Surface-enhanced Raman scattering based on noble metal nanoassemblies for detecting harmful substances in food

Residues of harmful substances in food can severely damage human health. The content of these substances in food is generally low, making detection difficult. Surface-enhanced Raman scattering (SERS), based on noble metal nanomaterials, mainly gold (Au) and silver (Ag), has exhibited excellent capabilities for trace detection of various substances. Noble metal nanoassemblies, in particular, have extraordinary flexibility and tunable optical properties, which cannot be offered by single nanoparticles (NPs). These nanoassemblies, with their various morphologies synthesized using NPs through artificially induced self-assembly or template-driven preparation, can significantly enhance the local electric field and create "hot spots" due to the gaps between adjacent NPs. Consequently, the SERS properties of NPs become more prominent, leading to improved performance in the trace detection of various substances and detection limits that are considerably lower than the current relevant standards. Noble metal nanoassemblies show promising potential in ensuring food safety. This review discusses the synthesis methods and SERS properties of noble metal nanoassemblies and then concentrates on their application in detecting biotoxins, drug residues, illegal additives, and heavy metals. The study provides valuable references for further research into the application of nanoassemblies in food safety detection.

Nanotechnology-based optical sensors for Baijiu quality and safety control

Baijiu quality and safety have received considerable attention owing to the gradual increase in its consumption. However, owing to the unique and complex process of Baijiu production, issues leading to quality and safety concerns may occur during the manufacturing process. Therefore, establishing appropriate analytical methods is necessary for Baijiu quality assurance and process control. Nanomaterial (NM)-based optical sensing techniques have garnered widespread interest because of their unique advantages. However, comprehensive studies on nano-optical sensing technology for quality and safety control of Baijiu are lacking. In this review, we systematically summarize NM-based optical sensor applications for the accurate detection and quantification of analytes closely related to Baijiu quality and safety. Furthermore, we evaluate the sensing mechanisms for each application. Finally, we discuss the challenges nanotechnology poses for Baijiu analysis and future trends. Overall, nanotechnological approaches provide a potentially useful alternative for simplifying Baijiu analysis and improving final product quality and safety.

Qualitative and quantitative studies of phthalates in extra virgin olive oil (EVOO) by surface-enhanced Raman spectroscopy (SERS) combined with long short term memory (LSTM) neural network

Phthalates are commonly used plasticizers in the plastics industry, and have received extensive attention due to their reproductive toxicity. Since phthalates are lipophilic solutions, phthalates can easily migrate from packaging to edible oils. This study synthesized stable and sensitive Gold Nanostars as SERS substrates to conduct qualitative and quantitative analysis of two common phthalates, dibutyl phthalate and di(2-ethylhexyl) phthalate. Two ethanol standard solutions and actual oil solutions of phthalates at different concentrations (10, 5, 1, 0.5, 0.1, 0.02 mg/kg) were prepared. After dimension reduction, LSTM achieved the accuracy of 98% for pure EVOO and EVOO adulterated with different types of phthalates. In terms of quantification, LSTM demonstrates great predictive performance with Rp2 greater than 0.97 and the ratio of performance to deviation greater than 5. These results have certain guiding significance for the analysis of plasticizers in edible oil.

Development of an automated Raman system and use of principal component analysis to classify real and counterfeit liquors

We developed an automated Raman measurement platform for the customized design of various solution containers. We used the software LabVIEW to integrate the entire automatic measurement process. By designing an intuitive human-machine interface, the user only needs to input a few setting parameters and can efficiently operate the machine in automation mode for an array of solutions containing real or counterfeit liquors such as kaoliang liquor, vodka, rum, gin, rice wine, ethanol, and methanol. In this study, data from various alcoholic beverage solutions were subjected to principal component analysis (PCA) to distinguish from the low-concentration counterfeit liquors (methanol <50 g L-1). Moreover, several brands of liquors with the same alcohol concentration were successfully classified into different groups based on a combination of Raman spectroscopy and PCA analysis.

