Detection Of Melamine Research Articles

Target detection of melamine in wheat gluten in a NIR infrared hyperspectral image

Hyperspectral imaging is continuing to gain popularity in a wide variety of applications in chemical sensing, standoff sensing and remote sensing. One area of particular interest for hyperspectral imaging in the food, pharmaceutical and chemical industries is detection of trace particulates in feedstocks and raw materials. The reason for this interest is that hyperspectral imaging is well suited for detection of minor signals in heterogenous samples. In these cases, the concentration of an analyte to be detected can have a very low concentration on a volume basis but can dominate the signal in a single hyperspectral imaging pixel. This article discusses the use of a target detection strategy for detection of trace particulates of melamine in wheat gluten.

Rational design of an allosteric G-quadruplex aptamer probe for ultra-sensitive detection of melamine in milk

Efficient and accurate detection of melamine in dairy products remains a crucial yet challenging task. Herein, an allosterically modulated G-quadruplex-integrated aptamer is rationally designed with thymine-rich recognition termini for melamine binding. The detection process is facile by simply introducing the analyte into the mixture consisting of G-quadruplex aptamer probes, exonuclease III, and thioflavin T (ThT). The detection feasibility is confirmed by the polyacrylamide gel electrophoresis and fluorescence measurement results. This exonuclease III-assisted signal amplifiable approach works well in a linear range from 0.1 nM to 0.1 μM. Moreover, a detection limit as low as 83 pM is easily achieved, which is almost five orders of magnitude smaller than the maximum allowable melamine levels (about 8 μM) defined by many countries all over the world. The whole assay time for each test is no longer than 1 h. Additionally, the scheme is highly specific and satisfactory recovery rates (from 91% to 104%) are readily obtained when challenged with melamine-spiked milk samples. Therefore, the label-free, turn-on, low-cost, and time-efficient method can be used for reliable detection of melamine in an easily manipulated and ultra-sensitive manner, which may find its utilization in the field of food safety, biomedical engineering, and clinical diagnosis.

Graphene Oxide-Coated Metal-Insulator-Metal SERS Substrates for Trace Melamine Detection.

Surface-enhanced Raman spectroscopy (SERS) has long been an ultrasensitive technique for trace molecule detection. However, the development of a sensitive, stable, and reproducible SERS substrate is still a challenge for practical applications. Here, we demonstrate a cost-effective, centimeter-sized, and highly reproducible SERS substrate using the nanosphere lithography technique. It consists of a hexagonally packed Ag metasurface on a SiO2/Au/Si substrate. A seconds-lasting etching process of a self-assembled nanosphere mask manipulates the geometry of the deposited Ag metasurface on the SiO2/Au/Si substrate, which attains the wavelength matching between the optical absorbance of the Ag/SiO2/Au/Si substrate and the excitation laser wavelength as well as the enhancement of Raman signals. By spin-coating a thin layer of graphene oxide on the substrate, a SERS performance with 1.1 × 105 analytical enhancement factor and a limit of detection of 10−9 M for melamine is achieved. Experimental results reveal that our proposed strategy could provide a promising platform for SERS-based rapid trace detection in food safety control and environmental monitoring.

A simplified fluorescent lateral flow assay for melamine based on aggregation induced emission of gold nanoclusters

A novel lateral flow assay (LFA) was developed based on the aggregation induced emission (AIE) of gold nanoclusters (AuNCs) for the detection of melamine. We compared the interaction between melamine and AuNCs prepared with 6-Aza-2-thiothymine (ATT) and its four structural analogs as ligands and found that the ATT-AuNCs showed the best AIE induced by melamine. Then the ATT-AuNCs were directly immobilized on the test line of LFA strips as reporters. The sensing platform exhibited a linear response to melamine from 1 to 100 μM (R2 = 0.997) with a detection limit of 217 nM. Moreover, this LFA strip could discriminate 1.0 μM melamine clearly by the naked eyes within 3 min. The recoveries of 91.6–101.5% were attained in milk and baby formula samples. This strip inherited the superior characteristics of low background interference of aggregation-induced fluorescence recognition and LFA technology, thus effectively avoiding the use of antibodies, aptamers, and other biological elements.

