One-step detection of melamine in milk by hollow gold chip based on surface-enhanced Raman scattering

Au nanoparticles decorated ZnO/ZnFe2O4 composite SERS-active substrate for melamine detection

Surface-enhanced Raman scattering (SERS) based on plasmonic metal nanoparticles and semiconductors has been used as performance-enhancing structures for sensing trace chemicals. We have selected a case of oxide functional oxide organic nanostructure between ZnFe₂O₄ and ZnO, denoted as ZZF. By decorating such nanostructure with AuNPs, to identify R6G in varying concentrations (10^-6 M - 10^-12 M), an enhancement factor of 1.6 × 10⁸ was observed. The material was used for the identification of melamine in the concentration range of 0.39 μM-7.92 μM. This high-performance nanocomposite provides improved melamine sensitivity towards SERS and the limit of detection as low as 0.39 μM. The Au-ZZF SERS substrate can yield a SERS enhancement factor of 1.37 × 10⁷. The experimental performance demonstrates that excellent SERS enhancement is due to electrons movement within ZZF and Au nanoparticles. Owing to its easy and effective synthesis methodology, this sensitive and specific SERS substrate is a promising technique to detect trace chemicals. We further study the best energetically favorable orientation of melamine molecules over the substrate leading to the SERS activity using density functional theoretical study.

Surface Enhanced Raman Spectroscopy: Applications in Agriculture and Food Safety

Recent global warming has resulted in shifting of weather patterns and led to intensification of natural disasters and upsurges in pests and diseases. As a result, global food systems are under pressure and need adjustments to meet the change—often by pesticides. Unfortunately, such agrochemicals are harmful for humans and the environment, and consequently need to be monitored. Traditional detection methods currently used are time consuming in terms of sample preparation, are high cost, and devices are typically not portable. Recently, Surface Enhanced Raman Scattering (SERS) has emerged as an attractive candidate for rapid, high sensitivity and high selectivity detection of contaminants relevant to the food industry and environmental monitoring. In this review, the principles of SERS as well as recent SERS substrate fabrication methods are first discussed. Following this, their development and applications for agrifood safety is reviewed, with focus on detection of dye molecules, melamine in food products, and the detection of different classes of pesticides such as organophosphate and neonicotinoids.

Plasmonic alloy nanochains assembled via dielectrophoresis for ultrasensitive SERS

It is great challenge and interesting for researchers to fabricate substrates for enhanced Raman and sensor, and assemble some easy-to-synthesize metallic nanomaterials into controllable nanostructures with special morphologies and arrangements, via alternating current (AC) electric field. The Au-Ag alloy nanoparticles (Au-Ag alloy NPs) colloidal suspension with excellent dispersibility synthesized by wet chemical method, and the morphology of the assembly can be well controlled by regulating the frequency of the AC electric field. Au-Ag alloy nanochains array (Au-Ag ANCs) with dense plasmonic "hot spots" is formed when the AC electric field of 4V_pp-30kHz is applied, which is supported by the result of finite element method (FEM) numerical simulation. Experimental results demonstrate that Au-Ag ANCs show excellent SERS activity: Au-Ag ANCs can detect both Rhodamine 6G (Rh6G) and crystal violet (CV) in the magnitude order of 10^-10 M, and the Raman peaks intensity and analyte concentration has a strong linear correlation (R² is 0.99339 and 0.95916, respectively). Besides, the introduction of Au-Ag ANCs makes the Raman spectra intensity of thiram (a pesticide) with a concentration of 30 ppm on the surface of the blank ITO glass significantly enhanced, and it can detect thiram with a concentration as low as 0.03 ppm. In addition, Au-Ag ANCs substrate exhibits great uniformity and stability, so they have considerable application potential in the field of quantitative detection of trace substances.

