Detection Of Melamine In Milk Research Articles

Immunochromatographic assay for melamine based on luminescent quantum dot beads as signaling probes.

To screen and detect the harmful substance melamine (MEL), a quantum-dot-bead-based immunochromatographic assay (QB-ICA) was formulated. After optimization, calibration was performed within the linear range from 0.06 to 0.28 ng mL−1, with limit of detection (LOD) of 0.04 ng mL−1. The LOD was 35 times lower than that of ICA that used colloidal gold nanoparticles (LOD = 1.4 ng mL−1) and 40 times lower than that of the assay based on quantum dots (LOD = 1.6 ng mL−1). In the detection of MEL in spiked pure milk using the proposed QB-ICA strategy, the LOD (LOD = 0.19 ng mL−1) of the samples with the proposed pretreatment was 18.4 times lower than those of the samples without pretreatment (LOD = 3.5 ng mL−1). The performance and practicability of the proposed QB-ICA system was validated; the obtained results reveal that QB-ICA is comparable with the conventional enzyme-linked immunosorbent assay (ELISA) method, but with enhanced applicability. Given its high sensitivity and practicability, the QB-ICA strategy could become a worthwhile alternative for the rapid, sensitive, and quantitative onsite detection of harmful substances, facilitating food safety monitoring.

Colloidal silver-based lateral flow immunoassay for rapid detection of melamine in milk and animal feed

An immunosilver chromatographic strip based on a monoclonal antibody was developed for the detection of melamine (MEL) residues in milk and animal feed. Colloidal silver nanoparticles (AgNPs), of a diameter of approximately 10.4 nm, were surface-modified with trisodium citrate dehydrate (TSC) in order to improve their stability and dispersion. The anti-MEL monoclonal antibody (mAb) was successfully immobilized on the surface of AgNPs by ionic interactions and characterized using XRD, UV–Vis, TEM and XPS analyses. Surface modification of Ag-mAb conjugates with varying cross-reactivity and thermo-stability was employed to design and prepare labels for use in a lateral flow immunoassay (LFIA) to examine whether these factors affect the performance of the assay. The results showed that no cross-reactions with homologues cyanuric acid, ammeline or ammelide were found, and the test strip remained stable after storage for one year at room temperature. Under optimized conditions, a detection limit of 0.30 ppm for standard melamine was achieved, and limits of detection of 0.750 ppm and 0.875 ppm were obtained in milk and animal feed, respectively.

Aquamarine blue emitting silver nanoparticles as fluorescent sensor for melamine detection.

Designing an exceptional probe to detect minute quantities of melamine is of huge importance for the safety and health of the human race. In this study, an aquamarine blue and rapid fluorescent sensor was devised by chemical reduction synthesis method for highly selective and sensitive detection of melamine in milk using polyethyleneimine protected silver nanoparticles (PEI-AgNPs). The optical properties of PEI-AgNPs were studied as a function of reactive material concentration, incubation time, temperature and pH. The formation of PEI-AgNPs was verified by using transmission electron microscopy (TEM) and found that the PEI-AgNPs were spherical in shape with an average diameter of 15 nm. The prepared PEI-AgNPs were aquamarine blue luminescent under UV light and show a maximum emission at 470 nm, when excited at 348 nm. The fluorescence of the PEI-AgNPs can be effectively quenched by the addition of melamine due to its ability to interact with citric acid (CA) through hydrogen bonding and form silver-melamine complexes with Ag+ via coordination bonds, while the addition of other nitro compounds induced feeble quenching of PEI-AgNPs, suggesting the high selectivity of PEI-AgNPs. The present sensor system exhibits a good linear response to melamine ranging from 0.16 to 56 μM, and the limit of detection was found to be 132 nM (Sb/K = 3). Significantly, the fluorescence sensor exhibited good selectivity and acted as a potential probe for detection of melamine in milk samples.

