Detection Of Melamine Research Articles

Synthesis and Characterisation of Alginate Functionalized Gold Nanoparticles for Melamine Detection

Synthesis and Characterisation of Alginate Functionalized Gold Nanoparticles for Melamine Detection

Naked-Eye Optical Recognition of Ammonia Vapor and Melamine in Water Using a Fluorophore Appended Polymer Matrix.

The generation of solid-state emitters is a challenge due to the intrinsic aggregation-caused quenching feature of the fluorophores. A conformationally twisted pyridyl π-conjugate as a solid-state emitter is appended with well-known and inexpensive poly(methylmethacrylate) [PMMA] to afford a handy, portable, and reusable solid-state emitting polymer matrix. Entrapment of the probe is noticed through non-covalent interactions, resulting in a green-emitting platform. It quickly accepts a proton upon acid vapor exposure and switches emission from green to red with a significant 107nm redshift. This shift is reversible with red to green emissions while exposed to base vapor. Thus, polymer-blended, homogeneous red-emitting pyridyl salt is employed as potential material to detect various basic vapors optically. Among different bases, naked-eye detection of essential analytes such as ammonia vapor and melamine shows potential demands. Hence, we have established an easy detection of ammonia vapor and aqueous melamine as low as 2.5 and 0.126ppm, respectively, using this solid-state emitter that displays an emission color change with an enhancement of emission intensity even in an aqueous solution.

Centrifugation assembly proceeded tube-based SERS sensor for field-deployable solution detection

A novel tube-based SERS sensor is proposed to simplify the SERS fabrication and achieve field-deployable detection via a successive process of in-situ synthesis of Ag-NPs solution, centrifugal assembly of Ag-NPs film and separation-free detection of complex matrix, which offers the outstanding advantages of user-friendly operation, easy integration, and mass production. The high-density Ag-NPs are uniformly assembled on the inner surface of centrifuge tube, providing large amounts of SERS hotspots to enlarge the high sensitivity for targeted molecules. The tube-based sensor exhibits ultrahigh sensitivity with an average enhancement factor of 8.7 × 107, and improved reproducibility with a relative signal deviation down to 3.92%. Based on the tube-based sensor, the field-deployable rapid detection of thiram and melamine added in milk can be directly realized without any pretreatment. Therefore, the demonstrated portable and cost-effective tube-based SERS sensors offer promising potentials for field-deployable detection in environmental monitoring and food safety.

Ag Nanoparticles@Agar Gel as a 3D Flexible and Stable SERS Substrate with Ultrahigh Sensitivity.

Flexible surface-enhanced Raman scattering (SERS) substrates have become one of the research hot spots due to the facile sampling by swabbing or wrapping on rough surfaces and the sensitive and nondestructive detection of contaminants. In this work, we proposed a simple and fast in situ reduction method to prepare Ag nanoparticles (Ag NPs) composited agar hydrogel (Ag NPs@Agar) flexible SERS substrate. Owing to the three-dimensional (3D) structure, good hydrophilicity and adsorption of the agar hydrogel, Ag NPs were grown uniformly in the 3D cross-linked structure. The distribution density of Ag NPs was further increased by the volume shrinkage when the hydrogel was dried in air. This high density and uniformly distribution of Ag NPs produced a large number of highly active SERS regions. In addition, the sensitivity of Ag NPs@Agar was further improved with the assistance of hydrophilic agar gel, which can trap the probe molecules into highly active SERS areas. The SERS results showed that the substrate can be used to detect dye molecules (rhodamine 6G), the minimum detectable concentration was 10-15 M, the relative standard deviation tested at 18 different positions was only 7.58%, and the intensity of the characteristic peak at 611 cm-1 decreased only about 10% after 49 days of storage, demonstrating the superior stability. Moreover, the Ag NPs@Agar substrate also could successfully achieve the micro-trace detection of melamine and sodium penicillin G in Xinjiang specialty camel milk powder. The above available results show that the prepared flexible Ag NPs@Agar SERS substrates possess potentials for the illegal additives and antibiotics in food safety analysis.