In situ and rapid determination of acetamiprid residue on cabbage leaf using surface-enhanced Raman scattering

BACKGROUND

Pesticide residues in agricultural products and foods pose a serious threat to human health, and therefore a simple, rapid and direct method is urgently needed for pesticide residue detection. In addition to realizing the detection of acetamiprid in cabbage extract solution, the main target of this study was to establish an in situ surface-enhanced Raman scattering (SERS) method, which could directly detect acetamiprid residue on cabbage leaf without the need for extraction. Acetamiprid was first used to contaminate the surface of fresh cabbage leaf, and then bimetallic silver-coated gold nanoparticles (Au@AgNPs) were added on the contaminated spots and dried for SERS measurement.

RESULTS

Results suggested that acetamiprid can be detected in cabbage extract and on cabbage leaf surface in situ using the SERS method based on the Au@AgNPs substrate. The limit of detection was 0.08 μg mL^-1 in cabbage extract and 0.14 mg kg^-1 on cabbage leaf, the recovery ranged from 80.5% to 105.5% and the relative standard deviation was in the range 4.37-10.63%.

CONCLUSIONS

The proposed SERS method provides an in situ, nondestructive and rapid way to detect acetamiprid residue on the surface of fruits and vegetables, which could serve as an auxiliary approach for early screening of contaminated produce in field or on site in the future. © 2020 Society of Chemical Industry.

Electrodeposition immobilized molybdenum disulfide quantum dots and their electrochemiluminescence application in the detection of melamine residues in milk powder

In this paper, one-step hydrothermal and electrodeposition methods were used to prepare a MoS2 quantum dot (QD) solid-phase electrochemiluminescent (ECL) electrode for the detection of melamine residues in milk powder. With the assistance of chitosan, MoS2 QDs fixed by the one-step electrodeposition method show better ECL performance than those by traditional deposition methods due to better dispersibility and stability. Based on the quenching of the MoS2 QDs ECL signal by melamine, quantitative detection of melamine in the sample was performed. The structure and morphology of a MoS2-CHIT/indium tin oxide (ITO) solid-phase ECL electrode were characterized by TEM and XPS, and melamine was detected by the ECL method using a three-electrode system. The proposed sensor exhibited good linearity in the range of 1.00 × 10-11 to 1.00 × 10-7 mol L-1 (ΔI = 12 100.62 + 1009.93 lg c (mol L-1), R2 = 0.997), and the method shows the advantages of simplicity and sensitivity compared to traditional detection methods. The interference of common ions in milk powder on the modified electrode was within 5%, and the recovery rate of real sample detection was within 97-98%. As a result, the proposed method is suitable for detecting melamine residues in milk powder.

Recent developments on gold nanostructures for surface enhanced Raman spectroscopy: Particle shape, substrates and analytical applications. A review

Surface enhanced Raman spectroscopy (SERS) is a powerful technique for sensitive analysis which is attracting great attention in the last decades. In this review, different gold nanostructures that have been exploited for SERS analysis are described, ranging from gold nanospheres to anisotropic and complex-shaped gold nanostructures, in which the presence of high aspect ratio features leads to an increment of the electromagnetic field at the surface of the nanomaterial, resulting in enhanced SERS response. In addition to the shape of the nanostructure, the interparticle nanogaps play a prominent role in the SERS efficiency. In this sense, different approaches such as nanoaggregation and formation of assemblies and ordered structures lead to the creation of the so-called hot spots. SERS measurements may be performed in solution, while usually the nanostructures are deposited building a SERS substrate, which can be created via attachment of chemically prepared gold nanostructures, as well as via top-down physical methods. Among the classical supports for creating the SERS substrates, in the last years there is a trend towards the development of flexible supports based on polymers as well as paper. Finally, some recent applications of gold nanostructures-based SERS substrates within the analytical field are discussed to spotlight the potential of this technique in real-world analytical scenarios.

