat hay. The incubation medium consisted of 19 mL rumen liquor, 77 mL of Van Soest buffer and 4 mL of a reducing solution. The flasks were incubated at 39 oC for 0, 6, 24 or 48 hours (two flasks per time in each of four replicates). The 0 h incubation served as a control treatment to enable the calculation of melamine recovery values. For the control treatment (0 h), fermentation was terminated at the onset of the trial by aerating the rumen liquor and submerging the flasks in 50 mm ice. On termination of the incubation, 100 mL 0.2 M perchloric acid was added to each flask in order to dissolve any undegraded melamine. Melamine concentrations were determined by liquid chromatography-tandem mass spectrometry. Melamine degradation was low after 6 hours and 24 hours of incubation (3.2% and 5.5%, respectively) and increased to 13.6% after 48 h of incubation. It was concluded that melamine has low degradability in rumen liquor. Keywords: Non-protein Nitrogen, Rumen Fermentation, Rumen Incubation

Portable Detection of Melamine in Milk Using a Personal Glucose Meter Based on an in Vitro Selected Structure-Switching Aptamer.

Melamine detection in milk and other foods has attracted much attention since the discovery that melamine-adulterated food causes severe kidney damage. Although many methods have been developed to detect melamine, few methods can provide quantitative results using an affordable and portable device that is suitable for home use or field application. To achieve this goal, we herein report the first in vitro selection of a melamine responsive aptamer using a structure-switching method. A personal glucose meter (PGM) based melamine sensor was designed and subsequently tested using the newly isolated aptamer. Conversion of melamine concentration to glucose amount was achieved by including an invertase-conjugated DNA that is complementary to part of the aptamer. Melamine binding triggers the release of the invertase-DNA conjugate, which hydrolyzes sucrose into glucose. The glucose produced is then measured directly using an off-the-shelf PGM. The described sensor shows high selectivity for melamine against several closely related melamine analogues, such as cyanuric acid, ammeline, and ammelide, and has low detection limits of 0.33 μM (or 41.1 ppb) in buffer and 0.53 μM (or 67.5 ppb) in 80% whole milk without any pretreatment. The detection limits meet the threshold of 2.5 ppm for non-infant-formula products and 1 ppm for melamine in infant milk products as defined by the U.S. Food and Drug Administration (FDA). In addition to the PGM sensor demonstrated here, the same aptamer can be converted into other types of sensors with different signal outputs, allowing portable detection of melamine under a variety of conditions.

Electrochemical sensor based rapid determination of melamine using ionic liquid/zinc oxide nanoparticles/chitosan/gold electrode

Melamine is an organic base and a triazine of cyanamide with a 1,3,5-triazine skeleton. It contains 67% a nitrogen by mass. It is introduced as a contaminant in food products with the intent to falsify total protein content. The illegal adulteration of infant milk powder with melamine has resulted in chronic kidney and urinary tract failure. To date, several analytical methods have been developed for the detection of melamine. However, the existing methods are complicated, time consuming and costly. There is an urgent need to develop a simple, fast and effective method for the analysis of melamine in infant milk and milk products. For that reason, an novel electrochemical method was developed based on an ionic liquids (1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM][Otf])), zinc oxide nanoparticles (ZnONPs) with chitosan (CHIT), and the modified gold electrode (AuE). Methylene blue was used as a redox indicator for increasing the electron transfer in electrochemical cell. The electrochemical behaviour of the modified gold electrode was studied by using cyclic voltammetry and differential pulse voltammetry at the presence of melamine. The morphological characteristics were observed under scanning electron microscope and transmission electron microscope. The electrochemical sensor showed an optimal response within 30 s, pH 7.0 and 0.3 V. Under optimal conditions, differential pulse voltammetry was detected a wide linear range of melamine concentrations from 9.6 × 10−4 to 9.6 × 10−13 M, with a detection limit 9.6 × 10−14 M. The linear regression equation for the calibration plot was calculated to be y = 0.4239x + 6.6686 (r2 = 0.9836), where x is the concentration of melamine and y is the oxidation current. The proposed method is fast and simple procedure technique for analysing the melamine level in milk powder products.

