Detection Of Melamine In Milk Research Articles

Experimental evaluation of ZnO nanorods based eco – friendly sensor for melamine detection in milk

Purpose The purpose of this study is to develop a straightforward method for creating a non – toxic metal oxide sensor capable of detecting melamine in milk at ambient temperature. Design/methodology/approach A low temperature, straightforward solution-based approach, specifically the hydrothermal method was utilized to apply the active sensing layer onto the substrate. Subsequently, analysis of the cyclic voltammetry (CV) profile was conducted to detect the concentration of melamine and determine its sensitivity. Findings An experimental analysis was performed on a nontoxic metal oxide-based sensor fabricated for detecting melamine sensitivity using the CV profile. The sensor’s performance was evaluated under three different concentrations of melamine (0.1 mmol, 0.2 mmol and 0.3 mmol). The results demonstrated a satisfactory sensitivity of 0.0297 µAmM−1cm−2 with a response time of 2 s. Originality/value The primary innovation of this research lies in the creation of a nontoxic and environmentally friendly sensor. The synthesis method employed featured significantly lower temperatures compared to existing literatures. Furthermore, the sensor achieved enhanced sensitivity along with rapid response times.

An ultra-sensitive detection of Melamine in milk using Rare-earth doped Graphene Quantum Dots- Synthesis and Optical Spectroscopic approach

This work focuses on a rapid and sensitive spectroscopic approach for detecting melamine in food products based on rare-earth Terbium-doped Graphene Quantum Dots (Tb-GQDs) synthesized using microwave and simple chemical conjugation methods. Citric acid and diethylene triamine (DETA) are the precursors of synthesizing GQDs. Terbium, a rare earth element with exceptional fluorescence properties, is doped onto the surface of the GQD to obtain dual photoemission with a broad spectral window and to provide excellent photo-stable characteristics. The as-synthesized Tb-GQDs were characterized using various spectroscopic and microscopic techniques. The synthesized Tb-GQD were spherical with a size of around 6 nm, showing approximately a quantum yield of 52 %, concerning the Standard-Quinine sulfate quantum yield of 54 %. Further, Tb-doped GQDs act as a fluorescent probe, were used to detect and quantify the concentration of melamine (0––5 µM) used as an adulterant in milk and milk products and obtained a maximum detection limit of 0.31 µM. This work concludes that the reported dual emitting Tb-GQDs provide a sensitive and effective platform for detecting melamine in real-time samples, especially in milk, and show promising potential in food industries.

A highly reliable, integration-time and laser-power independent, self-referenced SERS sensor with an extended dynamic range for the detection of melamine in milk

An ultrasensitive nanosculptured thin film (nSTF) based self-referenced SERS sensing platform for the detection of melamine in milk samples is developed. The self-referenced SERS platform consists of a monolayer of 4-aminothiophenol (4-ATP), sandwiched between Ag nSTF and Ag nanoislands (NIs), deposited over a Si substrate. The SERS signal from the sandwiched 4-ATP monolayer acts as a self-referenced signal. The self-referenced platform offers the advantage of independence of Raman signal on the laser power, integration time of the detector of the spectrometer, or ambient conditions. The dynamic range of the sensor, mostly limited by the limits on laser power and integration time of spectrometer, can now be extended due to the independence of the sensor from these two parameters. A significant enhancement in the Raman signal of rhodamine 6G of the order of 1013 is achieved for the SERS active substrate. The self-referenced SERS sensor offers a linear response over the extended dynamic range from 0.001 to 10 ppm for melamine in spiked milk samples. The achieved limit of detection for melamine in spiked milk samples is 1 ppb. The self-referenced sensor will be of great value for real-time detection of melamine in milk samples, and food safety.

