Detection Of Melamine Research Articles

Development of Melamine Electrochemical Sensor Using Molecularly Imprinted Conducting Polyanilne-Oxalic Acid Blend as a Molecular Recognition Element

In the present work, oxalic acid doped molecularly imprinted conducting polyaniline film for melamine detection was prepared by in-situ-electrochemical polymerization on the glassy carbon electrode (GCE) using melamine as template. The optimal monomer/template molar ratio was attained to be 0.2:0.1:0.01 (aniline: oxalic acid: melamine) and molecular recognition properties towards melamine were evaluated by differential pulse voltammetry. Under optimal conditions the imprinted polymer film was used to detect different concentrations of melamine in standard solutions and real milk samples. Compared with the nonimprinted polymer (NIP), the molecularly imprinted polymer (MIP) film showed higher affinity and sensitivity towards melamine with a linear range, quantification limit and detection limit of 0.5-200 nM, 1.375 nM and 0.413 nM respectively. Furthermore, the polymer blend film showed good selectivity toward melamine, stability, reproducibility and practical applications for the determination of melamine in infant formula milk with the recovery of 92.32-102.49%. The doping of the polymer with oxalic acid enhanced the conductivity and sensitivity of the sensor.

AS1411-Templated Fluorescent Cu Nanomaterial’s Synthesis and Its Application to Detecting Melamine

Herein, we report a novel approach to AS1411-templated formation of fluorescent copper nanomaterials and their application to melamine detection. Fluorescent copper nanomaterials were formed at room temperature by using AS1411 as a template and ascorbic acid as reductant. However, the fluorescence intensity decreased obviously in the presence of melamine. Under the optimized conditions, the quenching fluorescence intensities of copper nanomaterials showed a good linear relationship with the concentration of melamine in the range of 50 μmol/L–120 μmol/L, and the correlation coefficient was 0.9823. In addition, the method was successfully applied in the detection of melamine in milk samples. This method was cost-effective and convenient without any labels or complicated operations. Thus, this work successfully develops the capping AS1411 scaffolds of copper nanomaterials detection of melamine.

Handheld fluorometer for in-situ melamine detection via interference synthesis of dsDNA-templated copper nanoparticles.

Fluorescent copper nanoparticles templated by dsDNA have gained significant research interest as they are inexpensive and easy to synthesize, and have found applications in the detection of a wide range of analytes. The presence of the analyte in the reaction mixture interferes with the synthesis of the copper nanoparticles and the subsequent drop in fluorescence can be correlated to the concentration of the analyte present in the solution. Analyte detection using copper nanoparticle-based assays is amenable for in-situ applications as the test does not require expensive reagents and can be performed at room temperature. However, expensive and sophisticated detection systems are required for the detection of copper nanoparticles due to the low fluorescence emission signal from these nanoparticles. This restricts the use of the technology to centralized labs. Utilizing a recently developed chemical technique for fluorescence enhancement, this paper presents the first report of a handheld fluorometer capable of detecting DNA-templated copper nanoparticles. The fluorometer is portable and constructed with low-cost, off-the-shelf components like a UV-LED and a PIN photodiode. The performance of the developed system is demonstrated through the detection of melamine in milk samples via the interference synthesis of copper nanoparticles. Melamine is an adulterant used in dairy products that is harmful to human health if present in levels above 1ppm. The developed system is capable of detecting up to 0.1ppm of melamine in milk samples with a linear relationship observed between the detector output and concentration of melamine in the range from 0.1ppm to 100ppm (R2=0.9979).

Detection of melamine and sucrose as adulterants in milk powder using near-infrared spectroscopy with DD-SIMCA as one-class classifier and MCR-ALS as a means to provide pure profiles of milk and of both adulterants with forensic evidence: A short communication

The present short communication reports a promising analytical method for authentication of milk based on first-order near-infrared (NIR) spectroscopic data coupled to data driven soft independent modeling of class analogy (DD-SIMCA). This one-class classifier was able to correctly classify all samples of genuine milk powder as members of the target class from samples of milk powder adulterated with melamine and sucrose in a concentration range of 0.8–2% (w/w) and 1–3% (w/w), respectively. Multivariate curve resolution − alternating least-squares (MCR-ALS) was applied as a complementary chemometric model to DD-SIMCA aimed at retrieving pure profiles, allowing to identify the chemical composition of samples properly attributed in the target class or not, providing further investigation from forensic point of view. In order to extend the prime focus of the present report, which was aimed at developing an appropriate chemometric model for authentication purposes, the quantification analysis was also performed. This was done by successful bilinear data decomposition of NIR spectra into pure profiles for the contributing components contained in the system studied (milk and adulterants), allowing to quantify analytes with strong overlapping profiles, even in the presence of an uncalibrated interferent, as demonstrated in this short communication using MCR-ALS under various constraints in order to decrease the rotational ambiguity.

