Detection of melamine in gluten, chicken feed, and processed foods using surface enhanced Raman spectroscopy and HPLC

Construction of three-face recognition molecularly imprinted polymers for extraction and detection of melamine via specific hydrogen bonding

Based on the principle that poly(thymine) ssDNA could recognize melamine (Mel) in aqueous media and the third face of Mel could be accessed by other hydrogen bonding molecules, UiO-66-NH2 was functionalized with poly(thymine) ssDNA and as the matrix to construct three-face recognition molecularly imprinted polymers (UDMIPs). The adsorption processes of UDMIPs towards Mel were accorded to Sips model and exhibited high adsorption capacity (QS=10.60 mg/g) and good imprinting factor (IF=2.67). UDMIPs could reach the adsorption equilibrium within 20 min. Competitive adsorption and regeneration experiments demonstrated that UDMIPs exhibited good selectivity and reusability. The adsorption machanism was investigated by CD spectroscopy. Combined with HPLC, UDMIPs were successfully employed to detect Mel in milk samples with recovery rates ranging from 88.4 % to 94.8 %.

A novel approach for identifying melamine adulteration in powdered milk with E-nose and AI

Dairy products are exceptionally nutritious and a key component of our diet. They are utilized in a wide range of food industries due to their significance. However, being highly popular and valuable, they are among the most common products subject to adulteration. Melamine is a chemical compound deliberately added to various food products. It is used to artificially increase the apparent protein content in milk, milk powder, pet food, and other foods. In this study, pure milk powder along with 12 different types of adulterated samples (with melamine content of 1, 2, 3, 4, and 5 ppm) in both dry and wet forms was analyzed using an electronic nose equipped with 8 metal oxide sensors to detect adulteration patterns. Principal Component Analysis (PCA), discriminant analysis (DA), and Support Vector Machine (SVM) methods were employed to analyze sensor response patterns and classification. Quantitative Descriptive Analysis (QDA) yielded a precision of 99.5 %, while Multi-Discriminant Analysis (MDA) achieved a precision of 98.5 %. Therefore, it appears that electronic nose technology with metal oxide sensors, along with chemometric methods, can be a truly effective tool for the rapid detection and classification of pure milk powder from adulterated materials.

Rapid and in-situ detection of iodine and potassium ferrocyanide in table salt using enhanced-Multipass cavity Raman scattering

The excess of iodine (I2) and potassium ferrocyanide (K4[Fe(CN)6]) to table salt are harmful to both human health and environment. To date, there are still a lack of suitable methods for simple, rapid and in-situ to detect the I2 and K4[Fe(CN)6] contents in table salt. Herein, we employ a highly sensitive Raman spectroscopy, which is based on multiple reflection cavities and multi-directional signal collection optical systems, to detect the concentration of trace ions in table salt. The detection limit of our technology is less than 1 mg/kg in salt solutions, signifying that the corresponding quantitative detection limit in table salt is 3.45 mg/kg. Simultaneously, the relative Raman intensity of the ion exhibits a highly linear correlation with concentration (R2 = 0.999), rendering it a molecular probe for I2 and K4[Fe(CN)6] within table salt. The accuracy of this molecular probe for I2, K4[Fe(CN)6], and sulfate (SO42-) content in different salts is 87.2 %, 89.6 % and 95.6 % respectively.Compared with the traditional method, this method has the advantages of low sample consumption (1g of salt), fast detection speed (10 min), and the measured sample can be saved.

Analysis of children's kidney stones and comparison to canine kidney stones: Both resulting from ingesting adulterated food products

Kidney stones resulting from ingestion of melamine-tainted food products were originally detected in dogs and cats in 2004 and 2007. Nephroliths were removed at necropsy from dogs that had died from acute kidney injury in Asia in 2004. Samples of these were submitted to our laboratories for analysis. The presence of a mixed s-triazine matrix comprising melamine, cyanuric acid, and ammelide, but no detectable ammeline was found in the canine stone samples we analyzed. The unusual and unique green coloration of these stones was attributed to the presence of biliverdin. The techniques developed in the canine study were applied to the analysis of human kidney stones. In 2008, high levels of melamine were detected in some infant formula and other liquid and powdered milk products originating from China. Human kidney stones, resulting from this type of contamination, were obtained from children, and analyzed using mass spectral techniques. The results indicated the presence of melamine, ammeline, uric acid, but no ammelide. No green color was observed, thereby eliminating biliverdin. Careful monitoring of food additives is warranted to prevent future problems in both animals and humans.