Poly thymine stabilized copper nanoclusters as a fluorescence probe for melamine sensing

In this work, poly-thymine stabilized copper nanoclusters have been used as a fluorescence probe for melamine sensing for the first time. Melamine can bind to thymine through hydrogen bond, which could dramatically enhance the fluorescence intensity of poly-thymine stabilized copper nanoclusters. The enhancement factors (I−I0)/I0 increase linearly with the lgCmelamine over the melamine concentration range of 0.1µM to 6µM. The detection limit of melamine is 95nM, which is 200 times lower than the US Food and Drug Administration estimate melamine safety limit 20µM. Melamine in milk was detected with good recovery, which suggested that this novel fluorescence probe has great potential in practical application.

Electrochemiluminescence sensor for melamine based on a [formula omitted]-doped silica nanoparticles/carboxylic acid functionalized multi-walled carbon nanotubes/Nafion composite film modified electrode

In this work, a sensitive electrochemiluminescence (ECL) sensor for the determination of melamine (MEL) was developed based on a Ru(bpy)32+-doped silica nanoparticles (RUDS)/carboxylic acid functionalized multi-walled carbon nanotubes (CMWCNTs)/Nafion composite film modified electrode. The homogeneous spherical RUDS were synthesized by a reverse microemulsion method. As Ru(bpy)32+ were encapsulated in the RUDS, Ru(bpy)32+ dropping from the modified electrode can be greatly prevented, which is helpful for obtaining a stable ECL signal. Moreover, to improve the conductivity of the film and promote the electron transfer rate on electrode surface, CMWCNTs with excellent electrical conductivity and large surface area were applied in the construction of the sensing film. As CMWCNTs acted as electron bridges making more Ru(bpy)32+ participate in the reaction, the ECL intensity was greatly enhanced. Under the optimum conditions, the relative ECL signal (△IECL) was proportional to the logarithmic MEL concentration ranging from 5×10−13 to 1×10−7molL−1 with a detection limit of 1×10−13molL−1. To verify the reliability, the thus-fabricated ECL sensor was applied to determine the concentration of MEL in milk. Based on these investigations, the proposed ECL sensor exhibited good feasibility and high sensitivity for the determination of MEL, promising the applicability of this sensor in practical analysis.

Determination of melamine in food contact materials using an electrode modified with gold nanoparticles and reduced graphene oxide

We describe an electrochemical sensor for melamine based on a glassy carbon electrode (GCE) modified with reduced graphene oxide that was decorated with gold nanoparticles (AuNP/rGO). The AuNPs/rGO nanocomposite was synthesized by co-reduction of Au(III) and graphene oxide and characterized by transmission electron microscopy, Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The response of the modified GCE to melamine was investigated by using hexacyanoferrate as an electrochemical reporter. It is found that the electrochemical response to hexacyanoferrate is increasingly suppressed by increasing concentration of melamine. This is attributed to competitive adsorption of melamine at the AuNP/rGO composite through the interaction between the amino groups of melamine and the AuNPs. The presence of rGO, in turn, provides a platform for a more uniform distribution of the AuNPs and enhances the electron transfer rate of the redox reaction. The findings were used to develop a sensitive method for the determination of melamine. Under optimized conditions, the redox peak current of hexacyanoferrate at a working voltage of 171 mV (vs. SCE) is linearly related to the concentration of melamine in 5.0 to 50 nM range. The method was successfully applied to the determination of melamine in food contact materials.

Ambient Melamine Exposure and Urinary Biomarkers of Early Renal Injury.