A unique supramolecular assembly between sulfated cyclodextrin, silver and melamine: Towards a fluorescence based dual wavelength detection approach for melamine

Nitrogen-rich melamine has been often used by fraudulent merchants as an adulterant to food and dairy products which exhibit toxic effects, leading to life-threatening diseases. This has triggered enormous activity on developing methods for the recognition of melamine in various food items for protecting public health and food safety. In recent times, fluorescence methods have emerged as powerful analytical tools for sensor development. The previously reported fluorescence-based methods for melamine detection, either require tedious synthesis procedures or operate through single wavelength-based signal output, making their accuracy susceptible to minute changes in the experimental environment. Herein, to overcome these limitations, we report the recognition of melamine which is achieved through the formation of a serendipitously discovered unique supramolecular assembly. The assembly consists of sulfated cyclodextrin, silver ion and melamine which, in turn, encapsulates a molecular rotor dye, Thioflavin-T, to yield a fluorescence turn-on response towards melamine. Importantly, the supramolecular assembly is responsive at dual wavelengths and is builtup with all commercially available economical molecules. Overall, the present system offers a simple, sensitive, label-free and highly selective detection for melamine. Importantly, the melamine containing supramolecular ensemble is also found to perform in commercial milk sample promising its future application prospect.

One step construction of an electrochemical sensor for melamine detection in milk towards an integrated portable system

Excessive intake of melamine (MEL) can be harmful to human health, and it is important to establish a rapid and accurate MEL detection method. As the electrochemical activity of MEL is very low, ferrocenylglutathione (Fc-ECG) was used as an electron transfer mediator to assist with the detection of MEL using screen-printed carbon electrode (SPCE). This modified electrode (MEL/Fc-ECG/SPCE) was prepared by stepwise drop-casting and was fully characterized. Results showed that MEL significantly enhanced signal of Fc-ECG/SPCE sensor due to the three p-π conjugated double bonds that facilitated electron transfer. Under optimal conditions, the sensor exhibits two linearities in the range of 0.20–2.00 μM and 8.00–800 μM, with a sensitivity of 15.03 μA·μM−1·cm−2. The selectivity, stability, and reproducibility were investigated and successfully used to detect MEL in raw milk and confirms safety verification of foods. Moreover, a portable testing platform was designed for MEL detection based on a CH32 chip.

Molecular Imprinting With Polyaniline on ENIG Finish PCB Electrodes for Electrochemical Detection of Melamine

Electrochemical sensors based on molecularly imprinted polymers (MIPs) leverage predetermined recognition sites (templates) for binding of analytes of interest, resulting in high selectivity and sensitivity, ease of preparation and portability. The choice of monomers and cross-linkers depends heavily on choice of substrate for in situ electropolymerization, and damage to the template caused by methods used to wash away the analyte after formation of MIP on the substrate result in limitations for batch-compatible synthesis methods of such sensors. In this paper, we describe a method to utilize low-cost ENIG finish PCB electrodes as electrochemical sensor substrates for detection of melamine, a common adulterant in milk, through molecular imprinting in polyaniline (PANI). The MIP was synthesized using chemical synthesis method and drop-casted onto the electrodes, thus realizing a low-cost fabrication method. Preliminary results for melamine detection are reported, along with performance evaluation of various synthesis methods to synthesize polyaniline.

High and stable surface-enhanced Raman spectroscopy activity of h-BN nanosheet/Au1Ag3 nanoalloy hybrid membrane for melamine determination

In this work, a hexagonal boron nitride (h-BN)/AuAg nanoalloy hybrids (NAHs) was synthesized to fabricate h-BN/Au1Ag3 membrane as a solid surface-enhanced Raman spectroscopy (SERS) substrate for sensitive SERS detection of melamine. The AuAg nanoalloys were in situ grown on h-BN by chemical reduction method, and the Au/Ag molar ratio was tuned to achieve optimal SERS performance. After the SERS performance of h-BN/AuAg NAHs with different Au/Ag ratios was analyzed, h-BN/Au1Ag3 NAHs were chosen for SERS analysis. The h-BN/Au1Ag3 membrane can be obtained through simple filtration of h-BN/Au1Ag3 NAHs on chromatographic paper. As expected, the solid SERS substrates of h-BN/Au1Ag3 membrane were uniform and demonstrated good selectivity, repeatability and reproducibility for SERS detection of melamine. The results demonstrate that h-BN/Au1Ag3 membrane exhibited high SERS activity for 4-mercaptobenzoic acid (4-MBA) with limit of detection (LOD) at 1.0 ng L−1, and its analytical enhancement factor (AEF) reached 3.6 × 108. The possible enhancement mechanism, including electromagnetic mechanisms (EM) and chemical mechanisms (CM) were illustrated by finite-difference time-domain (FDTD) and density functional theory (DFT) simulations in detail, respectively. The concentration of melamine in the 0.05–5.0 mg L−1 range showed good linear relationship (R2 = 0.9940) with SERS intensity with LOD of 0.01 mg L−1. Finally, the recoveries of melamine in liquid milk samples are 87.7–105.7% with relative standard deviations (RSDs) in range of 0.6–2.6%, providing precise safety evaluation of melamine in milk samples.