A semiconductor SERS sensor of corrosion-resistant PPy/GO composite film by electrochemical growth for detecting crystal violet residues in fresh fish tissue

Crystal violet (CV) residues in Marine food have produced a severe health threat in human life. In this study, we proposed a semiconductor surface-enhanced Raman scattering (SERS) sensor of corrosion-resistant Polyaniline/Graphene oxide (PPy/GO) film by electrochemical growth method to detect CV residues in fresh fish tissue. A PPy/GO dispersion solution was one-step deposited on a stainless steel sheet surface by electrochemical polymerization process to form a PPy/GO composite film acting as a semiconductor SERS substrate. Since the substrate of PPy/GO film was mainly composed of GO sheet without other metals, it had a good corrosion resistance. The SERS enhancement factor and charge transfer intensity PCT of PPy/Go SERS substrate for CV molecules were up to 1.18 × 106 and 0.903, respectively. Furthermore, the limit of detection (LOD) of PPy/GO SERS substrate could reach 1.58 nM. In addition, SERS sensor of PPy/GO film could identify CV residues in fresh fish tissues, and its recovery rate was 91.8 %-107 %. This preparing method and detecting method we proposed PPy/GO SERS substrate provide a new pathway for detecting CV residues in Marine food.

Three-dimensional nanoporous gold/gold nanoparticles substrate for surface-enhanced Raman scattering detection of illegal additives in food

Owing to their nanoscale size and porous structure, both colloidal gold nanoparticles (AuNPs) and nanoporous gold (NPG) have demonstrated good and stable surface-enhanced Raman scattering (SERS) activity, and are therefore widely used as SERS substrates for the rapid detection of various components in food, environmental, biological, and other samples. In this study, we fabricated a novel, sensitive, and reproducible composite three-dimensional (3D) substrate for rapid SERS-based detection of illegal additives in food products. AuNPs and NPGs were prepared by chemical reduction and chemical dealloying methods, with the particle size of AuNPs about 60 nm and the pore size of NPG in the range of 5-36 nm. The AuNPs were then assembled on the surface of NPG to form the composite substrate 3D-NPG/AuNPs, which was characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and other methods. Finally, the new SERS substrate combined with a portable Raman spectrometer was used to detect the illegal food additives 6-benzylaminopurine and melamine, with detection limits of 1 × 10-9 M and 5 × 10-7 M respectively. We further analyzed the relationship between the dealloying time-controlled morphology and the SERS properties of NPG, demonstrating that 3D-NPG/AuNPs as a novel SERS substrate have strong practical application potential in the rapid detection of food additives and other substances.

A review on nanomaterial-based SERS substrates for sustainable agriculture

The agricultural sector plays a pivotal role in driving the economy of many developing countries. Any dent in this economical structure may have a severe impact on a country's population. With rising climate change and increasing pollution, the agricultural sector is experiencing significant damage. Over time this cumulative damage will affect the integrity of food crops and create food security issues around the world. Therefore, an early warning system is needed to detect possible stress on food crops. Here we present a review of the recent developments in nanomaterial-based Surface Enhanced Raman Spectroscopy (SERS) substrates which could be utilized to monitor agricultural crop responses to natural and anthropogenic stress. Initially, our review delves into diverse and cost-effective strategies for fabricating SERS substrates, emphasizing their intelligent utilization across various agricultural scenarios. In the second phase of our review, we spotlight the specific application of SERS in addressing critical food security issues. By detecting nutrients, hormones, and effector molecules in plants, SERS provides valuable insights into plant health. Furthermore, our exploration extends to the detection of contaminants, chemicals, and foodborne pathogens within plants, showcasing the versatility of SERS in ensuring food safety. The cumulative knowledge derived from these discussions illustrates the transformative potential of SERS in bolstering the agricultural economy. By enhancing precision in nutrient management, monitoring plant health, and enabling rapid detection of harmful substances, SERS emerges as a pivotal tool in promoting sustainable and secure agricultural practices. Its integration into agricultural processes not only augments productivity but also establishes a robust defence against potential threats to crop yield and food quality. As SERS continues to evolve, its role in shaping the future of agriculture becomes increasingly pronounced, promising a paradigm shift in how we approach and address challenges in food production and safety.