Information about environmental exposure to melamine and renal injury in adults is lacking. We investigated this relationship in 44 workers at two melamine tableware manufacturing factories in Taiwan (16 manufacturers, eight grinders, ten packers, and ten administrators) and 105 nonexposed workers (controls) at one shipbuilding company who were enrolled in August-December of 2012. For melamine workers, personal and area air samples were obtained at the worksite over 1 workweek (Monday-Friday). In the same week, pre- and post-shift one-spot urine samples were collected each workday and one first-spot urine sample was collected on each weekend morning and the following Monday morning. For each control, a one-spot urine sample was collected on Friday morning. A blood sample was also obtained from each participant at this time. Melamine levels were measured in air, urine, and serum, and early renal injury biomarkers were measured in urine. Urinary melamine concentrations in manufacturers increased sharply between pre- and post-shift measurements on Monday, remained significantly elevated throughout the workweek, and decreased over the weekend; changes in urinary melamine concentrations were substantially lower for other melamine workers. Manufacturers were exposed to the highest concentrations of ambient melamine and had significantly higher urinary and serum melamine concentrations than did the controls (P<0.001). Urinary melamine levels were positively associated with urinary N-acetyl β-d-glucosaminidase (NAG) levels but not microalbumin levels, and the detectable β2-microglobulin rate increased in the manufacturers group. In conclusion, ambient melamine exposure may increase the levels of urinary biomarkers of renal tubular injury in this occupational setting.

Molecularly imprinted electrochemical sensor for the highly selective and sensitive determination of melamine.

A selective and sensitive molecularly imprinted electrochemical sensor was developed for the determination of melamine. Carbon nanotube-ionic liquid composite was used as a carrier to enhance the number of imprinted cavities and then improve the selectivity and sensitivity of the sensor. The proposed sensor showed a linear relationship with the concentration of melamine in the range of 0.4 to 9.2 μM, with a detection limit of 0.11 μM. The sensor was successfully applied to the determination of melamine in milk products with good recovery.

Determination of melamine in milk and dairy products by microchip-based high-field asymmetric ion mobility spectrometry combined with solid-phase extraction

This article presents a method for sensitive, fast and quantitative determination of melamine in milk and dairy products using high-field asymmetric ion mobility spectrometry (FAIMS). The solid-phase extraction (SPE) technology was used for purification after the sample was extracted by organic solvents, and followed by the analysis of FAIMS. The measurement parameters and variables that affect the FAIMS detection have been investigated, and optimum conditions have been obtained as follows: the carrier gas flow rate is 1.6Lmin−1, the headspace sampler temperature is 150°C, the pressure is 1atm, and the humidity is 2.0gm−3. The results showed that the SPE–FAIMS method can detect melamine in samples with a concentration down to 0.1mgkg−1. The ion intensity has a linear relationship with melamine concentration in the range from 0.3mgL−1 to 25mgL−1, with a good linearity of 0.9975. The limits of detection (LOD) and limits of quantification (LOQ) are 0.1mgkg−1 and 0.3mgkg−1 in milk and dairy products, respectively, and the relative standard deviation is less than 8.0%. The results demonstrated that FAIMS has great potential as a powerful tool for food analysis and safety inspection.

Simultaneous enzymatic and SERS properties of bifunctional chitosan-modified popcorn-like Au-Ag nanoparticles for high sensitive detection of melamine in milk powder

In this work, we suggest a chitosan-modified popcorn-like Au–Ag nanoparticles (CSPNPs) based assay for high sensitive detection of melamine, in which CSPNPs not only provide with an intrinsic peroxidase-like activity but also act as surface enhanced Raman scattering (SERS) substrates. CSPNPs can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2 to the charge transfer complex (CTC), which contributes to a tremendous surface-enhanced resonant Raman scattering (SERRS) signals with 632.8nm laser excitation. The target molecule melamine can generate an additional compound with H2O2, which means the available amount of H2O2 for the oxidation of TMB reduced. Correspondingly, the SERRS intensity of CTC is decreased. The decreased Raman intensity is proportional to the concentration of melamine over a wide range from 10nM to 50μM (R2=0.989), with a limit of detection (LOD) of 8.51nM. Moreover, the proposed highly selective method is fully capable of rapid, separation-free detection of melamine in milk powder.