Highly sensitive Ag/PMMA SERS substrate with dense and uniform nano-forest structure for the detection of melamine in milk

In this paper, a large-area uniform nano-forest structure was produced on PMMA support by simple plasma treatment, and a highly sensitive Ag/PMMA SERS substrate was obtained by a thermal evaporation method. SEM images reveal the Ag/PMMA substrate featured densely distributed nano-trees containing lots of branches. FDTD simulation confirmed the gaps both on the top surface and in the body of the nano-forest were all effective hot spots, which could confine intense local electric field. By using crystal violet (CV) as the probe molecule, it was demonstrated the Ag-50/PMMA substrate prepared with a deposition time of 50 min could easily detect 10−10 M CV, and the enhancement factor (EF) was calculated to be 5 × 107. The Ag-50/PMMA substrate exhibited good uniformity and reproducibility with a relative standard deviation (RSD) of 3.6% and 7.8% respectively. Both the successful detection of melamine in milk with a concentration of 0.001 ppm, much lower than the permitted amount of melamine in milk, and the desirable accuracy exhibited in the recovery rate experiments demonstrated the satisfactory detection ability of the Ag-50/PMMA substrate in the real application. The high performance of the proposed SERS substrate ensured its great potential for applications in the field of food surveillance.

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.

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.

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.

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.

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.

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.

A signal-on fluorescent aptasensor by sensitized Tb3+ luminescence for detection of melamine in milk

A fluorescent aptasensor based on sensitized terbium(III) luminescence was constructed to detect melamine in milk. Tb3+ as the fluorescence probe can be sensitized by a guanine-rich single-stranded DNA sequence, so the complementary sequence of the polythymidine aptamer (cDNA) was modified with six consecutive guanine bases (G6). In the absence of melamine, melamine aptamer combined with cDNA to form a double helix structure, and G6 hybridized with the extended cytosine bases in the aptamer, resulting in low fluorescence intensity of Tb3+. In the presence of melamine, cDNA was released due to the specific recognition of melamine to the aptamer, resulting in stronger sensitized fluorescence intensity of Tb3+. Under the optimum conditions, the linear concentration of melamine in the milk ranged from 1.0 μg/mL to 10.0 μg/mL. This aptasensor can be used for the accurate and rapid detection of melamine in milk with a detection limit of 0.02 μg/mL, and has the advantages of high sensitivity, high efficiency, simple operation and low cost.

Visual and Optical Absorbance Detection of Melamine in Milk by Melamine-Induced Aggregation of Gold Nanoparticles.

The present study reported a facile method for the determination of melamine in milk powder products based on the aggregation of reactant-free 5 nm gold nanoparticles (AuNPs). The strong electrostatic attraction between the positively charged exocyclic amine groups present in the melamine molecule and the negatively charged ions bound to the AuNPs induced aggregation of the AuNPs, resulting in visible color changes that could be seen with the naked eye and monitored by ultraviolet–visible (UV–Vis) absorbance spectra. The method shows high sensitivity with detection limits of 1 × 10−9 M for visual detection and 1 × 10−11 M for UV–Vis analysis, which is far below the safety limit of melamine ingestion in infant formula (1 ppm = 7.9 × 10−6 M) and the detection limit acquired by most AuNP-based melamine detection methods. Good recoveries were obtained over the range of 94.7–95.5% with a relative standard deviation of mean recovery (RSD) ranging from 1.40 to 5.81. The method provides a simple, feasible, fast and real-time detection of melamine adulterants in infant formula by the naked eye, without the aid of advanced instruments.

Rapid and sensitive SERS detection of melamine in milk using Ag nanocube array substrate coupled with multivariate analysis

In this study, a facile Ag nanocube (NC) array substrate was fabricated for rapid SERS detection of melamine in milk. This easily-prepared substrate exhibited high Raman enhancement factor (~1.02 × 105) and good reproducibility with ~10.75% spot-to-spot variation in Raman intensity. Our proposed method can detect melamine as low as 0.01 ppm in standard solutions and 0.5 ppm in real milk samples after a simple one-step solvent extraction. Two multivariate analysis tools including partial least squares and support vector machines (SVM) were explored to develop reliable regression models for quantitative SERS analysis of melamine. By comparison, SVM regression models exhibited better predictive performance, especially in liquid milk, with root mean square error (RMSE) of calibration = 5.5783, coefficient of determination (R2) of calibration = 0.9807, RMSE of prediction = 1.9636, and R2 of prediction = 0.9736. Hence, this study offers a rapid and sensitive detection of adulterant melamine in milk samples.

SYBR Green I promotes melamine binding to poly-thymine DNA and FRET-based ratiometric sensing.