Essential spectral pixels-based improvement of UMAP classifying hyperspectral imaging data to identify minor compounds in food matrix

Classifying big data in hyperspectral imaging (HSI) can be challenging when minor (low-concentrated) compounds are present in actual samples, as for chemical additives and adulterants in food matrix. Herein, we propose a new strategy to classify HSI data for the identification of adulterants in food material for the first time. This strategy is based on the selection of essential spectral pixels of full HSI data followed by the feature space construction using uniform manifold approximation and projection as well as the data clustering utilizing hierarchical clustering analysis on the reduced data (named ESPs-UMAP-HCA). We apply our approach to analyze two real NIR datasets and four new Raman datasets. Compared with non-ESPs UMAP-HCA and t-distributed stochastic neighbor embedding combined with ESPs and HCA (ESPs-t-SNE-HCA), the developed strategy provides well-separated clusters for major and minor compounds in food matrix. Finally, the adulterants as minor compounds are accurately identified, which is confirmed by the fact that the extracted spectra of them perfectly match with their pure spectra. In addition, their locations are found in the contribution map even though they are present in a few pixels. What's more, the proposed strategy does not need any a priori knowledge of the data structure and the class memberships and therefore reduced the studied difficulty and confirmation bias in the analysis of big HSI datasets. Overall, the proposed ESPs-UMAP-HCA method could be a potential approach for food adulteration detection.

Regulating the coordination capacity of ATMP using melamine: facile synthesis of cobalt phosphides as bifunctional electrocatalysts for the ORR and HER

Due to the complexity of the synthetic process of cobalt phosphides (CoP), ongoing efforts concentrate on simplifying the preparation process of CoP. In this work, amino tris(methylene phosphonic acid) (ATMP, L1) and melamine (MA, L2) are assembled into two-dimensional (2D) organic nanostructures by hydrogen bonding and ionic interactions via a supramolecular assembly, which greatly weakens the coordination ability of L1 with Co²⁺. As the introduced L2 is rich in carbon and nitrogen, it allows the cobalt-organophosphate complex to be placed under a strongly reducing atmosphere during the high-temperature calcination process to achieve an in situ phosphating purpose. The resulting catalyst (N-CoP/NC) exhibits the sought-after enhanced oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) performance. For the ORR in 0.1 M KOH, an enhanced onset potential (0.908 V vs. RHE) and diffusion limiting current (6.280 mA cm^-2) can be obtained, which is comparable to those of 20% Pt/C (0.911 V vs. RHE, 5.380 mA cm^-2). For the HER in 0.5 M H₂SO₄, an overpotential of 150 mV is required to drive a current of 10 mA cm^-2. Moreover, Density Functional Theory (DFT) calculations reveal the catalytic pathway of N-CoP/NC.

Quantum tunneling effect on the surface enhanced Raman process in molecular systems

In this paper, we theoretically study the effect of quantum tunneling on the surface enhanced Raman scattering (SERS) of a generic molecule confined in sub-nanometer nanocavities formed by metallic dimers. The tunneling effect was described by the quantum corrected model in combination with finite element simulations. The SERS spectra were calculated by a density matrix method. Simulation results demonstrate that both the field enhancement and the molecular SERS spectra are very sensitive to the size of the cavity. By decreasing the gap size, the local field enhancement first increases then starts to be significantly suppressed as a result of the tunneling effect which neutralizes the positive and negative induced charges in the nanocavity. Consequently, the SERS intensity also experienced dramatic decrease in the short gap distance region. We also show that both the plasmonic enhancement to the local field and the enhanced molecular decay rates have to be taken into account to understand the SERS properties of the molecule in such sub-nanometer nanocavities. These results could be helpful for the understanding of the surface enhanced spectral properties of molecular systems at sub-nanometer nanocavities.

Developing a Peak Extraction and Retention (PEER) Algorithm for Improving the Temporal Resolution of Raman Spectroscopy

In spectroscopic analysis, push-to-the-limit sensitivity is one of the important topics, particularly when facing the qualitative and quantitative analyses of the trace target. Normally, the effective recognition and extraction of weak signals are the first key steps, for which there has been considerable effort in developing various denoising algorithms for decades. Nevertheless, the lower the signal-to-noise ratio (SNR), the greater the deviation of the peak height and shape during the denoising process. Therefore, we propose a denoising algorithm along with peak extraction and retention (PEER). First, both the first and second derivatives of the Raman spectrum are used to determine Raman peaks with a high SNR whose peak information is kept away from the denoising process. Second, an optimized window smoothing algorithm is applied to the left part of the Raman spectrum, which is combined with the untreated Raman peaks to obtain the denoised Raman spectrum. The PEER algorithm is demonstrated with much better signal extraction and retention and successfully improves the temporal resolution of Raman imaging of a living cell by at least 1 order of magnitude higher than those by traditional algorithms.