Room-temperature phosphorescence determination of melamine in dairy products using l-cysteine-capped Mn-doped zinc sulfide (ZnS) quantum dots

A simple, sensitive, and precise room-temperature phosphorescence method was developed for the determination of melamine in dairy products using l-cysteine-capped Mn-doped zinc sulfide (ZnS) quantum dots as a probe. This method is based on the quenching of the phosphorescence signal of quantum dots by the interaction with melamine. Under optimum conditions, phosphorescence intensity was quenched by various concentrations of melamine in a linear range from 50 to 500ng/mL, with a detection limit of 5.95ng/mL in 10 mM phosphate buffer (pH 7.4). The relative standard deviation for 5 replicate measurements was 0.15%. The developed method was applied to dairy products to determine melamine concentrations; recovery values ranged from 96.3 to 104.7%.

3D silver nanoparticles decorated zinc oxide/silicon heterostructured nanomace arrays as high-performance surface-enhanced Raman scattering substrates.

Three-dimensional (3D) hierarchical nanostructures have been considered as one of the most promising surface-enhanced Raman spectroscopy (SERS) substrates because of the ordered arrangement of high-density hotspots along the third dimension direction. Herein, we reported a unique 3D nanostructure for SERS detection based on silver nanoparticles (AgNPs) decorated zinc oxide/silicon (ZnO/Si) heterostructured nanomace arrays. They were prepared by two steps: (1) Si nanoneedles were grafted onto ZnO nanorod arrays via a catalyst-assisted vapor-liquid-solid (VLS) growth mechanism. (2) AgNPs were rapidly immobilized on the surface of nanomaces by a facile galvanic displacement reaction. The fabricated substrates were employed to detect rhodamine 6G (R6G) with a detection limit down to 10(-16) M, and exhibited a high-enhanced performance (enhancement factor (EF) as high as 8.7 × 10(7)). To illustrate the potential value of the prepared substrates, the different concentrations of melamine aqueous solution (from 10(-4) to 10(-10) M) were detected, and a quantitative relationship between the SERS spectrum intensity and the melamine concentration had been established. In addition, the measure of melamine residual in pure milk was carried out successfully, and the results indicated that the prepared 3D nanomace substrates had great potential in food inspection, environment protection, and a few other technologically important fields.

Development of melamine sensor based on ionic liquid/nanoparticles/chitosan with modified gold electrode for determination of melamine in milk product

The illegal adulteration of infant milk powder with melamine in China has resulted in chronic kidney and urinary tract failure in September 2008. To date, several analytical techniques have been used for the determination of melamine, although these techniques are complicated, time consuming and costly. In this study, we developed a novel electrochemical biosensor method based on the modification of gold electrode with chitosan, calcium oxide nanoparticles and an ionic liquid for the determination in the presence of melamine in milk products. The electrochemical behaviour of the modified gold electrode was studied by using cyclic voltammetry and differential pulse voltammetry in the presence of methylene blue used as a redox indicator. The morphological characteristics of nanomaterials were observed under scanning electron microscope. Under optimal conditions, differential pulse voltammetry was detected at different concentrations of melamine from 9.6×10−3 to 9.6×10−15M, with a detection limit of 9.6×10−16M. The developed melamine sensor method is a very simple and fast procedure for analysing melamine level in milk and milk products.