Construction and Signal Feature Processing of Gold Nanobiosensors Based on the Internet of Things.

With the continuous development of signal amplification technology and nanotechnology, more and more electrochemical sensors combining nanotechnology and signal amplification technology are applied in the field of analysis. In this paper, combined with the Internet of Things technology, the construction of gold nanobiosensors and signal characteristic processing are carried out. In this paper, a T-rich DNA probe is used as the recognition element, modified on the electrode surface, combined with DNA-modified nanogold particle amplification technology, and the electroactive substance peg amine is used as the signal molecule to develop a highly sensitive electrochemical biosensor for the detection of melamine. The sensor has good specificity and sensitivity, and the detection limit is as low as 0.5 NM. In addition, by combining sensors with the Internet of Things technology, melamine monitoring and signal characteristic processing can be carried out in real time. This model can easily achieve the purpose of accurate and quantitative analysis of melamine toxins and can be effective for food safety.

Highly efficient peroxidase-like activity of a metal-oxide-incorporated CeO2-MIL(Fe) metal-organic framework and its application in the colorimetric detection of melamine and mercury ions via induced hydrogen and covalent bonds.

The illegal addition of melamine to dairy products and the contamination of water with mercury (Hg2+) are serious threats to human health. Hence, herein, a highly sensitive colorimetric sensor for the visual detection of melamine and Hg2+ ions has been developed using a metal-oxide-in-MOF nanomaterial (CeO2-MIL (Fe)) as a peroxidase mimic. Highly mono-dispersed CeO2-MIL (Fe) was synthesised via a facile hydrothermal process. The CeO2-MIL (Fe) exhibited outstanding peroxidase activity, and can catalyze the oxidation of TMB (3,3',5,5'-tetramethylbenzidine) by H2O2, resulting in the development of blue-coloured oxidation products within 5 min. In the presence of melamine, the H2O2 interacts with melamine to form melamine-H2O2via H-bonding. Due to the uptake of H2O2 by melamine, the catalytic oxidation reaction was halted, and the blue TMB oxidation product became pale. The relative change in the absorption intensity at 652 nm was proportional to the concentration of melamine in the linear range of 0-0.1 μM and the detection limit was found to be 8 nM. Subsequently, when Hg2+ ions were added to the above solution, the Hg2+ ions reacted with melamine via strong covalent bonding to form a Hg2+-melamine covalent complex, causing the release of H2O2, which again strongly oxidised the TMB to give the blue-coloured oxidation product. Furthermore, the comparative change in the absorption intensity at 652 nm was dependent on the concentration of Hg2+ ions in the linear range of 0-6 nM, and a detection limit of 2 nM was achieved. The suggested system has several advantages including greater simplicity, good selectivity, naked-eye detection and cost-effectiveness without using any complicated detection procedure. This technique was successfully utilized to identify melamine in real foods and Hg2+ ions in real water samples, yielding high recovery rates.