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.

Novel Nondestructive Biosensors for the Food Industry

An increasing number of foodborne outbreaks, growing consumer desire for healthier products, and surging numbers of food allergy cases necessitate strict handling and screening of foods at every step of the food supply chain. Current standard procedures for detecting food toxins, contaminants, allergens, and pathogens require costly analytical devices, skilled technicians, and long sample preparation times. These challenges can be overcome with the use of biosensors because they provide accurate, rapid, selective, qualitative, and quantitative detection of analytes. Their ease of use, low-cost production, portability, and nondestructive measurement techniques also enable on-site detection of analytes. For this reason, biosensors find many applications in food safety and quality assessments. The detection mechanisms of biosensors can be varied with the use of different transducers, such as optical, electrochemical, or mechanical. These options provide a more appropriate selection of the biosensors for the intended use. In this review, recent studies focusing on the fabrication of biosensors for food safety or food quality purposes are summarized. To differentiate the detection mechanisms, the review is divided into sections based on the transducer type used.

Cicada Wing Inspired Template-Stripped SERS Active 3D Metallic Nanostructures for the Detection of Toxic Substances

This article introduces a bioinspired, cicada wing-like surface-enhanced Raman scattering (SERS) substrate based on template-stripped crossed surface relief grating (TS-CSRG). The substrate is polarization-independent, has tunable nanofeatures and can be fabricated in a cleanroom-free environment via holographic exposure followed by template-stripping using a UV-curable resin. The bioinspired nanostructures in the substrate are strategically designed to minimize the reflection of light for wavelengths shorter than their periodicity, promoting enhanced plasmonic regions for the Raman excitation wavelength at 632.8 nm over a large area. The grating pitch that enables an effective SERS signal is studied using Rhodamine 6G, with enhancement factors of the order of 1 × 10⁴. Water contact angle measurements reveal that the TS-CSRGs are equally hydrophobic to cicada wings, providing them with potential self-cleaning and bactericidal properties. Finite-difference time-domain simulations are used to validate the nanofabrication parameters and to further confirm the polarization-independent electromagnetic field enhancement of the nanostructures. As a real-world application, label-free detection of melamine up to 1 ppm, the maximum concentration of the contaminant in food permitted by the World Health Organization, is demonstrated. The new bioinspired functional TS-CSRG SERS substrate holds great potential as a large-area, label-free SERS-active substrate for medical and biochemical sensing applications.

Towards a point-of-care SERS sensor for biomedical and agri-food analysis applications: a review of recent advancements

The growing demand for reliable and robust methodology in bio-chemical sensing calls for the continuous advancement of sensor technologies. Over the last two decades, surface-enhanced Raman spectroscopy (SERS) has emerged as one of the most promising analytical techniques for sensitive and trace analysis or detection in biomedical and agri-food applications. SERS overcomes the inherent sensitivity limitation associated with Raman spectroscopy, which provides vibrational "fingerprint" spectra of molecules that makes it unique and versatile among other spectroscopy techniques. This paper comprehensively reviews the recent advancements of SERS for biomedical, food and agricultural applications over the last 6 years, and we envision that, in the near future, some of these platforms have the potential to be translated as a point-of-care and rapid sensor for real-life end-user applications. The merits and limitations of various SERS sensor designs are analysed and discussed based on critical features such as sensitivity, specificity, usability, repeatability and reproducibility. We conclude by highlighting the opportunities and challenges in the field while stressing the technological gaps to be addressed in realizing commercially viable point-of-care SERS sensors for practical biomedical and agri-food technological applications.

In situ based surface-enhanced Raman spectroscopy (SERS) for the fast and reproducible identification of PHB producers in cyanobacterial cultures

