Melamine Concentration Research Articles

ImageJ and smartphone app chemistry analyzer using image-based colorimetric assay for quantitative detection of melamine

Abstract A smartphone-assisted microchemistry analyzer with an image-based colorimetric assay using ImageJ and a smartphone app detection method was successfully developed for the quantitative detection of melamine (MEL). The color changes of the MEL in the colloidal gold lateral flow immunoassay strip were captured and analyzed using a smartphone-controlled analyzer with an LED light source and a smartphone camera. The smartphone camera and light source were used to read the colorimetric signal from the strip, and a smartphone app was written and installed onto the smartphone. The quantitative analysis was validated with ImageJ and smartphone app colorimetric analysis. The limits of detection (LODs) for ImageJ and the smartphone app were calculated as 0.30 and 0.07 mg/L, respectively. The highly quantitative relationships between the MEL concentrations and the optical density and gray value of the ImageJ and smartphone app detection method. The designed image-based biosensor is successfully applied to detect MEL in solution of standard MEL and commercial milk samples.

Rapid identification of milk powder adulteration based on surface-enhanced Raman spectroscopy

In recent years, milk powder adulteration has emerged as a matter of great concern. In this study, a rapid, accurate, and efficient detection method based on surface-enhanced Raman spectroscopy (SERS) combined with principal component analysis (PCA) was established to detect milk powder adulteration. The “coffee ring” effect-based gold nanoparticles (Au NPs) as the SERS-enhancing substrate were coupled with a portable Raman spectrometer, which enabled the differentiation of various brands of milk powder and the detection of melamine in milk powder. The substrate exhibited good SERS enhancement ability with an enhancement factor of 104. Furthermore, a strong linear correlation with a correlation coefficient (R2) of 0.9903 was observed between the melamine Raman intensity and concentration from 0.5 to 5.0 mg/kg. The calculated limit of detection of melamine (LOD) was 0.15 mg/kg, while the limit of quantitation (LOQ) was 0.5 mg/kg. In addition, when the method was applied to the detection of melamine in milk powder samples, this method achieved the recovery rates of melamine in milk powder samples ranged from 92.83% to 98.86% with relative standard deviations between 0.84% and 1.14%. In summary, the established method offers the advantages of cost-effectiveness, less sample requirement, and shorter detection time, meeting the needs for milk powder classification and rapid melamine detection.

Unraveling the contribution of melamine tableware for human internal exposure to melamine and its derivatives: Insights from crossover and biomonitoring studies

Melamine tableware can release melamine in daily-use; however, currently there is insufficient evidence to support whether the amount released could pose human exposure risk. We therefore conducted two studies, one is 8-day randomized crossover trial involving 27 volunteers who used melamine and stainless-steel tableware in turn (n = 648) and the other is cross-sectional study including 113 college students and 200 residents (n = 313) to further provide population-based evidence. The crossover study results showed that using melamine tableware could promote urinary concentrations of melamine, cyanuric acid (CYA), and ammelide by 42.1 %, 66.9 %, and 36.2 %, respectively. In the biomonitoring survey, students who are more accessible to melamine tableware in the canteen had 1.47-fold higher median urinary concentrations of melamine-related compounds than that of common residents (393 vs 267 nmol/L, p < 0.01). Additionally, positive associations between exposure to melamine and an oxidative stress indicator, 8-oxo-7,8-dihydroguanine (β = 1.13, 95 % CI: 0.32, 1.94), and CYA and 8-hydroxy-2′-deoxyguanosine (β = 0.87, 95 % CI: 0.22, 1.53) were observed in students (p < 0.01), indicating long-term chronic exposure to these chemicals may induce molecular damage to nucleic acids. Our findings provide compelling evidence that frequent use of melamine tableware continues to be a potential threat to human health.