Determination of four melamine and its derivatives in urine by ultra-performance liquid chromatography-tandem mass spectrometry

To establish a method for simultaneous detection of melamine(MEL), ammeline(AMN), ammelide(AMD) and cyanuric acid(CYA) in urine by ultra-performance liquid chromatography-tandem mass spectrometry(UPLC-MS/MS). After the urine sample was added to the internal standard, they were mixed by acetonitrile, ultrasonic extraction and centrifugation, enriched by MCX or MAX solid phase extraction column, eluted with 5% ammoniated methanol or 2% formic acid methanol, dried under nitrogen at 40 ℃, separated by Amide chromatography column(2.1 mm×100 mm, 1.7 μm), qualitatively and quantitatively analyzed by mass spectrometer in the simultaneous scanning mode of positive and negative ions. Melamine and its derivatives were completely separated with great chromatography peak. The limit of detection(LOD) for melamine, ammeline, ammelide and cyanuric acid were 0.03, 0.04, 0.04 and 0.05 ng/mL, and the limit of quantification(LOQ) were 0.11, 0.12, 0.14 and 0.15 ng/mL, respectively. The recovery rate of standard addition samples of 0.2, 5, 50 and 200 ng/mL ranged from 94.6% to 106.5%, the intra-day precision was between 0.73% and 8.34%, and the inter-day precision was less than 6.80%(n=6). At low concentrations, AMD and CYA mainly showed matrix enhancing effect, while AMN showed matrix inhibitory effect with increasing concentration. The overall detection rate of melamine and its derivatives was 75.0% in 60 parcels of random urine. The average concentration of urinary melamine and its derivatives were higher in men. UPLC-MS/MS can simultaneously determine four melamine and its derivatives in urine. The LOD and LOQ of the current method were low with great accuracy and precision.

Dual fluorometric biosensor based on a nanoceria encapsulated metal organic framework and a signal amplification strategy of a hybridization chain reaction for the detection of melamine and Pb2+ ions in food samples

The increased need for melamine and Pb2+ ion detection systems that are versatile, ultra-sensitive, and easy to use is highly significant.

A Fluorescence-Based Chemical Sensor for Detection of Melamine in Aqueous Solutions

Melamine, an industrial chemical, receives wide attention nowadays because of its unethical usage as a nitrogen enhancer in protein-rich foods and dairy products. Since most of the existing melamine detection methods are highly expensive and time-consuming, high sensitivity biosensor-based detection methods have arisen in the scientific literature as promising alternatives. This study reports the design, synthesis, and fluorescent investigations of a carbazole-based sensor (CB) for the detection of melamine in aqueous solutions. The titration studies and microplate experiments on a CB-cyanuric acid mixture (CB-CA) with melamine suggested that the novel sensor could detect melamine even at very low concentrations in both aqueous solutions and dairy samples.

Sensitive SERS detection of melamine and cyromazine in raw milk using aptamer-based in situ silver nanoparticles synthesis

In this paper, we develop a simple design for simultaneous detection of melamine (MEL) and cyromazine (CYR) by surface-enhanced Raman scattering (SERS) with the formation of well-defined MEL or CYR-aptamer-AgNPs. This detection will take only 10 min, and SERS signals generated by MEL-aptamer-AgNPs exhibits a linear dependence on melamine (R2 = 0.998) concentration ranging from 0.1 to 0.5 ppm on melamine. The detection limit is sensitive down to 43.5 ppb. SERS signals generated by CYR-aptamer-AgNPs exhibits a linear dependence on cyromazine (R2 = 0.997) concentration ranging from 0.1 to 0.5 ppm on cyromazine. The detection limit is sensitive down to 23.6 ppb. This SERS biosensor was first reported for the simultaneous detection of melamine and cyromazine by using aptamer-based in situ silver nanoparticles synthesis. So we expected that the development of this biosensor could provide a good platform for the rapid detection of other pollutants in raw milk.

Hierarchical Chiral Supramolecular Nanoarchitectonics with Molecular Detection: Helical Structure Controls upon Self-Assembly and Coassembly.

The morphological transformation from microspheres to helical supramolecular nanofibers with controllable handedness is achieved by the introduction of molecular chirality based on amino acid derivatives (TDAP), and the chirality of the supramolecular architectures that are achieved is nullified through the coassembly of the equivalent TDAP enantiomers. The molecular detection of achiral melamine based on the R-TDAP-COOH supramolecular system is achieved by the appearance of helicity and inversion.