Melamine binding to polythymine (poly-T) DNA has been widely used to develop biosensors for the detection of melamine. In this work, SYBR Green I (SGI) was used to stain the binding reaction, and using DNA melting experiments, it was confirmed that poly-T DNA formed intramolecular binding complexes to bind multiple melamine molecules. In addition, while this system was insensitive to ionic strength, longer DNA and lower pH favored the binding of melamine. A fluorescence resonance energy transfer (FRET) sensor was designed by labeling a TAMRA and a Cy5 fluorophore on the two ends of T30 DNA, respectively. In the presence of SGI, FRET-based ratiometric detection was achieved with an apparent Kd of 85 μM and a limit of detection of 10.7 μM melamine. Without SGI, the sensitivity of detection was decreased by 47-fold. Interference from Hg2+ can be masked by adding EDTA. Detection of melamine in milk was achieved with recovery rates from 87.0 to 101.7%. This study has provided both basic biochemical insights and a ratiometric sensor for highly sensitive and robust detection of melamine.

Detection of Melamine in Milk Using Nanotechnology

Melamine is a poisonous substance which causes formation of kidney stone, nephrolithiasis, kidney injury in infant as well as in adult human beings by the ingestion of melamine contaminated food items, powder formula, powder milk. Nobel metal may be used to shape a type of nano-particles, known as NMNPs, which are inert (oxidation-resistant/corrosion resistant) and have special physical and optical properties. NMNPs are extremely detailed and responsive visual bio sensors for the analysis of a broad variety of inorganic and organic components and are particularly gold and silver nano-particles (AuNPs and AgNPs). Colorimetric changes result in a specific and sensitive identification of contaminants, heavy metals, nucleic acids, lipeid, protein, antibody, and other molecules through interactions between noble metal nanoparticles (NMNPs) and inorganic/organic molecules. Capping agents can react or transfer, causing cross-connection and non-cross binding, broadening, or modifying local surface plasmone resonance absorption, to the hydrogen bondage, electrostatic interaction, and steric effects of inorganic and organic molecules with surface NMNPs. A collection of independent, fast and low-cost diagnostic products with colorimetric or clear visual reading have been extensively applied to NMNPs-based bio sensors.

Aptamer-Facilitated Design of Gold Nanoparticle-Based Logic Gates for Cyromazine and Melamine Detection in Milk

In this paper, we developed a simply designed detection method for logic gates by using aptamers, cetyltrimethyl ammonium bromide, together with melamine and cyromazine to control the aggregation and dispersion of gold nanoparticles (AuNPs). First, either melamine or cyromazine can induce the aggregation of AuNPs, supporting an OR gate to detect whether they were present or not. Second, based on the fact that aptamer T31 can specifically bind with melamine, preventing the aggregation of AuNPs, an improved INHIBIT gate was also fabricated to find whether there was melamine. It has a detection limit of 0.12 ppm by the naked eye for the detection of melamine, and the limit of detection (LOD) by spectrophotometer is 2.2 ppb. Third, with the adsorption of aptamer Tcy1 on AuNPs and the strong coordination of Tcy1 with cyromazine, the addition of cyromazine and CTAB immediately resulted in the aggregation of AuNPs, giving rise to an AND gate. This gate has a detection limit of 0.17 ppm by the naked eye and the limit of detection (LOD) is 9.0 ppb by spectrophotometer. The system provided a good platform for the development of functional logic systems.

Ratiometric fluorescence detection of melamine in milk by a zirconium-based metal-organic frameworks composite