Superhydrophobic 3D Forest‐Like Ag Microball/Nanodendrite Hierarchical Structure as SERS Sensor for Rapid Droplets Detection

AbstractReal environment detection application by surface‐enhanced Raman scattering (SERS) requires substrates with high sensitivity, rapid detection, and low cost. In this study, a rapid SERS detection of liquid droplets sample by a superhydrophobic 3D forest‐like Ag microball/nanodendrite hierarchical structure is reported. Easy preparation is provided by electrochemical deposition method, developing a Ag forest‐like hierarchical nanostructure. The vertically standing nanodendrites offer more amounts of SERS “hot spots” for enhancing the Raman signals. At the same time, the micro/nanostructures supply suitable condition for superhydrophobicity by low surface energy modification. Probe molecule droplets are directly detected by SERS on the substrate. Detection limit of crystal violet, methyl blue, and rhodamine 6G can be down to 10−8, 10−9, and 10−9 m, with good sensitivity and reproducibility. Practical application is processed for proving the utility of the substrate in real environment by quantitatively detection of melamine in milk. 0.1 ppm melamine in aqueous solution and 0.5 ppm melamine in milk can be detected by droplet detection method, which are far lower than the standard of US Food and Drug Administration. In brief, the droplet detection method offers an extensive and promising application in real life rapid trace detection.

Melamine-Mediated Base Mismatch for Label-Free and Amplified Sensitive Fluorescent Detection of Melamine in Milk

Sensitive identification and detection of melamine illegally added to food to increase false protein content is important for food safety monitoring because melamine can cause tissue injury or even death above the safety regulation level. Melamine can coordinate with two thymines to form stable T-melamine-T structures. On the basis of such a unique interaction, we have developed a T-melamine-T base mismatch-mediated rolling circle amplification (RCA) signal enhancement means for amplified sensitive and label-free fluorescent detection of melamine in milk. The presence of melamine facilitates the hybridization between two T:T base mismatch containing DNA strands, which triggers RCA generation of many long sequences with repeated G-quadruplex segments. The fluorescent dye, thioflavin T, further binds the resulting G-quadruplexes to exhibit substantially enhanced fluorescence for sensitive detection of melamine at the low nanomolar level in a label-free manner. Besides, the developed approach is highly selective toward the discrimination and detection of melamine in milk samples.

Preparation of DNA functional phosphorescent quantum dots and application in melamine detection in milk.

Bio-functionalization of quantum dots (QDs) is of important value in practical applications. With single-stranded DNA (ssDNA) rich in thymine T and thioguanine G taken as the template, a new-type nanocomposite material (ssDNA-PQDs) synthesized from low-toxicity T-ssDNA functionalized Mn–ZnS and room-temperature phosphorescent (RTP) QDs (PQDs) was prepared in this paper by optimizing synthesis conditions, and these ssDNA-PQDs could emit orange RTP signals at 590 nm. As these ssDNA-PQDs are rich in T sequences and T sequences can bond with melamine through the hydrogen-bond interaction, ssDNA-PQDs experience aggregation, thus causing phosphorescent exciton energy transfer (PEET) between ssDNA-PQDs of different particle sizes and their RTP quenching. Based on this principle, an RTP detection method for melamine was established. The linear range and detection limit of the detection method are 0.005–6 mM and 0.0016 mM respectively. As this method is based on the RTP nature of ssDNA-PQDs, it can avoid disturbance from background fluorescence and scattered light of the biological fluid, and it is very suitable for melamine detection in the biological fluid milk.

Bio-polyphenols promoted green synthesis of silver nanoparticles for facile and ultra-sensitive colorimetric detection of melamine in milk

Green, simple and quick melamine sensing assays for highly efficient detection of melamine down to nM level have been reported. Biopolyphenols (rutin & curcumin) were used as reducing and stabilizing agents for the synthesis of silver nanoparticles (AgNPs). The synthesis of AgNPs was confirmed by FTIR, UV–Visible, XRD and HRTEM-EDS analysis. The biopolyphenols reduced AgNPs were well dispersed and spherical in shape. However, the presence of melamine in the reaction medium disrupted their synthesis. This may be attributed to interaction of melamine with Ag+ ions and biopolyphenols. At low concentration of melamine, pale red colored solution was obtained owing to formation of aggregated mass of AgNPs, whereas, at high concentration of melamine, colorless solution was obtained indicating disruption in synthesis of AgNPs. The presented protocol was proposed in light of optical responses, UV–Visible plots and HRTEM-EDS analysis. Using the sensor assays, good limit of detection, 0.01 ppm (79 nM) and 0.24 ppm (1900 nM) by Ag-Rutin and Ag-Curcumin respectively, were obtained. The detection limits offered by both sensing assays were quite lower than safety level recommended by regulatory bodies (20 μM in the USA and EU, 8 μM for infant formula in China). The sensing assays displayed good selectivity as well as sensitivity. The proposed sensor was successfully deployed for detection of melamine in raw milk samples.