The production of polyhydroxybutyrate (PHB) by autotrophic fermentation of cyanobacteria has received increasing interest in the light of carbon emission reducing process strategies. Biotechnological approaches are in development to optimize the yield of PHB, including adapted cultivation media, characterized by a limitation of key nutrients: cyanobacteria accumulate PHB as energy storage molecules under limited growth conditions. Since there is an increasing demand for fast, simple and reliable analytics, we report the establishment of surface enhanced Raman spectroscopy (SERS) as a suitable monitoring tool for up scaled PHB production processes. Both, pure Ag-colloids mixed with bacterial culture, and in situ prepared colloids (Ag-Synechocystis), generated on the cell surface directly, were successfully applied and evaluated for this purpose. SERS measurements with in situ prepared Ag-colloids improved the reproducibility of Raman signals from 54.8% to 93.9%. The measurement time could be reduced significantly, completing our secondary goal. The quality of classically and in situ prepared Ag-colloids was monitored by zeta potential measurements and scanning electron microscopy (SEM) respectively. For data interpretation and statistical model-building an in house written code in the open source software RStudio was implemented. It was applied for the differentiation of PHB producers at the cellular level, revealing heterogeneities within sample groups regarding the PHB amount accumulated. The results obtained using the statistical model were validated as well and were complementary to the reference HPLC analysis. Therefore, a fast and reliable identification in situ SERS tool for the selection of the most promising cyanobacterial PHB production was established.

Application of surface-enhanced Raman spectroscopy in fast detection of toxic and harmful substances in food

Surface-enhanced Raman spectroscopy (SERS) is being considered as a powerful technique in the area of food safety due to its rapidity, sensitivity, portability, and non-destructive features. This review aims to provide a comprehensive understanding of SERS applications in fast detection of toxic and harmful substances in food matrix. The enhancement mechanism of SERS, classification of active substrates, detection methods, and their advantages and disadvantages are briefly discussed in the review. The latest research progress of fast SERS detection of food-borne pathogens, mycotoxins, shellfish toxins, illegal food additives, and drug residues are highlighted in sections of the review. According to the current status of SERS detection of food-derived toxic and harmful substances, the review comes up with certain problems to be urgently resolved in SERS and brings up the perspectives on the future directions of SERS based biosensors.

Rapid capture and SERS detection of triclosan using a silver nanoparticle core - protein satellite substrate

Triclosan (TCS) is a synthetic antimicrobial compound that has been widely used in consumer products. However, increasing evidence suggests adverse effects of TCS to human health and environment, raising great public concerns. The existing methods for detecting TCS are limited to time-consuming and complicated procedure. Here, we developed a rapid method for capture and detection of TCS using surface-enhanced Raman spectroscopy (SERS) based on a silver nanoparticle (Ag NP) core - protein satellite nanostructure. Bovine serum albumin (BSA) assembled on Ag NPs as satellites configuration could anchor a large number of TCS molecules close to the surface of Ag NPs, producing amplified SERS signals. As low as 50 nM TCS standard was successfully detected within 30 min. We also demonstrated its capability for TCS detection in pond water. The developed SERS method holds a great promise for rapid screening of TCS in environmental and food samples.

Local anomaly detection and quantitative analysis of contaminants in soybean meal using near infrared imaging: The example of non-protein nitrogen

The melamine scandal indicates that traditional targeted detection methods only detect the specifically listed forms of contamination, which leads to the failure to identify new adulterants in time. In order to deal with continually changing forms of adulterations in food and feed and make up for the inadequacy of targeted detection methods, an untargeted detection method based on local anomaly detection (LAD) using near infrared (NIR) imaging was examined in this study. In the LAD method, with a particular size of window filter and at a 99% level of confidence, a specific value of Global H (GH, modified Mahalanobis distance) can be used as a threshold for anomalous spectra detection and quantitative analysis. The results showed an acceptable performance for the detection of contaminations with the advantage of no need of building a 'clean' library. And, a high coefficient of determination (R2LAD = 0.9984 and R2PLS-DA = 0.9978) for the quantitative analysis of melamine with a limit of detection lower than 0.01% was obtained. This indicates that the new strategy of untargeted detection has the potential to move from passive to active for food and feed safety control.

Ag@BiOCl super-hydrophobic nanostructure for enhancing SERS detection sensitivity

Surface-enhanced Raman scattering (SERS) has received widespread attention in the rapid detection of trace substances. The super-hydrophobic surface of structures has a significant impact on improving SERS performance. Usually a low concentration of objective molecules is randomly distributed in a large area on a non-hydrophobic SERS substrate, resulting in the Raman signals of the molecules not being easily detected. As a solution, a super-hydrophobic surface can gather a large number of probe molecules around the plasmon hot spots to effectively improve Raman SERS detection sensitivity. In this work, a chloride super-hydrophobic surface is fabricated, for the first time, by a simple and low-cost method of combining surface hydrophobic structures with surface modification. The dispersed and uniform hierarchical Ag@BiOCl nanosheet (Ag@BiOCl NSs) substrate has a higher surface-to-volume ratio and rich nano-gap. Such a chip with a high static contact angle of 157.4° exhibits a Raman signal detection limit of R6G dyes up to 10⁻⁹ M and an enhancement factor up to 10⁷. This SERS chip with a super-hydrophobic surface offers great potential in practical applications owing to its simple fabricating process, low cost, large area, and high sensitivity.