Prevention of melamine-induced hepatorenal impairment by an ethanolic extract of Moringa oleifera: Changes in KIM-1, TIMP-1, oxidative stress, apoptosis, and inflammation-related genes

BACKGROUND/AIMS

Melamine (ML) is a common food adulterant and contaminant. Moringa oleifera is a well-known medicinal plant with many beneficial biological properties. This study investigated the possible prophylactic and therapeutic activity of an ethanolic extract of M. oleifera (MEE) against ML-induced hepatorenal damage.

METHOD

Fifty male Sprague Dawley rats were orally administered distilled water, MEE (800 mg/kg bw), ML (700 mg/kg bw), MEE/ML (prophylactically) or MEE+ML (therapeutically). Hepatic aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphate (ALP) in serum were measured. Serum total bilirubin, direct bilirubin, indirect bilirubin, protein, albumin, and globulin contents were also assayed, and urea and creatinine levels were determined. Moreover, antioxidant enzyme activity of glutathione peroxidase (GPx) and catalase (CAT) in serum levels were quantified. Complementary histological and histochemical evaluation of renal and hepatic tissues was conducted, and expression of oxidative stress (GPx and CAT) and apoptosis-related genes, p53 and Bcl-2, in hepatic tissue were assessed. In parallel, transcriptional expression of inflammation and renal injury-related genes, including kidney injury molecule 1 (KIM-1), metallopeptidase inhibitor 1 (TIMP1), and tumor necrosis factor alpha (TNF-α) in the kidney tissue were determined.

RESULTS

ML caused significant increases in serum levels of ALT, AST, ALP, total bilirubin, direct bilirubin, indirect bilirubin, urea, and creatinine. Further, ML treated rats showed significant reductions in serum levels of protein, albumin, globulin, GPx, and CAT. Distinct histopathological damage and disturbances in glycogen and DNA content in hepatic and renal tissues of ML treated rats were observed. KIM-1, TIMP-1, and TNF-α gene expression was significantly upregulated in kidney tissue. Also, GPx, CAT, and Bcl-2 genes were significantly downregulated, and p53 was significantly upregulated in liver tissue after ML treatment. MEE significantly counteracted the ML-induced hepatorenal damage primarily for co-exposed rats.

CONCLUSION

MEE could be an effective therapeutic supplement for treatment of ML-induced hepato-renal damage, probably via modulating oxidative stress, apoptosis, and inflammation.

Does melamine exposure during infancy cause rhabdomyolysis?

We investigated the possible toxic effects of melamine on muscle tissue in rats using biochemical, hematological and histopathological methods. We used three groups of female albino Wistar rats. The first group was given 0.1 ml saline. The second and third groups were given 50 and 75 mg/kg melamine dissolved in 0.1 ml saline, respectively, daily for 21 days. On day 45, all rats were sacrificed, and whole blood and plasma were analyzed for hematologic and biochemical characteristics. Muscle samples were stained with hematoxylin and eosin for histopathological investigation. Other sections were immunostained for matrix metalloproteinase-9 (MMP-9) and type IV collagen. We found a significant increase in the lymphocytosis-compliant leukocyte number in the 75 mg/kg melamine group compared to the other groups. We also found significant decreases in the hemoglobin levels and hematocrit values in the 75 mg/kg compared to the other groups. We found that the 75 mg/kg melamine group exhibited a significant increase in plasma aspartate aminotransferase (AST) activity compared to the other groups. Changes in plasma creatine kinase and lactate dehydrogenase activity were not statistically significant. Plasma AST activity and mean corpuscular hemoglobin levels were correlated with the lymphocyte:neutrophil ratio. We found mononuclear cell infiltration at the periphery of muscle bundles and in the connective tissue bundles in the melamine treated group. We found MMP-9 expression in muscle cell membranes and type IV collagen expression in degenerative connective tissue fibers. Whole blood, plasma and muscle tissue analysis indicated that the 75 mg/kg melamine group exhibited rhabdomyolysis that was associated with lymphocytosis and anemia. The underlying mechanisms by which melamine causes rhabdomyolytic effects remain unclear.