Use of a smartphone for visual detection of melamine in milk based on Au@Carbon quantum dots nanocomposites

Gold nanoparticles@Carbon quantum dots nanocomposites (Au@CQDs) were designed for analyzing melamine in milk visually. Fluorescent emission of Au@CQDs enhanced with the increase of melamine concentration. A calibration curve (R2 = 0.9856) and fluorescence standard array were established for detection of melamine in the range of 1 μM–10 μM. Limit of quantification and limit of detection were 12 nM and 3.6 nM, respectively. The approximate concentration of melamine adulterated in milk samples were detected visually by the fluorescence standard array and smartphone. The accurate concentration was obtained by the calibration curve and portable fluorescence spectrometer with recoveries of 105.64%–102.75% and less than 2% of coefficient of variation (CV) (n = 18). This performance was consistent with that of the high-performance liquid chromatography (HPLC) method (recoveries of 105.56%–107.95% with 2.24%–3.56% of CVs). The Au@CQDs-based fluorescent method for visual and accurate detection of melamine in milk was presented and showed strong application potential.

Sensitive detection of melamine by an electrochemiluminescence sensor based on tris(bipyridine)ruthenium(II)-functionalized metal-organic frameworks

Metal-organic frameworks (MOFs) are microporous materials that consist of metal ions or clusters and organic ligands. Their luminescence activities can be improved by functionalization, and the present work describes the synthesis of a luminescence-functionalized MOF in which tris(2,2′-bipyridyl) dichlororuthenium(II) hexahydrate (Ru(bpy)32+) was introduced into the MOF. The synthesized RuMOF was then fabricated as an ECL sensor that can be used for the rapid and sensitive detection of melamine in dairy products. The optimum detection conditions were established by single-factor analysis and surface response multivariate optimization. Under optimum conditions, the ECL intensity was proportional to log(melamine) concentration in the range 10−10–10−4 M with a detection limit of about 3.8 × 10−11 M (signal/noise = 3). In an application to the detection of melamine in milk and infant formula powder, recoveries in the range 98–104% and 95–103%, respectively were obtained from spiked samples. Thus this novel ECL sensor represents a potentially valuable product for the analysis of melamine food samples.

Aptamer-based detection of melamine in milk using an evanescent wave fiber sensor

Rapid detection of melamine has been achieved in past studies to support the quality control of milk and formula products.

Three‐dimensional MoS2‐NS@Au‐NPs hybrids as SERS sensor for quantitative and ultrasensitive detection of melamine in milk

AbstractMoS2, a novel inorganic graphene analogues with typical two‐dimensional structure, has attracted increasing interest in various fields. MoS2‐based hybrid plasmonic structures have been extensively investigated as higher quality surface enhanced Raman scattering (SERS) substrates. Herein, we have designed a three‐dimensional (3D) MoS2 nanospheres (NSs) based hybrid nanostructure as SERS sensor by decorating Au nanoparticles (NPs) on the surface of 3D MoS2‐NSs (3D MoS2‐NS@Au‐NPs). 3D MoS2‐NSs acts as (a) a stable scaffold for Au NPs decoration via microwave‐irradiation hydrothermal process, (b) a chemical mechanism source for Raman enhancement, and (c) a 3D spatial structure for generation of more effective hot spots due to Au coupling effect and supply larger surface area for adsorbing probe molecules. The 3D MoS2‐NS@Au‐NPs hybrid structure exhibits 56‐fold improvement on enhancement factor compared to two‐dimensional MoS2‐NST@Au‐NPs hybrid structures. SERS performance was easily and effectively optimized with the tuning of the density and sizes of Au NPs. The optimized 3D MoS2‐NS@Au‐NPs was applied as SERS sensor for melamine detection in milk. Quantitative detection was realized in the range of 1 ppb–10 ppm with a linear coefficient of .997. Excellent sensitivity of 1 ppb and uniformity of 10.12% relative standard deviation was achieved, which could meet the demand for melamine detection as prescribed by the U.S. Food and Drug Administration.

Colorimetric detection of melamine in milk based on Triton X-100 modified gold nanoparticles and its paper-based application

In this study, we have developed a method for rapid, highly efficient and selective detection of melamine. The negatively charged citrate ions form an electrostatic layer on gold nanoparticles (AuNPs) and keep the NPs dispersed and stable. When citrate-capped AuNPs were further modified with Triton X-100, it stabilized the AuNPs against the conditions of high ionic strength and a broad pH range. However, the addition of melamine caused the destabilization and aggregation of NPs. This may be attributed to the interaction between melamine and the AuNPs through the ligand exchange with citrate ions on the surface of AuNPs leading Triton X-100 to be removed. As a result, the AuNPs were unstable, resulting in the aggregation. The aggregation induced a wine red-to-blue color change, and a new absorption peak around 630nm appeared. Triton X-100-AuNPs could selectively detect melamine at the concentration as low as 5.1nM. This probe was successfully applied to detect melamine in milk. Furthermore, paper-based quantitative detection system using this colorimetric probe was also demonstrated by integrating with a smartphone.