Melamine has biological toxicity and is forbidden to be used in food processing and food additives. The long-term ingestion of melamine will cause renal malfunction and metabolic problems of the urinary system, so it is of great significance for the rapid and selective detection of melamine. Herein, a zirconium-based metal–organic frameworks (Zr-based MOFs) encapsulated tris(2,2-bipyridyl)ruthenium (II) chloride hexahydrate ([Ru(bpy)3]2+) composite, donated as UiO-66-NH2@Ru, was reported and further studied its sensing performance for melamine based on ratiometric fluorescent method. The UiO-66-NH2@Ru was prepared from ZrCl4, 2-amino-terephthalic acid (TPA-NH2) and [Ru(bpy)3]2+ by one pot reaction through solvothermal method, which exhibited dual emission signals at 445 and 595 nm from single excitation of 350 nm. The corresponding two peaks showed different responses to melamine, that was, the obvious enhancement at 445 nm and the slow decrease at 595 nm, thus achieving the “on–off” ratiometric fluorescence detection. When the concentration of melamine was in the range of 0.27 to 110 μM, the ratio of fluorescence intensity F445/F595 had a good linear relation with the correlation coefficient R2 = 0.995 and the detection limit of 90 nM. The synthetic UiO-66-NH2@Ru probe implemented rapid determination of melamine in real sample of milk powder with high sensitivity and selectivity. Compared with the reported carbon dots, quantum dots, metal nanoclusters, nanocomposites and other fluorescent sensors, MOFs-based sensor have broadened the application of nanomaterials in melamine detection for the first time. This study also demonstrates the Zr-based MOFs as a platform to encapsulate fluorescent dye for constructing ratiometric sensor in the determination of melamine is feasible and exciting.

Synthesis of silver nanoparticles (AgNPs) using culinary banana peel extract for the detection of melamine in milk.

Melamine adulteration in milk is a serious health concern for the consumers. A reliable and sensitive technique using silver nanoparticle (AgNPs) was developed for the detection of melamine in milk sample. The AgNPs was synthesized using culinary banana peel extract (BPE) where pH, temperature, theamount of concentration of BPE and concentration of AgNO3 was standardized. The effect of the parameters used for the synthesis of AgNPs was analyzed by observing the colour of reaction mixture and surface plasmon resonance. The AgNPs synthesized under optimum conditions were characterized by SEM-EDX, TEM and FTIR. FTIR studies reveal the effective conjugation between AgNPs and bioactive components of BPE and formation of spherical and regular shaped AgNPs were confirmed by TEM images. Presence of Ag as a dominating metal in AgNPs confirmed the formation of AgNPs. The level of melamine above 0.5mg/L in milk could easily be detected through theinterference synthesis of AgNPs.

Nanostructured Cerium-Oxide-Based Screen Printed Electrode for Electrochemical Detection of Melamine via Ascorbic Acid

Nanostructured cerium oxide (CNP) was synthesized via co-precipitation and used as a base matrix to construct an enzyme-less electrochemical sensing platform for a non-electroactive analyte (i.e., melamine in the presence of ascorbic acid (AA)). CeO2 was screen printed (SP) on prefabricated gold electrodes for the indirect detection of melamine. The melamine concentrations varied in the range of 0.01 ppb to 10 ppm with a fixed amount of ascorbic acid (i.e., 50 ppm). Absorption spectra were obtained from 220 to 400 nm for all melamine concentrations. The cyclic voltammogram (CV) for different melamine concentrations was obtained in the applied voltage range of –1 to +1 V. The peak oxidation current reduced as a function of increased melamine concentration in the presence of ascorbic acid, which was supported by absorption studies. The obtained melamine sensitivities were 64.9 and 80.8 μA/ppb/mm2, respectively, without and with ascorbic acid. The limits of detection estimated from three times the signal-to-noise ratio were 1.5 × 10–3 and 2.4 × 10–3 ppb, which are the lowest values so far reported to the best of our knowledge. The electrochemical impedance study predicted the increase of the charge transfer characteristics in the presence of AA, which comprehensively correlated with the CV data. The developed sensor can be used for the detection of melamine in milk, dairy products, and other food items.

Quantitative SERS Assay on a Single Chip Enabled by Electrochemically Assisted Regeneration: A Method for Detection of Melamine in Milk.

Reusability of sensors is relevant when aiming to decrease variation between measurements, as well as cost and time of analysis. We present an electrochemically assisted surface-enhanced Raman spectroscopy (SERS) platform with the capability to reverse the analyte-surface interaction, without damaging the SERS substrate, allowing for efficient sensor reuse. The platform was used in combination with a sample pretreatment step, when detecting melamine from milk. We found that the electrochemically enhanced analyte-surface interaction results in significant improvement in detection sensitivity, with detection limits (0.01 ppm in PBS and 0.3 ppm in milk) below the maximum allowed levels in food samples. The reversibility of interaction enabled continuous measurement in aqueous solution and a complete quantitative assay on a single SERS substrate.