Биотестирование меламина с использованием многокомпонентной тест-системы

In recent decades, halogen-containing flame retardants have been gradually replaced by safer flame retardants, including nitrogen-containing compounds. However, their ecotoxicity is poorly studied. The ecotoxicity of melamine, a widely used nitrogen flame retardant, at concentrations equal to MPC in water (4 mg/L), 5 MPC (20 mg/L) and 10 MPC (40 mg/L) was assessed in this study using a complex of test organisms. The assessment of ecotoxicity using the dehydrogenase activity of Dietzia maris AM3 as a test microorganism revealed a stimulating effect of melamine at a concentration equivalent to the MPC; concentrations of 5 and 10 MPC inhibited the activity of dehydrogenases by 19.3% and 10.5%, respectively, indicating low toxicity. No toxic effects were observed on protococcal algae Chlorella vulgaris Beijer at any of the tested concentrations. The effect of melamine solutions on the mortality of crustaceans Daphnia magna Straus was noted only at a concentration of 10 MPC, and the mortality rate was 25%. Lemna growth inhibition test showed that melamine at concentrations equal to the MPC and 5 MPC had an inhibitory effect on the growth of Lemna minor L. It also caused a significant decrease (by 47–52%) in the total chlorophyll content in fronds when exposed to all studied concentrations of melamine.

Facile SERS screening of melamine in bovine milk with 2D printed AgNPs/glass fabric filter paper as the flexible substrate

Melamine is one of the most frequently detected adulterants in dairy products. The current study proposes a surface-enhanced Raman spectroscopy (SERS)-based analytical tool for fast and reliable screening of melamine in bovine milk. A hand-held Raman spectrometer was used in conjunction with a substrate composed of silver nanoparticles (AgNPs) that was 2D printed onto glass fiber (GF) filter paper. Under optimized conditions, a sensitive and fingerprint-like signal at 674 cm−1 was obtained. The AgNPs/GF substrate exhibited high sensitivity to melamine in milk down to 1.9498 × 10−5 mg/mL, which is well below the USA and EU safety limits (2.5 × 10−3 mg/mL). Remarkably, the proposed technology was also highly reproducible, showing spot-to-spot and block-to-block variations below 3.3 % and 4.9 % at 674 cm−1 in Raman intensity, respectively. The characteristic peak intensity and concentration of melamine showed an acceptable linear relationship (R2 = 0.9909) within the range of 0.0001–1 mg/mL. Overall, the method established in this study can provide an efficient and effective method for the quantitative target screening and detection of melamine in dairy products.

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

PurposeThe 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/approachA 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.FindingsAn 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/valueThe 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.

Environmental exposure to melamine and its derivatives and kidney outcomes in children

Melamine caused acute nephrotoxicity in a past food adulteration incident, but it is unclear whether and how widespread ambient exposure to melamine and related compounds might affect pediatric kidney health. We assessed cross-sectional associations between childhood exposure to melamine and its derivatives and biomarkers of kidney injury and health and explored potential heterogeneity by sex suggested by sex-dependent differences in renal physiology. We measured melamine and its derivatives ammeline, ammelide, and cyanuric acid (CYA) in spot urine samples collected from 192 children from an urban site (Seattle, WA) and 187 children from a rural site (Yakima, WA) aged 4–8 years in the Global Alliance to Prevent Prematurity and Stillbirth (GAPPS) Study. In addition, biomarkers of kidney injury were measured in the same urine samples, including albumin, total protein, KIM-1, NAG, NGAL, and EGF. We utilized linear regressions to examine associations between individual chemical exposures and kidney biomarkers. Interaction terms examined association modification by sex, as well as potential interactions between melamine and CYA. Despite comparable exposures, girls had higher levels of many kidney injury biomarkers compared to boys. A ten-fold higher melamine concentration was associated with a 18% (95% CI: 5.6%, 31%) higher EGF in the full sample, while ten-fold higher melamine was associated with a 76% (14.1%, 173%) higher KIM-1 in boys but not in girls (−10.1% (−40.6%, 36.1%), interaction p = 0.026). Melamine exhibited significant negative interactions with CYA in association with total protein and NAG that appeared to be specific to girls. Our results suggest possible associations between melamine exposure and markers of kidney injury that may be more pronounced in boys. These findings provide novel insights into melamine and related derivative compound health effects at low levels of exposure in children and emphasize the role of sex in mediating the relationship between nephrotoxicant exposure and kidney injury.