Review on Nanomaterial-Based Melamine Detection

Illegal adulteration of milk products by melamine and its analogs has become a threat to the world. In 2008, the misuse of melamine with infant formula caused serious effects on babies of China. Thereafter, the government of China and the US Food and Drug Administration (FDA) limited the use of melamine of 1 mg/kg for infant formula and 2.5 mg/kg for other dairy products. Similarly, the World Health Organization (WHO) has also limited the daily intake of melamine of 0.2 mg/kg body weight per day. Many sensory schemes have been proposed by the scientists for carrying out screening on melamine poisoning. Among them, nanomaterial-based sensing techniques are very promising in terms of real-time applicability. These materials uncover and quantify the melamine by means of diverse mechanisms, such as fluorescence resonance energy transfer (FRET), aggregation, inner filter effect, surface-enhanced Raman scattering (SERS), and self-assembly, etc. Nanomaterials used for the melamine determination include carbon dots, quantum dots, nanocomposites, nanocrystals, nanoclusters, nanoparticles, nanorods, nanowires, and nanotubes. In this review, we summarize and comment on the melamine sensing abilities of these nanomaterials for their suitability and future research directions.

Palliative effects of Moringa olifera ethanolic extract on hemato-immunologic impacts of melamine in rats

Melamine (MEL) is a widespread food contaminant and adulterant. Moringa olifera is a widely known medicinal plant with various pharmacological properties. Herein, this study aimed to investigate, for the first time, the probable protective or therapeutic role of M. olifera ethanolic extract (MOE) against MEL induced hemato-immune toxic hazards. Fifty Sprague Dawely male rats were orally treated with distilled water, MOE (800 mg/kg bw), MEL (700 mg/kg bw), MOE/MEl or MOE + MEl. Erythrogram and leukogram profiling were evaluated to assess hematological status. Innate immune functions were evaluated via measuring lysozyme levels, nitric oxide concentration, and bactericidal activity of phagocytes. Serum immunoglobulin levels were estimated as indicators of humoral immunity. Histologic and immunohistochemical evaluations of splenic tissues were also performed. The results indicated that MEL caused a significant decline in RBC, Hb, PCV, total WBC, neutrophil, lymphocyte, phagocytes bactericidal activity, lysozyme activity, nitric oxide, total IgM and IgG levels. Also, MEL induced various pathologic lesions in the spleen with strong expression of CD4 and CD8 positive cells. MOE significantly counteracted the former anaemic, leucopenic, innate and humoral depressant effects of MEL particularly at co-exposure. In conclusion, these findings revealed that MOE could be candidate therapy against MEL hemato-immunotoxic impacts.

Integrated preservation and sample clean up procedures for studying water ingestion by recreational swimmers via urinary biomarker determination

The use of cyanuric acid as a biomarker for ingestion of swimming pool water may lead to quantitative knowledge of the volume of water ingested during swimming, contributing to a better understanding of disease resulting from ingestion of environmental contaminants. When swimming pool water containing chlorinated cyanurates is inadvertently ingested, cyanuric acid is excreted quantitatively within 24 h as a urinary biomarker of ingestion. Because the volume of water ingested can be quantitatively estimated by calculation from the concentration of cyanuric acid in 24 h urine samples, a procedure for preservation, cleanup, and analysis of cyanuric acid was developed to meet the logistical demands of large scale studies. From a practical stand point, urine collected from swimmers cannot be analyzed immediately, given requirements of sample collection, shipping, handling, etc. Thus, to maintain quality control to allow confidence in the results, it is necessary to preserve the samples in a manner that ensures as quantitative analysis as possible. The preservation and clean-up of cyanuric acid in urine is complicated because typical approaches often are incompatible with the keto-enol tautomerization of cyanuric acid, interfering with cyanuric acid sample preparation, chromatography, and detection. Therefore, this paper presents a novel integration of sample preservation, clean-up, chromatography, and detection to determine cyanuric acid in 24 h urine samples. Fortification of urine with cyanuric acid (0.3-3.0 mg/L) demonstrated accuracy (86-93% recovery) and high reproducibility (RSD < 7%). Holding time studies in unpreserved urine suggested sufficient cyanuric acid stability for sample collection procedures, while longer holding times suggested instability of the unpreserved urine. Preserved urine exhibited a loss of around 0.5% after 22 days at refrigerated storage conditions of 4 °C.