Highly sensitive detection of melamine in milk samples based on N-methylmesoporphyrin IX/G-quadruplex structure

Melamine has a high nitrogen content thus is often illegally added to milk powder to phonily boost the protein percentage composition. Milk products containing melamine are harmful to babies and children. In the present work, a simple, label-free and turn-on fluorescence method to detect melamine with a high sensitivity and selectivity has been developed. The N-methylmesoporphyrin IX (NMM)/G-quadruplex structure is used as a signal reporter in this method to realize label-free detection of melamine. The detection limit of this method is 12.5 nM, which is much less than the maximum level permitted for infant formulas. The linear range is 0.05–1 μM (R2 = 0.98). The selectivity of this method is also very satisfactory. Furthermore, this method can be successfully applied for detection melamine in raw milk and milk powder.

Development of Molecularly Imprinted Conducting Polymer Composite Film-Based Electrochemical Sensor for Melamine Detection in Infant Formula.

Simple, fast, and sensitive molecularly imprinted composite thin-film-based electrochemical sensor developed by using in situ co-electropolymerization of aniline and acrylic acid in the presence of melamine as a template is described here. The prepolymerization complex formation was studied by using Fourier transform infrared (FTIR) spectrophotometry, while the film formation was performed and characterized by cyclic voltammetry, Fourier transform infrared (FTIR), and scanning electron microscopy (SEM). The optimization of important parameters and removal of melamine generated the binding sites in the polymer matrix, which can recognize melamine specifically. Electrochemical measurements were performed to achieve the linear range, the limit of quantification, and limit of detection of 0.1–180, 0.0573, and 0.0172 nM, respectively. The sensitivity of the sensor was attributed to the synergistic effects of amine from aniline and the carboxylic group from acrylic acid to form multiple noncovalent interactions with the template. Melamine-spiked infant formula and raw milk were analyzed by the developed sensor, and the recovery range of 95.87–105.63% with a relative standard deviation of 1.11–2.23% was obtained. The results showed that the developed sensor using the new composite polymer receptor is promising for the online monitoring of melamine in the food industries in the future.

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.

A High-matched Melamine Sensor Using Core/shell Nano Particles of Fe3O4@Polyrutin-COOH and Ionic Liquid as Imprinted Polymeric Monomers.

We describe here a magnetic molecular imprinted polymeric ionic liquid (MMIPIL) film by using a functionalized ionic liquid (3-vinyl-4-amino-5-imidazole carboxamide chloride, IL) and Fe3O4@Polyrutin-COOH as a functional monomer and supporting materials. The change in the direction of the charge density in the structure of MMIPIL polymer resulted in a red shift of about 100 nm for the characteristic group of -C=O. Polyrutin containing an electron-rich benzene ring and multiple hydroxyl groups not only prevented the aggregation of Fe3O4, but also benefitted to immobilize template molecules. More symmetric amino groups in the template molecules generated more hydrogen bonds and other synergistic effects between MEL and the functional monomers, which resulted in a highly-matched and highly stable MMIPIL sensor. The proposed magnetic sensor lowered the matching potential, and enhanced the signal for the detection of melamine (MEL) in milk powder. Under the optimum conditions, the MEL template molecule showed a significant linear relationship between 5.0 × 10-3 and 0.8 μg/L with a detection limit (S/N = 3) of 1.5 × 10-3 μg/L. The MMIPIL sensor showed wonderful selectivity and exhibited facile, fast and efficient results in the monitoring MEL with recoveries of between 96.5 and 108.3%.

Magnetic graphene oxide as sorbent for SPE of melamine from water

Melamine introduced into environment water through various industrial effluents can pose negative effects on ecosystem, thus it is required to establish suitable analytical methods for detection of melamine in environmental water samples. In this work, magnetic graphene oxide was synthesized and used as the sorbent for solid phase extraction (SPE) of melamine. The parameters that affect the extraction efficiency of melamine were studied. The optimum conditions, including sample pH, extraction and desorption time, and eluent volume were obtained. The analytical performance of the method was evaluated, and it was found that the limit of detection for melamine was 0.15μg/L and the relative standard deviation was 3.6 %. The proposed method was utilized in the detection of melamine in various water samples with recoveries of 92.0-95.8%.