This large-area hierarchical Ag@BiOCl NSs SERS chip with a super-hydrophobic surface offers a great advantage in further enhancing SERS detection sensitivity.

A microfluidic device enabling surface-enhanced Raman spectroscopy at chip-integrated multifunctional nanoporous membranes

A three-dimensional microfluidic chip that combines sample manipulation and SERS detection on-chip was developed. This was successfully achieved by chip integration of a nanoporous polycarbonate track-etched (PCTE) membrane which connects microfluidic channels on two different levels with each other. The membrane fulfills two functions at the same time. On the one hand, it enables sample enrichment by selective electrokinetic transport processes through the membrane. On the other hand, the silver nanoparticle-coated backside of the same membrane enables SERS detection of the enriched analytes. The SERS substrate performance and the electrokinetic transport phenomena were studied using Rhodamine B (RhB) by Raman microscopy and fluorescence video microscopy. After system validation, the approach was attested by on-chip processing of a complex food sample. In a proof-of-concept study, the microfluidic device with the SERS substrate membrane was used to detect a concentration of 1 ppm melamine (705 cm^-1) in whole milk. Electrokinetic transport across the nanoporous SERS substrate facilitates the extraction of analyte molecules from a sample channel into a detection channel via a potential gradient, thus easily removing obscuring compounds present in the sample matrix. The SERS signal of the analyte could be significantly increased by on-target sample drying. This was achieved by guiding an additional gas flow over the membrane which further extends the microfluidic functionality of the chip device. The proposed method possesses the advantages of combining a rapid (within 15 min) sample clean-up using electrokinetic transport in a three-dimensional microfluidic device which is highly suitable for sensitive and selective SERS detection of chemical and biological analytes. Graphical Abstract.

Challenges in SERS-based pesticide detection and plausible solutions

Surface-enhanced Raman spectroscopy (SERS) can be used for the detection of trace amounts of pesticides in foods to ensure consumer safety. In this perspective, we highlight the trends of SERS-based assays in pesticide detection and the various challenges associated with their selectivity, reproducibility, and nonspecific binding. We also discuss and compare the target analyte capture techniques, such as the use of antibodies, aptamers, and molecularly imprinted polymers (MIPs), coupled with SERS to overcome the drawbacks as mentioned above. In addition, issues related to the nonspecific binding of analytes and its potential solution are discussed.

A SERS approach for rapid detection of microRNA-17 in the picomolar range

Epigenetic biomarkers are powerful tools for early disease detection and are particularly useful for elusive conditions like preeclampsia. Predicting preeclampsia at an early stage is one of the most important goals of maternal-fetal medicine. To this end, recent studies have identified microRNAs-such as microRNA-17-as early biomarkers for preeclampsia. Yet clinical applications are lagging, owing in part to the sensing challenges presented by the biomarkers' small size and complex environment. Surface enhanced Raman spectroscopy (SERS) is an emergent optical technique that is recognized for its potential to overcome these challenges. In this study, DNA functionalized nanoparticles were designed as probes to capture and quantify miRNA-17 in solution. SERS was used to determine the presence and concentration of miRNA-17 based on the formation of plasmonic nanoparticle aggregates. The miRNA-17 assay was tested at concentrations of 1 pM to 1 nM in both PBS and a representative complex biological sample. In both situations the assay was unaffected by non-complementary microRNA samples. These results demonstrate SERS's specificity and sensitivity for a new biomarker (miRNA-17) that may ultimately be used in a detection platform for early diagnosis of preeclampsia.

Rapid fabrication of three-dimensional flower-like gold microstructures on flexible substrate for SERS applications

In this work, hierarchical flower-like gold microstructures (HFGMs) are synthesized on a flexible PET film substrate by electrochemical deposition method as a SERS sensor without surfactant or directing agent. The effects of deposition current and electrolyte concentration on morphology and SERS performance are discussed to find the optimal preparation conditions. SERS activity of samples with different morphologies was investigated by comparing experiments and the mechanism was discussed. It shows the HFGMs with 3D nanoflakes and nanosheet tips present outstanding SERS activity with ultrasensitive detection limits. The lowest concentration of R6G that can be detected is 10^-10 M, and the characteristic signals of thiram can be detected as low as 0.1 ppm. The HFGMs substrate show great potential of application in trace detection by SERS.