A novel CRISPR/Cas14a1-Exo III aptasensor for melamine detection coupled with systematically studied binding mechanism of truncated aptamer

In this work, the aptamer of melamine was truncated and mutated. Based on isothermal titration calorimetry, circular dichroism and molecular dynamics, the thermodynamic information, structural changes and binding pocket of the truncated aptamer SJs32 with 32 bases to melamine were systematically studied. Meanwhile, a novel aptasensor coupled with CRISPR/Cas14a1 and Exo III was developed for melamine detection. SJs32 was first hybridized with the complementary DNA (cDNA) to form SJs32-cDNA. In the presence of melamine, SJs32 recognized melamine to form SJs32-melamine and performed structural transformation, which resulted in the releasing of cDNA into the solution. Exo III digested the SJs32-melamine and the released melamine led to the dissociation of more cDNA from SJs32-cDNA complex. Finally, the combination of cDNA and sgRNA activated the trans-cleavage activity of Cas14a1. According to the change of fluorescence intensity, the sensitive and rapid detection of melamine was realized with the linear detection range of 4 nmol/L-1 µmol/L. The developed strategy broadened the application of melamine aptamer in food safety and provided a new insight for the development of CRISPR/Cas14a1 aptasensor.

Application of 2D-COS-FTIR spectroscopic analysis to milk powder adulteration: Detection of melamine

Milk and its products are important and widely traded food commodities, which made them the target for adulteration. Fourier Transform Infrared spectroscopy (FTIR) is one of the most widely used methods to identify chemical contaminations and determine their concentrations. In the present work, two-dimensional correlation spectroscopy (2D-COS) was applied to analyse FTIR spectra of milk powder having different concentration of melamine. With the help of sequential order analysis, the FTIR band at 815 cm −1 was determined as the most qualified FTIR band for carrying quantitative analysis. It is recommended to perform 2D-COS and determine the sequential order of intensity change among all peaks of the contamination. This is to establish the appropriate bands for quantitative analysis, and help to improve the values of analytical parameters. • FTIR spectrum of milk powder was examined for melamine adulteration. • 2D-COS-FTIR and the sequential analysis were used to determine a quantitative band. • The band at 815 cm −1 was the most qualified band for quantitative analysis. • The proposed method is particularly important when dealing with new adulterations. • FTIR combined with 2D-COS are powerful tools in milk powder adulteration.

H2O2-assisted detection of melamine using fluorescent probe based on corn cob carbon dots-Ionic Liquid-Silver nanoparticles

In this work, a new sustainable melamine detection method was developed. Biomass-derived carbon dots (CDs) were successfully prepared by ionic liquid (1-Allyl-3-methylimidazolium chloride, IL) hydrothermal method using agricultural waste corn cob as the carbon source, and combined with silver nanoparticles (AgNPs) to construct fluorescent probe CDs@IL-AgNPs. The probe was characterized and the formation mechanism of the probe was discussed. The direct detection of H2O2 and the indirect sensitive detection of melamine were realized. The detection limit of melamine was 0.94 μmol/L, which is far lower than the minimum allowable amount of melamine in milk powder (7.95 μmol/L). The high sensitivity and selectivity probe was used to detect melamine in commercial dairy products, and the recovery rate of standard addition was between 94 % and 110 %. This study provides valuable new application ideas for the detection of melamine in dairy products and the low-carbon and environmentally friendly treatment of agricultural waste.

A Molecularly Imprinted Polymer-Based Thermal Sensor for the Selective Detection of Melamine in Milk Samples.

In recent years, melamine-sensing technologies have increasingly gained attention, mainly due to the misuse of the molecule as an adulterant in milk and other foods. Molecularly imprinted polymers (MIPs) are ideal candidates for the recognition of melamine in real-life samples. The prepared MIP particles were incorporated into a thermally conductive layer via micro-contact deposition and its response towards melamine was analyzed using the heat-transfer method (HTM). The sensor displayed an excellent selectivity when analyzing the thermal response to other chemicals commonly found in foods, and its applicability in food safety was demonstrated after evaluation in untreated milk samples, demonstrating a limit of detection of 6.02 μM. As the EU/US melamine legal limit in milk of 2.5 mg/kg falls within the linear range of the sensor, it can offer an innovative solution for routine screening of milk samples in order to detect adulteration with melamine. The results shown in this work thus demonstrate the great potential of a low-cost thermal platform for the detection of food adulteration in complex matrices.