Detection of copper nanoparticles templated by DNA using etched Fibre Bragg Grating sensor

In recent years, DNA-templated copper nanoparticles have been used to detect several important analytes, primarily through fluorescence spectrometry. However, the fluorescence of these nanoparticles decays within a few minutes making the quantitative estimation of analytes difficult. Despite the loss of fluorescence, the nanoparticles remain intact as evidenced by microscopy techniques like TEM and AFM. Here, etched fibre Bragg Grating (eFBG) sensors are presented as a detection/characterization tool for copper nanoparticles templated by double stranded DNA. The proposed sensor has a sensitivity of 1.5395 nm/RIU and a resolution of 0.00612 RIU. The formation of the copper nanoparticles on the DNA template attached to the eFBG sensor leads to a significant shift of ≈ 58 pm in the reflected Bragg wavelength signal. Further, the application of the proposed eFBG sensors for analyte detection utilizing the interruption in the synthesis of copper nanoparticles is demonstrated here with the example of melamine detection. The Bragg wavelength shift varies linearly with the log concentration of melamine ( ${R}^{2}=0.9482$ ) and the sensor can detect up to 0.1 ppm of melamine.

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.

Controllable and robust dual-emissive quantum dot nanohybrids as inner filter-based ratiometric probes for visualizable melamine detection.

The ratiometric fluorescence technique is of great interest due to its visualization characteristics. The construction of a reliable fluorescent ratiometric nanoprobe for high-sensitivity visual quantification is highly sought after but it is limited by poor stability and controllability. Herein, we report a robust dual-emissive quantum dot nanohybrid with precise color tunability and demonstrate its potential as a two-signal-change ratiometric probe for visual detection. A novel assembly strategy was developed for spatially implanting hydrophobic green and red quantum dots (QDs) into a silica scaffold to form a dual-emissive hierarchical fluorescent silica nanohybrid. The fluorescence intensity ratio and color of the nanohybrid were precisely tailored by altering the amounts of green and red QDs. Particularly, after the alkylsilane-mediated phase transfer and exterior silica shell growth, the nanohybrid exhibited the well-preserved fluorescence features of the original QDs and robust optical/colloid stability. An inner filter-based ratiometric nanoprobe for the visual determination of melamine was ultimately devised by combining the spectra-overlapped two-colored fluorescent nanohybrid with analyte-specific gold nanoparticles. Furthermore, based on the reversible fluorescence signal changes in two-colored QDs induced by melamine, a logic gate strategy for melamine monitoring was constructed. The newly developed fluorescent ratiometric nanoprobe shows great prospects for the visual and quantitative determination of analytes in a complex biological matrix.

Perovskite nanocrystals fluorescence nanosensor for ultrasensitive detection of trace melamine in dairy products by the manipulation of inner filter effect of gold nanoparticles

Barium sulfate-coated CsPbBr3 perovskite nanocrystals (CsPbBr3 NCs@BaSO4) was successfully synthesized that exhibited stable and intense fluorescence property in aqueous buffer. With the CsPbBr3 NCs@BaSO4 as signal readout, an ultrasensitive fluorescence nanosensor was developed for turn-on determination of melamine by the manipulation of inner filter effect of citrate-protected gold nanoparticles (AuNPs). The fluorescence of the CsPbBr3 NCs@BaSO4 was remarkably quenched by the AuNPs due to inner filter effect. This inner filter effect could be weakened by the addition of melamine as a result of melamine-triggering aggregation of the AuNPs and subsequently led to a recovery in the fluorescence of the CsPbBr3 NCs@BaSO4. The recovery ratio was proportional to the concentration of melamine in the range of 5.0–500.0 nmol/L. The limit of detection was 0.42 nmol/L and the relative standard deviation was 4.0% for the repetitive determination of 500.0 nmol/L melamine solution (n = 11). The nanosensor was successfully applied to analysis of melamine in dairy product samples.

One-pot biosynthesis of silver nanoparticle using Colocasia esculenta extract: Colorimetric detection of melamine in biological samples

Here we report an eco-friendly and robust silver nanoparticles (AgNPs) as a simple and sensitive probe for the detection of melamine in biological samples. The AgNPs were synthesized using the extract of Colocasia esculenta. The spherical shaped and monodispersed AgNPs were obtained with an average particle size of 20 nm. The as synthesized colorimetric probe was morphologically and spectroscopically characterized using transmission electron microscope and fourier-transform infrared and UV–vis spectrometry respectively. This method is based on the melamine induced aggregation of AgNPs, hence, color changes from yellow to orange red. Various experimental parameters such as effect of pH and time on the detection of melamine was investigated to enhance the sensitivity of the developed method. Under optimized conditions, the limit of detection and limit of quantification were found to be 0.070 ppm and 1.60 ppm respectively with a recovery values ranging from 95.0–103%. The findings of this study resulted in the development of highly sensitive and selective sensing probe for the detection of melamine in biological samples.