Melamine and cyanuric acid exposure and kidney injury in US children

BACKGROUND

Melamine and cyanuric acid, which are currently used in a variety of common consumer products and present in foods, have been implicated in the development of urolithiasis and acute kidney injury in Chinese children. To determine whether US children have measurable concentrations of these chemicals in their bodies and whether they are at greater risk of acute kidney injury, we measured melamine and cyanuric acid exposure in a cohort of US children and determined their relationship with markers of kidney injury.

METHODS

We measured urinary melamine and cyanuric acid in a convenience sample of 109 children (4 months - 8 years) from Seattle, WA and New York City, NY using liquid chromatography with tandem mass spectrometry. We measured several urinary markers of kidney injury: fatty acid binding protein 3 (FABP3), kidney injury molecule 1 (KIM1), neutrophil gelatinase-associated lipocalin (NGAL) using Luminex xMAP methods, and urine urea was measured using standard laboratory methods. We described urinary melamine and cyanuric acid concentrations and assessed predictors of the exposures. We used multivariable linear regression to assess relationships between melamine/cyanuric acid and kidney injury markers in unadjusted and adjusted (creatinine, age, sex) analyses.

RESULTS

Melamine and cyanuric acid were above the limit of detection (LOD) in 78% and 95% of all samples, respectively. The mean concentrations (SD) for melamine and cyanuric acid were 27.4 ng/ml (141.9 ng/ml) and 35.3 ng/ml (42.4 ng/ml). In unadjusted analyses, we observed statistically significant increases in the percentages of FABP3 and KIM1 in relation to a one log unit change in melamine and cyanuric acid, respectively. In adjusted analyses, we observed a 55% (95% CI 0, 141) increase in KIM1 in relation to a one log unit increase in cyanuric acid.

CONCLUSIONS

US children have detectable concentrations of melamine and cyanuric acid in urine, and these concentrations are higher than those reported in children from other countries. This is a novel finding that improves upon previous exposure estimates using questionnaires only and suggests widespread exposure in the population. Cyanuric acid is associated with increased KIM 1 concentrations, suggesting kidney injury. Given the potential widespread exposure, future analyses should examine melamine and cyanuric acid in relation to chronic kidney disease and markers of kidney injury in a larger cohort that is representative of the general population.

Enhancing Disease Diagnosis: Biomedical Applications of Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) has recently gained increasing attention for the detection of trace quantities of biomolecules due to its excellent molecular specificity, ultrasensitivity, and quantitative multiplex ability. Specific single or multiple biomarkers in complex biological environments generate strong and distinct SERS spectral signals when they are in the vicinity of optically active nanoparticles (NPs). When multivariate chemometrics are applied to decipher underlying biomarker patterns, SERS provides qualitative and quantitative information on the inherent biochemical composition and properties that may be indicative of healthy or diseased states. Moreover, SERS allows for differentiation among many closely-related causative agents of diseases exhibiting similar symptoms to guide early prescription of appropriate, targeted and individualised therapeutics. This review provides an overview of recent progress made by the application of SERS in the diagnosis of cancers, microbial and respiratory infections. It is envisaged that recent technology development will help realise full benefits of SERS to gain deeper insights into the pathological pathways for various diseases at the molecular level.

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.

One-step wet-chemical synthesis of ternary ZnO/CuO/Co3O4 nanoparticles for sensitive and selective melamine sensor development

Using one-step wet-chemically synthesized ternary ZnO/CuO/Co₃O₄ nanoparticles (NPs) fabricated GCE sensor probe, a selective and sensitive melamine chemical sensor was developed by electrochemical approach, which exhibited the highest sensitivity, better repeatability, broad linear dynamic range, good linearity, fast response time, and lowest detection limit.

Superhydrophobic SERS substrates based on silver dendrite-decorated filter paper for trace detection of nitenpyram

In the present work, highly sensitive Raman detection of nitenpyram using superhydrophobic filter paper as substrates is introduced. The process is simple, and efficient. By sequentially coating silver dendrites and Octyltrimethoxysilane (OTMOS) on filter paper, we produced highly active surface-enhanced Raman scattering (SERS) substrates which show advancing and receding water contact angles of θ_A/θ_R = 159°/156°. Nitenpyram, a type of pesticides popularly used in agriculture, can be easily detected with the detection limit as low as 1 nM using the superhydrophobic filter paper as SERS substrates, which validates their use in Raman applications.