Construct high-precise SERS sensor by hierarchical superhydrophobic Si/Cu(OH)2 platform for ultratrace detection of food contaminants

Construction of the high-quality noble metal nanoparticle cluster (NMNPC) with big size for surface-enhanced Raman spectrum is still a challenge nowadays, due to its difficulty in integration of the uniformity, repeatability and sensibility. To realize this goal, a superhydrophobic platform composed of hierarchical Si/Cu(OH)2 nanowires with stable Cassie state was designed and prepared in this work. The optimal Ag NPC region is larger than 0.6 mm × 0.6 mm, and the limit of detection and relative standard deviation of it are respectively 2 × 10−18 M and 13.85%, indicating the fine SERS performance of it. Finite difference time domain simulations and systematic experimental analysis were made in detail here to figure out the underlying mechanism behind these phenomena. Furthermore, as a proof of concept, the Ag NPC was proved as an outstanding food contaminant sensor and successfully realized an ultratrace detection of both melamine in milk and malachite green on fish surface (ca 10−15 M, approaching to single-molecule level). This work provides a new way in constructing high-performance SERS substrate and shows promising application prospect in food safety inspection.

Highly sensitive and selective detection of melamine in dairy products by turn-on fluorescence of ultrathin graphitic carbon nitride nanosheets.

There is an important and realistic need to develop a practical sensor for melamine in dairy products that is highly sensitive and selective. However, the complicated composition and environment in milk necessitate the use of a stable luminophore as the sensor, as well as excellent photophysical properties. Here, ultrathin graphitic carbon nitride nanosheet (CNNS) was prepared by successive thermal polymerization and acid exfoliation. The photophysical properties of CNNS include its strong ultraviolet absorption and intense blue-light emission. Notably, CNNS could act as a chemo-sensor to detect trace melamine in dairy products. The high stability, eminent sensitivity, powerful selectivity, and competitiveness all substantiate the findings that this CNNS luminophore is a promising sensor for melamine in dairy products, and has potential practical value for monitoring milk quality.

The creation of selective imprinted cavities on quartz crystal microbalance electrode for the detection of melamine in milk sample

Molecularly imprinted polymer based nanofilms specific to melamine were synthesized on quartz crystal microbalance (QCM) electrode surface. Contact angle measurements, atomic force microscopy, ellipsometry and scanning electron microscopy were used for characterizations process. Some of the findings of the study are as follows: pH 6.0 was found as optimal working pH for melamine detection. Prepared MIP QCM electrode showed a linearity of 99.53% in the concentration range of 50–1000 ng/mL. Langmuir-Freundlich hybrid model was the best fitted isotherm for whole concentration range. The performance of MIP QCM electrode was also confirmed by determining of melamine in melamine spiked milk samples. As a conclusion, the results figured out that not only QCM nanosensor for specific melamine detection but also polymerization strategy were classified as an intriguing alternative for developing new melamine sensing platforms. Limit of detection (LOD) and limit of quantification (LOQ) were calculated as 2.3 ng/mL and 7.8 ng/mL, respectively.

Development of metal free melamine modified graphene oxide for electrochemical sensing of epinephrine

Metal free material melamine modified graphene oxide (MGO) was prepared by reacting melamine with graphene oxide followed by thermal annealing process. The prepared material was characterized by a range of microscopic and spectroscopic techniques. It was then applied for the detection of epinephrine at a biological pH. An MGO-modified GCE displayed improved electrocatalytic activity by shifting the anodic peak current negatively by 0.1193 V and the cathodic peak current positively by −0.2311 V, compared to those at the GCE. Density Functional Theory (TD-DFT method) was used to predict the electron transfer (ET) sites of MGO. The limit of detection of melamine at the MGO -modified glassy carbon electrode was estimated to be 0.13 µM which indicated the potential application of the electrode to the biosensing of the neurotransmitter epinephrine.

Fabrication of the cerium dioxide@carbon quasi-aerogels for anti-interference detection of melamine

Improper addition of melamine in milk powder poses a threat to human health, but the interference of complex components makes the trace detection hard. The cerium dioxide@carbon quasi-aerogels (CeO2@C-QAs) with Schottky barrier was successfully prepared to detect melamine in milk powder. The interfacial effects of Schottky barrier on electrochemical detection are studied and find energy barrier can be used as a novel electrochemical driving factor to achieve anti-interference sensing. The highly sensitive detection of melamine was achieved at acidic and alkaline environments. It obtained the good recovery rate and exhibited anti-interference in real milk powder detection. The lowest detection limit (2.19 nM) was much lower than the international safety threshold of melamine content. It affords an inspiring chance to achieve anti-interference electrochemical detection by using the interfacial energy barrier effects.