Melamine Detection in Milk and Dairy Products: Traditional Analytical Methods and Recent Developments

Melamine is a nitrogen-rich compound (about 66%) whose fraudulent addition to foods aims to increase the apparent protein content. In 2008, melamine adulteration incidents occurred in China caused several deaths in humans from kidney failure and other health problems. This issue prompted private as well as governmental laboratories to develop several analytical methods in order to determine melamine in foods. This review aims to provide an overview of the analytical techniques currently available in the literature for melamine detection and measurement in milk and dairy products, including a specific section related to sample preparation. Recent studies concerning conventional (both screening and confirmatory) methods are reported, and technical and critical issues are discussed for each technique (liquid and gas chromatography, mass spectrometry, liquid chromatography coupled to mass spectrometry, gas chromatography coupled to mass spectrometry, and capillary electrophoresis). These techniques, very sensitive and specific but also time-consuming, may require tedious sample preparation, costly instrumentation, and skilled personnel. Therefore, new innovative detection methods are also provided, focusing attention on immunoassay, sensor technology, vibrational spectroscopy coupled to chemometrics, hyperspectral imaging, micellar liquid chromatography, magnetic resonance spectroscopy, and chemiluminescence.

Colorimetric detection of melamine in milk by using gold nanoparticles-based LSPR via optical fibers.

A biosensing system with optical fibers is proposed for the colorimetric detection of melamine in liquid milk samples by using the localized surface plasmon resonance (LSPR) of unmodified gold nanoparticles (AuNPs). The biosensing system consists of a broadband light source that covers the spectral range from 200 nm to 1700 nm, an optical attenuator, three types of 600 μm premium optical fibers with SMA905 connectors and a miniature spectrometer with a linear charge coupled device (CCD) array. The biosensing system with optical fibers is low-cost, simple and is well-proven for the detection of melamine. Its working principle is based on the color changes of AuNPs solution from wine-red to blue due to the inter-particle coupling effect that causes the shifts of wavelength and absorbance in LSPR band after the to-be-measured melamine samples were added. Under the optimized conditions, the detection response of the LSPR biosensing system was found to be linear in melamine detection in the concentration range from 0μM to 0.9 μM with a correlation coefficient (R2) 0.99 and a detection limit 33 nM. The experimental results obtained from the established LSPR biosensing system in the actual detection of melamine concentration in liquid milk samples show that this technique is highly specific and sensitive and would have a huge application prospects.

Development of nanofibrillated cellulose coated with gold nanoparticles for measurement of melamine by SERS

The objective of this study was to develop nanofibrillated cellulose (NFC)-based substrate for rapid detection of melamine in milk by surface-enhanced Raman spectroscopy (SERS). NFC were served as a highly porous platform to load with gold nanoparticles (AuNPs), which can be used as a flexible SERS substrate with nanoscale roughness to generate strong electromagnetic field in SERS measurement. The NFC/AuNP substrate was characterized by UV–Vis spectroscopy and electron microscopy. Milk samples contaminated by different concentrations of melamine were measured by SERS coupled with NFC/AuNP substrate. The spectral data analysis was conducted by multivariate statistical analysis [i.e. partial least squares (PLS)]. Satisfactory PLS result for quantification of melamine in milk was obtained (R = 0.9464). The detection limit for melamine extracted from liquid milk by SERS is 1 ppm, which meets the World Health Organization’s requirement of melamine in liquid milk. These results demonstrate that NFC/AuNP substrate has improved homogeneity and can be used in SERS analysis for food safety applications.