A ratiometric fluorescence probe for melamine detection based on luminescence resonance energy transfer between the NaYF4:Yb, Er upconversion nanoparticles and gold nanoparticles

In this paper, a novel ratiometric fluorescence probe for melamine detection based on luminescence resonance energy transfer (LRET) between the NaYF4:Yb, Er upconversion nanoparticles (UCNPs) and gold nanoparticles (AuNPs) was developed. The detection mechanism could be interpreted to the AuNPs quenched the fluorescence intensity (F542 and F654) of the UCNPs under 980 nm excitation. after melamine addition, the fluorescence intensity of the UCNPs was recovered due to the aggregation of Au NPs. A good linear relationship between the ratio of F542 to F654 nm (F542/F654) was obtained in ranges of 20-200 μg/L of the melamine concentration and the limit of detection was 8.8 nM. Besides, The probe exhibited an excellent selectivity and good sensitivity to melamine, and achieved the melamine detection in real sample. This work paved a new avenue for the potential practice application for commercial instantaneous determination of the melamine.

Electrochemical Detection of Melamine by Using Reduced Graphene Oxide-Copper Nanoflowers Modified Glassy Carbon Electrode.

In this work, a robust and reliable electrochemical sensor was developed for sensitive detection of non-electroactive melamine (MEL) using a modified glassy carbon electrode with ascorbic acid (AA) as the active recognition element. To increase the current signal of AA, the working electrode was successively modified with l-arginine (l-Arg) and reduced graphene oxide–copper nanoflower composite. The voltammetry measurements denoted that the hydrogen bonding was formed between AA and MEL. Using the optimum conditions, the proposed enhanced sensor can detect MEL concentrations ranging from 10 × 10–9 to 9.0 × 10–8 M with a detection limit of 5.0 × 10–9 M that is proportional to the decrease of AA in the anodic peak current. Finally, the proposed sensor was successfully applied for the determination of MEL in commercial infant milk samples and good recovery values were obtained.

Determination of melamine and melamine–Cu(II) complexes in milk using a DNA-Ag hydrocolloid as the sensor

Simple and sensitive methods are required for the detection of melamine since melamine is harmful to human health. To detect the content of melamine and metal–melamine species in milk products, a new luminescent DNA silver hydrocolloid (AgNC53) was synthesized using a modified C3A-rich aptamer as the template. The emission of AgNC53 at 617 nm is sensitive to both melamine–Cu(II) and melamine, while almost no response to the free Cu(II) ion was detected. Moreover, AgNC53 is used to detect precisely the content of melamine in milk with a detection limit as low as 2.7 × 10−8 M. Thus, the AgNC53-based fluorescence method is a “label-free” fluorescence technology that can be used for the determination of melamine or the melamine–Cu(II) complex in milk products.

A Single Step Fast Track Methodology for In-Situ Detection of Hazardous Melamine by Using Highly Sensitive Polyphenolics Modified Nanogold Probe.

A single step fast track method is proposed to determine melamine based on strong hydrogen bonding between exocyclic amine group in melamine moiety and hydroxyl group of tannic acid (TA); acting as reducing and functionalizing agent for synthesis of gold nanoparticles (Au NPs). The proposed strategy is facile and highly time saving; as the detection of melamine with labelfree gold nanoparticles was accomplished within five minutes. The colorimetric probe exhibits high detection limit of 8 nM for melamine determination in raw milk, which is very low as compared to other capping ligands employed for Au NPs such as borohydride, citrate and 3,5-dihydroxybenzoic acid. The results show a highly sensitive linear range (0.03-2.5 μM) between absorption ratio and concentration of melamine with a correlation coefficient of 0.991. Proposed methodology is proven effective for on-site screening without using costly instrumentation.

3D aluminum/silver hierarchical nanostructure with large areas of dense hot spots for surface-enhanced raman scattering.

Plasmonic nanomaterials possessing large-volume, high-density hot spots with high field enhancement are highly desirable for ultrasensitive surface-enhanced Raman scattering (SERS) sensing. However, many as-prepared plasmonic nanomaterials are limited in available dense hot spots and in sample size, which greatly hinder their wide applications in SERS devices. Here, we develop a two-step physical deposition protocol and successfully fabricate 3D hierarchical nanostructures with highly dense hot spots across a large scale (6×6 cm2 ). The nanopatterned aluminum film was first prepared by thermal evaporation process, which can provide 3Dquasi-periodic cloud-like nanostructure arrays suitable for noble metal deposition; then a large number of silver nanoparticles withcontrollable shape and size were decorated onto the alumina layer surfaces by laser molecular beam epitaxy, which can realize large-area accessible dense hot spots. The optimized 3D-structured SERS substrate exhibits high-quality detection performance with excellent reproducibility (13.1 and 17.1%), whose LOD of rhodamine 6G molecules was 10-9 M. Furthermore, the as-prepared 3D aluminum/silver SERS substrate was applied in detection of melamine with the concentration down to 10-7 M and direct detection of melamine in infant formula solution with the concentration as low 10mg/L. Such method to realize large-area hierarchical nanostructures can greatly simplify the fabrication procedure for 3D SERS platforms, and should be of technological significance in mass production of SERS-based sensors.