Detection of melamine adulteration in milk by near-infrared spectroscopy and one-class partial least squares

Melamine is a noxious nitrogen-rich substance and has been illegally adulterated in milk to boost the protein content. The present work investigated the feasibility of using near-infrared (NIR) spectrum and one-class partial least squares (OCPLS) for detecting the adulteration of melamine. A total of 102 liquor milks were prepared for experiment. A special variable importance (VI) index was defined to select 40 most significant variables. Thirty-two pure milk samples constitute the training set for constructing a one-class model and the other samples were used for the test set. The results showed that on the independent test set, it can achieve an acceptable performance, i.e., the total accuracy of 89%, the sensitivity of 90%, and the specificity of 88%. It seems that the combination of NIR spectroscopy and OCPLS classifier can serve as a potential tool for rapid and on-site screening melamine in milk samples.

Graphene laminated gold bipyramids as sensitive detection platforms for antibiotic molecules

Atomic layers of graphene were optomechanically laminated onto gold bipyramids (length of ∼95 ± 3 nm and sharp tip radius less than 10 nm) using laser induced shock pressure. The fabricated graphene-gold bipyramid hybrids were employed as surface enhanced Raman scattering (SERS)-active substrates for the detection of tetracycline, an antibiotic, at very low concentrations.

A three-dimensional silver nanoparticles decorated plasmonic paper strip for SERS detection of low-abundance molecules

The fabrication of SERS substrates, which can offer the advantages of strong Raman signal enhancement with good reproducibility and low cost, is still a challenge for practical applications. In this work, a simple three-dimensional (3D) paper-based SERS substrate, which contains plasmonic silver-nanoparticles (AgNPs), has been developed by the silver mirror reaction. This paper strip was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), etc. Pretreatment of the paper as well as the reaction time, temperature, and reagent concentrations for the silver mirror reaction were varied for further studies. With the optimized experimental parameters, the AgNPs synthesized and distributed in-situ on the paper strip could give more favorable SERS performance. The limit of detection (LOD) as low as 10(-11)M for Rhodamine 6G (R6G) and 10(-9)M for p-aminothiophenol (p-ATP) plus wide linear range for the log-log plot of Raman intensity versus analyte concentration were achieved. The detection of R6G in rain water was also carried out successfully. The merits of this protocol include low cost, easy operation, high sensitivity and acceptable stability, which make it ideal for the detection of environmental samples in trace amounts.

Rapid monitoring of benzylpenicillin sodium using Raman and surface enhanced Raman spectroscopy

At present, fluorescence spectroscopy, ultraviolet spectroscopy and infrared spectroscopy are usually used to detect drug molecules, however the information about using Raman spectroscopy to detect drug molecules is very few. In this work normal Raman spectroscopy and surface-enhanced Raman spectroscopy were utilized to study benzylpenicillin sodium (NaBP). The results show that NaBP is close to the surface of silver substrate through the carboxyl group, and the detection limit of NaBP is reduced to 1×10(-7) mol/L. Accordingly, the quantitative analysis of NaBP can be carried out in the range of 1×10(-4)-1×10(-7) mol/L concentration. And it is proved that NaBP is not stable in acid and alkali conditions and the decomposition reaction is very complex.

SERS investigation of ciprofloxacin drug molecules on TiO2 nanoparticles

TiO₂ nanoparticles with different crystallinity were synthesized and served as SERS-active substrates for SERS detection of ciprofloxacin (CIP) drug molecules.