A self-assembly hydrophobic oCDs/Ag nanoparticles SERS sensor for ultrasensitive melamine detection in milk

A simple, ultra-sensitive, and super-stable hydrophobic SERS platform for detection of melamine in milk is developed. The hydrophobic SERS platform was constructed via directly growing hydrophobic carbon/silver nanoparticles on glass by in-situ one-step carbonization using hexadecylpyridinium chloride monohydrate as stabilizer and reducing agent. The performances of SERS platform are systematically studied by using Rhodamine 6G (R6G) as a model, which achieves detection level of 10−13 M and enhancement factor of 3.4 × 1010 for R6G detection with good uniformity and reproducibility, as well as 110 days stability in air. The FDTD simulation was used to confirm SERS enhancement mechanism. More importantly, SERS platform delivers good linear property in the range from 0.01 to 100 ppm, and low limit detection of 9 ppb for melamine detection in milk through direct drop on the platform. The SERS platform could have great applications in food safety, environmental monitoring, biomedicine and other fields.

Detection of melamine by using carboxyl-functionalized Ag-COF as a novel SERS substrate

Melamine, a nitrogen-containing organic molecule, has received widespread attention as it had been illegally added in dairy products to increase the content of nitrogen, leading to kidney stones in healthy people after long-term ingestion. Based on SERS technology and Covalent Organic Framework (COF) materials, we developed carboxyl-functionalized Ag-COF-COOH materials as SERS substrates for the detection of melamine adulteration. Using COF material as a ligand can effectively reduce the influence of interferents in milk. In addition, we investigated two causes of melamine SERS enhancement: the ordered arrangement of Ag NPs and the strong interaction between the substrate and the melamine. The linear range was 1–20 μg/L and the limit of detection (LOD) was 0.68 μg/L in liquid milk due to the high sensitivity and reliability of this method. The results show that this new SERS substrate has great potential for applications in the food surveillance industry.

Two-step aggregation of gold nanoparticles based on charge neutralization for detection of melamine by colorimetric and surface-enhanced Raman spectroscopy platform.

A colorimetric and surface-enhanced Raman scattering (SERS) signal amplification platform based on 2-step aggregation of gold nanoparticles (AuNP) was constructed for the sensitive detection of melamine. In this study, the positively charged SYBR Green I was used for the first step of aggregation of AuNP, via charge neutralization, to obtain small-sized AuNP aggregates. The positively charged SYBR Green I decreased the negative charges of the surface of AuNP, which was beneficial to the aggregation of AuNP. In addition, the melamine could aggregate AuNP by decreasing the negative charges of the surface of AuNP and self-assemble with each other on the surface of AuNP by hydrogen bonds. Therefore, the second efficient aggregation of small-sized AuNP aggregates could be achieved with melamine at low concentration, resulting in significant signal changes of color and SERS. The sensitivity of a colorimetric (0.60 mg/L) and SERS (0.089 mg/L) platform, based on 2-step aggregation of AuNP, was 15 and 2.2 times higher than that based on 1-step aggregation of AuNP for detecting melamine.

DNA hydrogels combined with microfluidic chips for melamine detection

The illegal addition of melamine (MEL) into pet foods and infant milk powder has caused great concern among people. In this study, a point-of-care testing (POCT) method was developed by combining stimuli-responsive deoxyribonucleic acid (DNA) hydrogels with microfluidic chips to achieve portable and sensitive detection of MEL. With the MEL aptamer (MA) acting as a cross-linker, DNA hydrogel-coated gold nanoparticles (AuNPs) served as a basis for colorimetric detection and quantitative analysis. In the presence of MEL, it competitively binds to the aptamer, causing disintegration of the DNA hydrogels and a release of the coated AuNPs, making it possible to visually detect and quantitatively measure the MEL. Under optimal conditions, the detection range of MEL using DNA hydrogels was 0.1–100 μM and the limit of detection (LOD) was 42 nM. This portable, sensitive, and user-friendly field test equipment was developed to avoid the use of non-portable laboratory instruments. Furthermore, we combined microfluidic chips with the properties of DNA hydrogels, making it possible to quantitatively detect MEL by taking photos and analyzing the gray value using software in accordance with the different colors of copolymerization solutions after the reaction. The detection range of MEL using the microfluidic chip-based method was 0.2–50 μM, and the LOD was 37 nM. Neither trained operators nor large-scale instruments are needed for using this method to conduct portable and sensitive field detection of the targets, which highlights the methods excellent potential in food security, clinical tests, environmental monitoring, and other aspects.