Effect of melamine toxicity on Tetrahymena thermophila proliferation and metallothionein expression

Melamine is a raw material in the chemical industry. Because of its high nitrogen content, melamine has been utilized by unscrupulous businessmen as a food additive to enhance the indices of protein content in food and feed testing. Tetrahymena has long been used as an excellent model organism in toxicological studies. The purpose of the present study was to determine the effect of melamine on Tetrahymena. In the present study, the effects of melamine on the proliferation and mating rate of Tetrahymena were examined by microscopic counting of the cell numbers. The comet assay and DAPI nuclear staining were performed to analyze the changes in the Tetrahymena genome. Flow cytometric analysis was conducted to detect apoptosis. Furthermore, RT-PCR was performed to determine the changes in the expression of the metallothionein gene in Tetrahymena that underwent stress treatment with varying concentrations of melamine. The results indicated that melamine affected the proliferation and sexual reproduction of Tetrahymena. High melamine concentrations damaged the Tetrahymena genome to a certain extent and induced apoptosis in the organism. Expression of the metallothionein gene was upregulated in Tetrahymena exposed to melamine stress to ameliorate melamine-induced damage. These results indicated that melamine displayed significant toxicity to Tetrahymena cells.

Fiber optic SPR sensor for the detection of melamine using molecular imprinting

Fabrication and characterization of a surface plasmon resonance based fiber optic sensor for the detection of melamine using molecular imprinting are reported. The probe is fabricated by coating a thin film of silver over the unclad core of an optical fiber which is further coated with the molecular imprinted (MIP) polymer using melamine as template molecule. The MIP layer creates binding sites, complementary of the template molecule on the surface. The template molecules have the capability to bind with these active sites. The performance of the sensor is tested for the melamine concentration range from 10−7M to 10−1M. A shift of 19nm in resonance wavelength is recorded for this concentration range. The sensitivity is maximized by optimizing melamine concentration in MIP layer formation and the pH of the sample solution. The selectivity of the probe is checked using different analytes and is found to be highly selective for melamine. The sensitivity of the sensor is improved by introducing a thin layer of aluminum between silver and MIP layer. The sensor has advantages of fast response, high selectivity and sensitivity, low cost and can be used for online monitoring and remote sensing applications.

More Health Hazards Are Expected if Melamine Wastes Are Allowed to Be Used as Fertilizers

The adulteration of milk with melamine in China in 2008 caused worldwide alarm over the use of unwanted chemicals in food. The melamine waste polluted the soil and this further resulted in health hazards. This study investigated the hazards of melamine wastes which are used as fertilizers. A cultivation experiment was designed to determine the contents of melamine in the plants and soil where melamine had been used as a fertilizer. The results showed that melamine detected in the first round of the harvested plants was 22.3 ± 4.8 ppm and that in the second round of the harvested plants it was 41.1 ± 16.7 ppm. In both of these situations the U.S.A.’s Food and Drug Administration’s (FDA) limit was exceeded. The soil residue contained a very high concentration of melamine, reaching a level of 235.1 ± 91.3 ppm. Melamine functions as a good fertilizer, comparable to urea. However, the plants absorbed the melamine, and the melamine content was higher than the level which is recommended as acceptable by the FDA. Our study supported the legitimate concern about melamine contamination in crops where melamine wastes have been used as a fertilizer. The toxic material remaining in the soil was a major concern. Keywords: Fertilizers, food contamination, hazardous waste, melamine.

An upconversion fluorescence resonance energy transfer nanosensor for one step detection of melamine in raw milk

Here we report a nanosensor based on fluorescence resonance energy transfer (FRET) between upconversion nanoparticles (UCNPs) and gold nanoparticles (AuNPs) for melamine detection. The positively charged UCNPs as donor and the negatively charged AuNPs as acceptor bound together through electrostatic interaction, which caused the fluorescence quenching of UCNPs. Upon addition of melamine, AuNPs were released from the surface of UCNPs and aggregation due to the N-Au interaction between melamine and AuNPs, which results in the fluorescence of UCNPs gradually recovered. Under the optimal conditions including media pH (7.0), the concentration of AuNPs (1.23nM) and incubation time (12min), the fluorescence enhanced efficiency shows a linear response to the melamine concentration ranging from 32.0 to 500nM with a detection limit of 18.0nM. Compared with other fluorescence methods, the fluorimetric nanosensor shows high sensitivity of 0.968, ease of operation and can be used for the determination of melamine in raw milk samples.