Dietary Risk Assessment of Cyromazine and Its Analogue Melamine in Evaporated and Infant Milk Samples in Nigeria

Background: The safety of milk is considered as a significant public health consideration and has been a key concern for consumers worldwide. The concentrations of cyromazine and its metabolic product, melamine, and their dietary risk assessment are investigated in this study.&#x0D; Methods: A total of 182 milk samples containing 15 brands were sampled between June and December 2022 from major and retail markets in Nigeria. After a solid-phase extraction procedure, the concentrations of the two compounds were determined using High-Performance Liquid Chromatography coupled with a Diode-Array Detector. Solid-phase extraction was utilized to extract local and imported evaporated and infant milk with CCl3COOH and CH3CN, followed by clean-up with NH4OH in MeOH. The extracts were analyzed with Agilent High-Performance Liquid Chromatography, including a Zorbax Eclipse+C18 column.&#x0D; Results: For both melamine and cyromazine, the Limits of Detection and Limits of Quantification were 1.29-1.48 and 3.94-4.50 µg/kg, respectively. The precision (Relative Standard Deviation&lt;1), recovery (99.5–102.5%), and regression (r2=0.989) were all excellent. Melamine concentration ranged between 57.6±18.9 and 930.3±379.9 µg/kg among the samples, and cyromazine was 57.2±12.3 and 670.9±87.8 µg/kg. Brand 2, imported from Holland, had the highest detection frequency for the two analytes. Disturbing levels of melamine were detected in Brand 2, particularly that 75 and 95% of the samples had melamine above the acceptable Maximum Residue Limit. However, the estimated daily exposure to the two additives was below the allowed daily intake values, and the Hazard Index (HI) in the different milk samples ranged from 0.02 to 1.22, with one sample having HI&gt;1.&#x0D; Conclusion: The exposure risk of melamine and cyromazine among the general population is acceptable, and smaller HI values demonstrated no significant potential risk for the Nigerian population according to the recommended guidelines. Regulatory agencies are encouraged to step up their surveillance activities to forestall the inclusion of prohibited additives in local and imported milk to protect public health.

Migration of Melamine and Its Derivatives from Melamine/Bamboo/Wheat Straw-Made Tableware Purchased from Internet Markets or Retail Shops in China.

The ecofriendly and sustainable concept of bamboo- and wheat straw-made tableware has gained attention in recent years. However, it is necessary to note that these kinds of tableware are composed of melamine (MEL)-formaldehyde resin with the addition of bamboo fibers or wheat straw. This study aims to explore the potential migration of MEL and its derivatives from the tableware and conduct a risk assessment. The study involved 46 bowls or cups purchased from Internet markets or retail shops in China, whose raw materials included MEL, bamboo, and wheat straw. There were four pieces of glass- or ceramic-made tableware used as the control group. Migration testing was performed according to the test conditions selected from the European Union Reference Laboratory for Food Contact Materials. Considering the realistic worst-case scenario, we measured the concentrations of MEL and its derivatives in food simulants using ultra-performance liquid chromatography-tandem mass spectrometry and estimated the exposure risks for adults and 1-year-old infants. MEL and its derivatives could migrate from MEL-, bamboo-, and wheat straw-made tableware with varying concentrations. The total migration was ranked as follows: bamboo-made tableware > MEL-made tableware > wheat straw-made tableware > glass- or ceramic-made tableware (p < 0.001). The primary contributor to the total concentration for MEL- and bamboo-made tableware was MEL, whereas cyanuric acid (CYA) was the main contributor for wheat straw-made tableware. Based on the total concentration of MEL and its derivatives and the strictest TDI value, the proportions of the calculated hazard quotient ≥1 for MEL-, bamboo-, and wheat straw-made tableware in adults were 53.50%, 92.30%, and 1.90%; and the proportions in 1-year-old infants increased to 86.00%, 100.00%, and 7.40%. The utilization of MEL-, bamboo-, and wheat straw-made tableware could be regarded as a significant source of human exposure to MEL and its derivatives. It is advisable for both adults and infants to refrain from using tableware manufactured with MEL and bamboo fiber, as it may increase the susceptibility to MEL-related diseases.