Computational design of molecularly imprinted polymer for direct detection of melamine in milk

ABSTRACTA novel protocol for use of molecularly imprinted polymer (MIP) in analysis of melamine is presented. Design of polymer for melamine has been achieved using a combination of computational techniques and laboratory trials, the former greatly reducing the duration of the latter. The compatibility and concerted effect of monomers and solvents were also investigated and discussed. Two novel open-source tools were presented which are the online polymer calculator from mipdatabase.com and the application of the Gromacs modelling suite to determine the ideal stoichiometric ratio between template and functional monomer. The MIP binding was characterised for several structural analogues at 1–100 μM concentrations. The use of divinylbenzene (DVB) as cross-linking polymer and itaconic acid as functional monomer allowed synthesis of MIP with imprint factor (IF) of 2.25 for melamine. This polymer was used in high-performance liquid chromatography (HPLC) for the rapid detection of melamine in spiked milk samples with an experimental run taking 7–8 min. This approach demonstrated the power of virtual tools in accelerated design of MIPs for practical applications.

Silver nanoparticles for melamine detection in milk based on transmitted light intensity

Melamine (C3H6N6) is a commercially synthesised organic compound which is illegally added to milk during processing to boost the apparent protein content. Melamine cannot be metabolised by the body and forms insoluble crystals which causes tissue damage and renal dysfunction. Hence, there is a need to develop a rapid and reliable method for melamine detection. Attempted here is to develop a simple procedure to detect melamine in milk using silver nanoparticles (AgNPs). Borohydride-reduced AgNPs, citrate-capped AgNPs and polyvinyl pyrrolidone-capped AgNPs are synthesised and characterised for their size, composition, structure etc. and studied for the suitability in this application. The first two NPs are determined to be suitable for this detection and exhibit a colour change from pale yellow to red at different concentration of melamine. To measure the melamine concentration, quantification of colour change and the transmitted light intensity is done using a colour sensor when the mixture is exposed to standard light source. Compared with visual observation in colour change, the transmitted light intensity provides more information to quantify melamine, more specifically citrate-capped AgNPs are found to provide better results than borohydride-reduced AgNPs. The results of this study are much agreeable to that obtained through standard laboratory experiment. Hence, this proposed method would be useful in developing an electronic-based melamine testing instrument that can be used rapidly at home.

A portable multi-channel sensing device using Au nano-urchins as probes for melamine detection in milk

Facile detection of melamine in milk was realized through a portable multi-channel sensing device using Au nanoparticles with urchin-like structures as sensing probes.

A highly selective melamine sensor relying on intensified electrochemiluminescence of the silica nanoparticles doped with [Ru(bpy)3]2+/molecularly imprinted polymer modified electrode

In this work, a novel and highly selective molecularly imprinted sensor for the detection of melamine in milk using electrochemiluminescence (ECL) is reported. The preparation was carried out by modification of a glassy carbon electrode with a composite of silica nanoparticles doped with [Ru(bpy)3]2+ (RUDS) and molecularly imprinted polymer (MIP). The keys of the sensor were to employ RUDS as an ECL luminophore to prevent [Ru(bpy)3]2+ leaching from the modified electrode and MIP as a material for selective recognition. Taking advantage of the MIP pre-concentration effect, melamine could be extracted from the solution and detected by the resulting ECL signal enhancement of [Ru(bpy)3]2+. Under optimized conditions, the relative ECL signal was proportional to the logarithm of melamine concentration in the range of 1×10−12–1×10−7molL−1, with a detection limit as low as 5×10−13molL−1. Compared with the RUDS/non-imprinted polymer, the RUDS/MIP modified electrode displayed high recognition ability, good reproducibility, and stability. To verify its reliability, the fabricated ECL sensor was used for determining the concentration of melamine in milk.

Determination of melamine in milk using surface plasma effect of aggregated Au@SiO2 nanoparticles by SERS technique

A simple and rapid method to detect melamine in liquid milk by Surface-enhanced Raman Scattering (SERS) technique was presented. The pretreatment procedure of milk samples only contains hydrochloric acid treatment and twice centrifugation. In order to reduce the distortion about the Raman signals originating from charge transfer and electronic tunnelling effect, SiO2 shell-isolated gold nanoparticles (Au@SiO2 NPs) instead of Au NPs were employed to enhance signal intensity. Aggregation occurs when the Au@SiO2 NPs colloid is mixed with the melamine solution or the treated milk containing melamine. Different from aggregated Au NPs, these aggregated Au@SiO2 NPs on Cu substrate can undistortedly enhance the Raman signals of melamine using surface plasma effect. Quantitative analysis was tried and the results showed a good linearity (R2 ≈ 0.99) when the melamine concentration was between 0.5 mgL−1 and 5 mgL−1. The detection sensitivity satisfies the requirement of the Codex Alimentarius Commission and this method can be practically used for melamine detection in milk.