An efficient and low-cost surface-enhanced fluorescence substrate for trace detection of melamine in milk samples

ObjectiveSurface-enhanced fluorescence (SEF) technology has wide application potential in the food security field. In this paper, an efficient and low-cost biological SEF substrate is designed for the trace detection of melamine in milk. MethodsThe substrate uses an easy to operate and stable magnetron sputtering system to modify the metal nanomaterials on lotus leaf (L.l.) surface(size: (1 cm × 1 cm). The SEF substrate (L.l.@Ag-25) with the best enhancement effect was selected by rhodamine 6 G (R6G), and the enhancement mechanism of fluorescence was analyzed by theoretical simulation. ResultThe filamentous structure on surface of L.l. was modified by metallic nanomaterials to form nanoparticles producing a good local surface plasmon resonance (LSPR) effect. There are high-density “hot spots” on L.l.@Ag-25 substrate, which generate strong electromagnetic fields and effectively enhance the fluorescence intensity of probe molecules. The L.l.@Ag-25 substrate has a low detection limit of 0.01 mg/L for melamine in milk samples, which is much lower than national detection standard. SignificanceThis filamentous structure of L.l surface provides a new strategy to the design and construction of SEF substrates, and establises potential application of detecting harmful substances in real environment,which has a good practical value.

Multiamperometric-SERS detection of melamine on gold screen-printed electrodes

• New multiamperometric-SERS detection method for analysis. • SERS substrates electrochemically prepared in few seconds. • Simple and reproducible methodology for SERS substrates preparation. • Good figures of merit for melamine determination. A new, simple and fast protocol to generate gold-based SERS substrates is presented in this work. Melamine is a compound widely used in the industry that can be toxic for humans if consumed even in low concentrations. EC-SERS is an excellent alternative to classical methods to detect and quantify this compound because Raman spectroscopy provides a fingerprint of the molecules, providing very good sensitivity. In this work, time-resolved Raman spectroelectrochemistry is employed to generate a SERS substrate and to detect melamine, all in a single experiment. The dynamic character of this technique provides valuable information about the interaction of the molecule with the generated substrate. An optimization of the spectroelectrochemical method based on a multi-pulse amperometric detection has been performed. The new protocol presented in this work shows significant figures of merit in a very short experiment time, just 25 s.

Multiplexed surface-enhanced Raman scattering detection of melamine and dicyandiamide in dairy food enabled by three-dimensional polystyrene@silver@graphene oxide hybrid substrate

Owing to its ultranarrow spectral line width, surface-enhanced Raman scattering (SERS) as a specific fingerprint identification technology has exhibited its distinctive talent in the multiplexed assay of illegal food additives. Herein, a three-dimensional (3D) hybrid SERS substrate was constructed by utilizing polystyrene (PS) nanospheres as template matrix, silver as active interlayer, and graphene oxide (GO) as coating surface to enable the effective monitoring of mixed melamine and dicyandiamide in dairy food without interference. Through amalgamating the significant electromagnetic effect triggered by the PS-mediated 3D architectures with the chemical enhancement and molecule-enrichment abilities of GO, the proposed substrate exhibited a highly sensitive detection characteristics with reliable reproducibility, facilitating a limit of detection low to 2.8 × 10−8 M for 2-naphthalenethiol. After the further establishment of standard calibration lines, the feasibility of the proposed sensitive substrate in the multivariate monitoring of melamine and dicyandiamide was verified in milk as well as yogurt, achieving moderate recovery rates higher than 75%. This work proposed a facile strategy to construct 3D hybrid SERS substrate, which might show great promise to secure food security.

Gold nanoparticle based colorimetric and Raman “turn-off” sensing of melamine in milk

Here, we report the development of a sensitive colorimetric and Raman “turn-off” sensor based on gold nanoparticles (AuNPs), for the detection of melamine (MM) in real milk samples. The methodology relies on the effect of analyte-reducer interaction on the formation and stabilization of AuNPs. Gallic acid (GA), used as the reducing and capping agent imparts size and shape control to the AuNPs. In aqueous solution as well as milk extracts, the size control of AuNPs was found to be affected with increase in the concentration of analyte (MM). This resulted in the colour variation of the AuNPs solution from red to purple to blue and grey. The increasing size of AuNPs with higher MM concentration also resulted in Raman “turn-off” sensing due to the reduced effect of surface plasmon. From the least square fit of relative absorbance versus MM concentration, the limit of detection (LOD) was found to be ~1.15 ppb, which is lower than the WHO recommended limit of 1 ppm. This methodology for on-site visual colorimetric detection and Raman “turn-off” sensing involves ultra-filtration technique for the extraction of MM from milk matrix. The developed methodology is simple, rapid and cost effective. This study can thus, be further exploited for the development of low cost, robust colorimetric sensors for industrial use.