Trace level detection of melamine and cyanuric acid extracted from pet liquid food (milk) using a SERS Au nanogap substrate

This study reported an application of Au nanogap substrates for surface-enhanced Raman scattering (SERS) measurements to quantitatively analyze melamine and its derivative products at trace levels in pet liquid food (milk) combined with a waveband selection approach, namely variable importance in projection (VIP). Six different concentrations of melamine, cyanuric acid, and melamine combined with cyanuric acid were created, and SERS spectra were acquired from 550 to 1620cm−1. Detection was possible up to 200 pM for melamine-contaminated samples, and 400 pM concentration detection for other two groups. The VIP-PLSR models obtained correlation coefficient (R2) values of 0.997, 0.985, and 0.981, with root mean square error of prediction (RMSEP) values of 18.492 pM, 19.777 pM, and 15.124 pM for prediction datasets. Additionally, partial least square discriminant analysis (PLS-DA) was used to classify both pure and different concentrations of spiked samples. The results showed that the maximum classification accuracy for melamine was 100%, for cyanuric acid it was 96%, and for melamine coupled with cyanuric acid it was 95%. The results obtained clearly demonstrated that the Au nanogap substrate offers low-concentration, rapid, and efficient detection of hazardous additive chemicals in pet consuming liquid food.

Identification of melamine in milk using mid-infrared spectrometry

The paper presents a study of the infrared spectra of milk with melamine in the middle spectral range. The presence of absorption bands in the infrared spectra of a standard sample of melamine, milk without it and with its addition in different concentrations was analyzed in a comparative aspect. The presence of absorption bands of varying degrees of intensity in the infrared spectra has been established. It was revealed that the presence of melamine in milk can be identified by an absorption band in the region of 810 cm-1. The absence of this absorption band in the infrared spectra of milk with melamine concentrations of 0.1 and 0.5 mg/kg was determined. It was substantiated that the intensity of absorption bands in the infrared spectra depended on the concentration of melamine in milk. The use of spectrometry in the mid-infrared range to detect adulteration of milk has been proposed.

Optical detection of fat and adulterants concentration milk using TMDC (WS2 and MoS2)-surface plasmon resonance sensor via high sensitivity and detection accuracy

This paper introduces a surface plasmon resonance sensor for milk fat and melamine concentration detection, utilizing a transition-metal dichalcogenide (TMDC: WS2 and MoS2) based framework and incorporating an Ag–Pd bimetallic layer. The aim is to provide an innovative approach to monitor fat and melamine levels in milk. The palladium layer offers chemical stability and enhances sensitivity alongside the TMDC layer. Compared to the conventional SPR sensor, the maximum sensitivity, and detection limit are 409.36, 248.96°/RIU, and 0.0085, 0.0140 RIU, for detection of fat and melamine as sensing layer, respectively, related to the WS2 layer. The sensivity of sensor was expanded, due to the expanded field concentrated and profundity of infiltration of the sensor layer, coming about in a bigger interaction volume. The existence of the WS2 layer, with its notable imaginary component of the dielectric constant, enhances sensitivity while simultaneously enlarging the SPR curves. This study concludes that TMDC-Ag-Pd, offer a highly sensitive and efficient means of detecting fat cancentrion and melamine of milk. These findings suggest that TMDC-Ag-Pd optical sensor have great promise for application in the food industry.

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.

Twenty-four-hour temporal trend of melamine and its derivatives in urine in association with meal consumption: a panel study in Shanghai, China.

Timing of sampling is important for the exposure assessment of melamine (MEL) and its derivatives. This study aimed to investigate whether MEL and its derivatives in spot urine can effectively represent individual exposure levels throughout the day in adults and to explore their temporal trend before and after meal consumption for helping understand the timing of sampling and for assessing the potential exposure risk. This is a 2-day panel study with 43 college students being enrolled to provide urine specimens in 24 h (from the morning of the first day to the second day) and to answer a questionnaire on demographic characteristics, physical measurements, and time of having meal. Spearman correlation and Wilcoxon rank-sum test were used to examine the associations of the urinary concentrations of MEL and its derivatives in different sampled times and compare the concentrations' differences before and after meal consumption. Urinary concentrations of MEL and its derivatives (ammeline (AMN), ammelide (AMD), and cyanuric acid (CYA)) in the first-morning urine at the second day and randomly selected spot urine were positively associated with the average concentrations in the previous 24-h urine (all P ≤ 0.002). Urinary MEL concentration increased rapidly after meal consumption, reaching a maximum at approximately 3 h and then decreased gradually towards baseline (P = 0.006). Two subjects (4.65%) had a cumulative daily intake exceeding the severest tolerable daily intake. MEL and its three derivatives in spot urine can effectively represent the average concentrations in the previous 24-h urine in adults. Meal consumption is still a notable source of exposure to MEL for humans. These findings are important for choosing a better sampling strategy of performing exposure assessment. Meanwhile, the acute elevation in urinary MEL concentration following meal consumption may pose a potential health risk.