Rapid, On-Site, Ultrasensitive Melamine Quantitation Method for Protein Beverages Using Time-Resolved Fluorescence Detection Paper

To ensure protein beverage safety and prevent illegal melamine use to artificially increase protein content, a rapid, on-site, ultrasensitive detection method for melamine must be developed because melamine is detrimental to human health. Herein, an ultrasensitive time-resolved fluorescence detection paper (TFDP) was developed to detect melamine in protein beverages within 15 min using a one-step sample preparation. The lower limits of detection were 0.89, 0.94, and 1.05 ng/mL, and the linear ranges were 2.67-150, 2.82-150, and 3.15-150 ng/mL (R2 > 0.982) for peanut, walnut, and coconut beverages, respectively. The recovery rates were 85.86-110.60% with a coefficient of variation <7.80% in the spiking experiment. A high specificity was observed in the interferent experiment. When detecting real protein beverage samples, the TFDP and ultraperformance liquid chromatography-tandem mass spectrometer (UPLC-MS/MS) results were consistent. This method is a promising alternative for rapid, on-site detection of melamine in beverages.

A Surface Plasmon Resonance-Based Optical Fiber Probe Fabricated with Electropolymerized Molecular Imprinting Film for Melamine Detection

Molecularly imprinted polymer (MIP) films prepared by bulk polymerization suffer from numerous deficiencies, including poor mass transfer ability and difficulty in controlling reaction rate and film thickness, which usually result in poor repeatability. However, polymer film synthesized by electropolymerization methods benefit from high reproducibility, simplicity and rapidity of preparation. In the present study, an Au film served as the refractive index-sensitive metal film to couple with the light leaked out from optical fiber core and the electrode for electropolymerizing MIP film simultaneously. The manufactured probe exhibited satisfactory sensitivity and specificity. Furthermore, the surface morphology and functional groups of the synthesized MIP film were characterized by Atomic Force Microscopy (AFM) and Fourier transform infrared microspectroscopy (FTIR) for further insights into the adsorption and desorption processes. Given the low cost, label-free test, simple preparation process and fast response, this method has a potential application to monitor substances in complicated real samples for out-of-lab test in the future.

Bioanalytical applications of surface-enhanced Raman spectroscopy: de novo molecular identification

Surface enhanced Raman scattering (SERS) has become a powerful technique for trace analysis of biomolecules. The use of SERS-tags has evolved into clinical diagnostics, the enhancement of the intrinsic signal of biomolecules on SERS active materials shows tremendous promise for the analysis of biomolecules and potential biomedical assays. The detection of the de novo signal from a wide range of biomolecules has been reported to date. In this review, we examine different classes of biomolecules for the signals observed and experimental details that enable their detection. In particular, we survey nucleic acids, amino acids, peptides, proteins, metabolites, and pathogens. The signals observed show that the interaction of the biomolecule with the enhancing nanostructure has a significant influence on the observed spectrum. Additional experiments demonstrate that internal standards can correct for intensity fluctuations and provide quantitative analysis. Experimental methods that control the interaction at the surface are providing for reproducible SERS signals. Results suggest that combining advances in methodology with the development of libraries for SERS spectra may enable the characterization of biomolecules complementary to other existing methods.

Uniform Microgels Containing Agglomerates of Silver Nanocubes for Molecular Size-Selectivity and High SERS Activity

Surface-enhanced Raman scattering (SERS) is a promising technique for molecular analysis as the molecular fingerprints (Raman spectra) are amplified to detectable levels compared with common spectroscopy. Metal nanostructures localize electromagnetic field on their surfaces, which can lead to dramatic increase of Raman intensity of molecules adsorbed. However, the metal surfaces are prone to contamination, thereby requiring pretreatment of samples to remove adhesive molecules. To avoid the pretreatment and potentially achieve point-of-care (POC) analysis, we have developed SERS-active microgels using the droplet-microfluidic system. As the microgels are composed of water-swollen network with consistent mesh size, they selectively allow diffusion of molecules smaller than the mesh, thereby excluding large adhesives. To render the microgels highly SERS-active, we destabilize silver nanocubes to form agglomerates, which are embedded in the matrix of microgels. The nanogaps in the agglomerates provide high sensitivity in Raman measurement and size-selective permeability of the microgel matrix obviates the pretreatment of samples. To validate the functions, we demonstrate the direct detection of Aspirin dissolved in whole blood without any pretreatment.