Development of jellyfish-like ZnO@Ag substrate for sensitive SERS detection of melamine in milk

Melamine has received enormous attention because of being illegally adulterated into milk, posing potential threats to human health. It is vital for developing sensitive analytical methods for detecting melamine in milk at the lowest possible concentration. In this context, we proposed a highly sensitive surface-enhanced Raman scattering (SERS) substrate based on hybridization of jellyfish-like zinc oxide microparticles and silver nanoparticles (JF ZnO@Ag) for detecting melamine in milk. The JF ZnO with a rough surface facilitates the deposition of Ag nanoparticles and adsorbing analytes, providing the abundant “hot spots” for the electromagnetic enhancement and the suitable charge transfer path to induce the chemical enhancement. Using the rhodamine 6G (R6G) as the Raman probe, the enhancement factor is as high as 7.58 × 106. As a real application, the substrate was successfully utilized in the detection of melamine in milk. The limit of detection (LOD) was down to 0.098 ppm, which is lower than the safety limit in the USA (2.5 ppm). The results manifest that the proposed substrate is an effective strategy to be applied as an analytical platform for the efficient detection of melamine in milk.

Melamine-imprinted electrochemical sensor of graphene/ionic liquid composites and its use for the detection of melamine in dairy products

• Melamine-imprinted electrochemical sensor • Molecularly imprinted polymer • Dairy products supervision • Graphene/ionic liquid compound modification By exchanging the conventional role of functional monomer and template molecules, we develop a new molecularly imprinted nanospheres with grape grain structures based on multi-hydrogen bonding interactions between melamine and 6-aminouracil. Molecular imprinting-electrochemical sensor was established with the assistance of graphene and ionic liquids. The content of melamine in dairy products was detected by the molecular imprinting-electrochemical sensor. The detection limit was determined to be as low as 1.57 × 10 −3 mg kg -1 .

Development of an ultrasensitive molecularly imprinted poly-(ortho-phenylenediamine) based sensor for the determination of melamine adulteration in milk and infant formula.

A sensitive molecularly imprinted poly‐(ortho‐phenylenediamine) electrochemical sensor was fabricated for selective melamine detection in milk and infant formula. The pencil graphite electrode (PGE) was modified by deposition of Au nanoparticles and reduced graphene oxide (RGO) on its surface. The fabrication of the electrode in various stages was monitored using cyclic voltammetry. The immobilized RGO, MIP, and gold nanoparticles on the PGE surface were morphologically characterized by field‐emission scanning electron microscopy (FESEM). Under the optimized conditions, the linear range and the limit of detection (LOD) were 10–17–10–8 M and 2.64 × 10–16 M (S/N = 3), respectively. The prepared sensor exhibited a good reproducibility and repeatability response. The recovery range of melamine‐spiked milk and infant formula was 92.7%–103.9% and 93.5%–105.8%, respectively. The sensor could apply successfully for melamine determination in milk and infant formula samples.

Background-free room temperature phosphorescence and digital image colorimetry detection of melamine by carbon nitride quantum dots in cellulose matrix with smartphone-based portable device

Carbon nitride quantum dots (CNQDs) were embedded in the sodium carboxymethyl cellulose (CMC) matrix to form CNQDs-CMC film to explore the room temperature phosphorescence (RTP) of CNQDs, which suppress the non-radiative relaxation process due to the internal hydrogen bonding interactions between CMC and CNQDs. Then, a simple, inexpensive, background-free miniature device integrating with CNQDs-CMC film and smartphone was fabricated for rapid and quantitative detection of melamine (MEL). In the present of MEL, the yellow RTP color of the CNQDs-CMC film was quenched and photographed by the smartphone. The Color Recognizer APP in the smartphone recognized the red (R) value for quantitative detection of MEL. Thus, digital image colorimetry (DIC) determination of MEL was achieved due to the visible RTP color change of CNQDs-CMC film. The smartphone-based miniature device provided a promising platform for the on-site monitoring analytes in the complex matrix including food safety, environmental screening, health monitoring, and disease prevention.