Optimization of physical vapor deposition process for low background nanoimprinted SERS substrate in quantitative melamine analysis

Uniformity, sensitivity, reproducibility, and cost are the critical parameters of practical surface-enhanced-Raman-spectroscopy (SERS) substrates. Herein, we proposed a High-Aspect-Ratio-Nano-Pillar-Array (HARNPA) substrate deposited silver by physical vapor deposition (PVD) methods (e.g. E-beam evaporation, sputtering, and a two-stage intermittent sputtering) to fabricate high-performance SERS substrates. The substrate by the E-beam evaporation has a significant SERS effect, but the Raman background induced by the exposure of the polymer HARNPA limits the analyte choice. The substrate by the sputtering method has better step coverage of silver but a lower enhancement factor. Therefore, we proposed a process of two-stage intermittent sputtering to solve these limitations. In addition, we define a factor called the signal-to-background peak ratio (S/B peak ratio) to evaluate the influence of the Raman background from the SERS substrate. Finally, we accomplished a SERS substrate with an S/B peak ratio of 3.48 by intermittent sputtering, which has the best linearity (R2 = 0.97) of the melamine concentration curve and the lowest detection limit (LoD = 5.6 × 10-7 M) that meets the regulatory requirements for melamine detection (3.96 × 10-6 M). The benefits of our SERS substrates are easy fabrication, high sensitivity (EF = 1.44 × 107), high reproducibility (CV = 8.4 %), and excellent uniformity (CV = 7 % in 4″ area), which are beneficial for mass production in the future.

Carbon dots derived from citric acid and urea as fluorometric probe for determining melamine contamination in infant formula sample

Melamine has been intentionally added into food products to increase the protein count at less cost, especially in dairy products for infant resulting in serious adverse effects on health of consumers. Therefore, this study aimed to develop a method to quantify melamine in dairy products based on the change of fluorescent properties of carbon dots (CDs) as sensing probe. CDs with green-fluorescent emission were synthesized from citric acid and urea under microwave irradiation. The synthesized CDs emitted fluorescence at the maximum wavelength of 538 nm with excitation wavelength of 410 nm. Thus, they provided high sensitivity and selectivity on melamine detection by which fluorescent emission of the CDs was increasingly quenched upon increasing melamine concentrations. Optimal conditions for melamine determination using the CDs was under pH 6, volume ratio between CDs and sample of 2:8 and reaction time of 15 min. The developed method provided high precision of melamine determination with less than 5% of %RSD (n = 5), wide detection range from 1.0 to 200.0 ppm, and high sensitivity with limit of detection (LOD) of 0.47 ppm and limit of quantification (LOQ) of 1.56 ppm, which is within the regulated level by the Food and Drug Administration of the United States for melamine in dairy products. Several analytical characterization techniques were conducted to elucidate the reaction mechanism between CDs and melamine, and the hydrogen bonding interaction was proposed.

Investigation of melamine and cyanuric acid concentration in several brands of liquid milk and its non-carcinogenic risk assessment in adults and infants.

In this study, the melamine and cyanuric acid concentration of widely used milk brands and the probability of non-carcinogenic risk of the brands for adults and infants were investigated. These values were 1.37mg/L, 1.10mg/L, and 1.09mg/L, which corresponded to creamy sterilized sample, high-fat (creamy) pasteurized sample, and low-fat (less-creamy) pasteurized sample, respectively. Similarly, the highest amount of cyanuric acid occurred in brand A with the values of 0.79 mg/L, 0.65 mg/L, and 0.64 mg/L, which was reported in the same samples mentioned for melamine. The HQ (Hazard Quotient) of melamine in the brands of A, B, C and D for adults was 0.0025, 0.0011, 0.0006 and 0.0008 respectively. These values for infants were reported as 2.2280, 0.9444, 0.5714 and 0.6714 respectively. The risk probability of melamine for adults was less than 1. However, the HQ in brand A for infants was greater than 1 (2.380), which indicate the high probability of non-carcinogenic risk. Furthermore, the HI (Hazard Index) values of the brands of A, B, C and D for infants were 2.7913, 1.1737, 0.7067 and 0.838, respectively. The simultaneous melamine and cyanuric acid in the brands A and B in for infants increase the non-carcinogenic risk probability by approximately 2.8 and 1.2 times, respectively. The results revealed that the melamine and cyanuric acid concentrations in creamy milk samples (0.5%) were higher than in less-creamy milk samples (2.5%). Moreover, the amount of the compounds in sterilized milk samples was higher than pasteurized. In this study, a conversion factor (0.7) was proposed in order to find out the concentration of cyanuric acid in milk sample with the amount of melamine is known but the cyanuric acid concentration is unknown.

Electrochemical sensor based on EDTA-functionalized polyorthophenylene diamine g-C3N4 nanocomposite for determination of melamine in milk

Melamine has little acute oral toxicity, but excessive consumption of melamine can be harmful to human health, and the development of a rapid and accurate detection method for melamine is very important. Since the electrochemical activity of melamine is very low, potassium ferrocyanide was used as a redox probe to help detect melamine using a modified carbon paste electrode. In this study, we present a novel, simple, sensitive, and low-cost electrochemical sensor for the rapid detection of melamine. The sensor was based on electrochemically synthesized polyorthophenylene diamine and graphitic-carbon nitride (g-C3N4) nanocomposite (g-C3N4/POPD), which was additionally functionalized by ethylenediaminetetraacetic acid (EDTA) in order to get structure (g-C3N4/POPD /EDTA) with advanced selectivity towards melamine. The synthesized g-C3N4/POPD/EDTA nanocomposite was characterized by FE-SEM, EDS, Mapping, ATR-IR, Raman, AFM, BET, and EIS techniques. Cyclic voltammetry and differential pulse voltammetry were used for the investigation of the electrochemical behavior of the modified electrode in the presence of melamine. The oxidation peak currents of ferrocyanide were linear with the concentration of melamine in the range from 0.01 µM to 0.1 µM with a linear coefficiency of 0.996. The detection limit was 9.0 nM. The sensor was successfully applied to the determination of melamine in milk products and showed high selectivity, sensitivity, and reproducibility.

An electrochemiluminescence sensor based on the CNTs and CdSe@ZnSe for determination of melamine in milk samples

In this work, a novel electrochemiluminescence (ECL) sensor based on the CdSe@ZnSe and CNTs was constructed for the detection of melamine. CdSe@ZnSe acted as the co-reaction promoter for the enhancement of Ru(bpy)32+/tri-n-propylamine (TPrA) system and CNTs acted as carriers to immobilize more CdSe@ZnSe. The initial ECL signal significantly amplified due to the synergistic effect of CNTs and CdSe@ZnSe. The ECL signal decreased with the addition of melamine, and the change value of ECL intensity (ΔI) was linearly related to the logarithm of melamine concentration. The constructed ECL sensor was able to detect melamine in the range of 1.0 × 10−11 − 1.0 × 10−7 M, and the detection limit was 3.3 × 10−12 M (S/N = 3). It can be used to detect melamine in milk samples.

Polyaniline-Coated Surface-Modified Ag/PANI Nanostructures for Antibacterial and Colorimetric Melamine Sensing in Milk Samples.

Silver nanoparticles (Ag NPs) are trusted candidates for many biological characteristics and applications due to their low toxicity and biologically benign nature. Due to inherited bactericidal characteristics, these Ag NPs are surface-modified with polyaniline (PANI), an organic polymer that has distinctive functional groups which have their role in inducing ligand properties. The Ag/PANI nanostructures were synthesized by the solution method, and their antibacterial and sensor properties were evaluated. Maximum inhibitory performance was seen with modified Ag NPs compared with their pure counterparts. The Ag/PANI nanostructures (0.1 μg) were incubated with E. coli bacteria, and almost complete inhibition was seen after 6 h. Furthermore, the colorimetric melamine detection assay by Ag/PANI as a biosensor also yielded efficient and reproducible results up to a 0.1 μM melamine concentration in daily-life milk samples. The chromogenic shift in color along with spectral validation through UV-vis spectroscopy and FTIR spectroscopy proves the credibility of this sensing method. Thus, high reproducibility and efficiency make these Ag/PANI nanostructures practical candidates for food engineering and biological properties.