Recent advancements in nanomaterial based optical detection of food additives: a review

Food additives have become a critical component in the food industry. They are employed as preservatives to decelerate the negative effects of environmental and microbial factors on food quality. Currently, food additives are used for a variety of purposes, including colorants, flavor enhancers, nutritional supplements, etc., owing to improvements in the food industry. Since the usage of food additives has increased dramatically, the efficient monitoring of their acceptable levels in food products is quite necessary to mitigate the problems associated with their inappropriate use. The traditional methods used for detecting food additives are generally based on standard spectroscopic and chromatographic techniques. However, these analytical techniques are limited by their high instrumentation cost and time-consuming procedures. The emerging field of nanotechnology has enabled the development of highly sensitive and specific sensors to analyze food additives in a rapid manner. The current article emphasizes the need to detect various food additives owing to their potential negative effects on humans, animals, and the environment. In this article, the role of nanomaterials in the optical sensing of food additives has been discussed owing to their high accuracy, ease-of-use, and excellent sensitivity. The applications of nanosensors for the detection of various food additives have been elaborated with examples. The current article will assist policymakers in developing new rules and regulations to mitigate the adverse effects of toxic food additives on humans and the environment. In addition, the prospects of nanosensors for the optical detection of food additives at a commercial scale have been discussed to combat their irrational use in the food industry.

Design, Fabrication, and Applications of SERS Substrates for Food Safety Detection: Review

Sustainable and safe food is an important issue worldwide, and it depends on cost-effective analysis tools with good sensitivity and reality. However, traditional standard chemical methods of food safety detection, such as high-performance liquid chromatography (HPLC), gas chromatography (GC), and tandem mass spectrometry (MS), have the disadvantages of high cost and long testing time. Those disadvantages have prevented people from obtaining sufficient risk information to confirm the safety of their products. In addition, food safety testing, such as the bioassay method, often results in false positives or false negatives due to little rigor preprocessing of samples. So far, food safety analysis currently relies on the enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR), HPLC, GC, UV-visible spectrophotometry, and MS, all of which require significant time to train qualified food safety testing laboratory operators. These factors have hindered the development of rapid food safety monitoring systems, especially in remote areas or areas with a relative lack of testing resources. Surface-enhanced Raman spectroscopy (SERS) has emerged as one of the tools of choice for food safety testing that can overcome these dilemmas over the past decades. SERS offers advantages over chromatographic mass spectrometry analysis due to its portability, non-destructive nature, and lower cost implications. However, as it currently stands, Raman spectroscopy is a supplemental tool in chemical analysis, reinforcing and enhancing the completeness and coverage of the food safety analysis system. SERS combines portability with non-destructive and cheaper detection costs to gain an advantage over chromatographic mass spectrometry analysis. SERS has encountered many challenges in moving toward regulatory applications in food safety, such as quantitative accuracy, poor reproducibility, and instability of large molecule detection. As a result, the reality of SERS, as a screening tool for regulatory announcements worldwide, is still uncommon. In this review article, we have compiled the current designs and fabrications of SERS substrates for food safety detection to unify all the requirements and the opportunities to overcome these challenges. This review is expected to improve the interest in the sensing field of SERS and facilitate the SERS applications in food safety detection in the future.

Substrate mediated properties of gold monolayers on SiC

In light of their unique physicochemical properties two-dimensional metals are of interest in the development of next-generation sustainable sensing and catalytic applications. Here we showcase results of the investigation of the substrate effect on the formation and the catalytic activity of representative 2D gold layers supported by non-graphenized and graphenized SiC substrates. By performing comprehensive density functional theory (DFT) calculations, we revealed the epitaxial alignment of gold monolayer with the underlying SiC substrate, regardless of the presence of zero-layer graphene or epitaxial graphene. This is explained by a strong binding energy (∼4.7 eV) of 2D Au/SiC and a pronounced charge transfer at the interface, which create preconditions for the penetration of the related electric attraction through graphene layers. We then link the changes in catalytic activity of substrate-supported 2D Au layer in hydrogen evolution reaction to the formation of a charge accumulation region above graphenized layers. Gold intercalation beneath zero-layer graphene followed by its transformation to quasi-free-standing epitaxial graphene is found to be an effective approach to tune the interfacial charge transfer and catalytic activity of 2D Au. The sensing potential of substrate-supported 2D Au was also tested through exploring the adsorption behaviour of NH3, NO2 and NO gas molecules. The present results can be helpful for the experimental design of substrate-supported 2D Au layers with targeted catalytic activity and sensing performance.

SERS-based antibiotic susceptibility testing: Towards point-of-care clinical diagnosis

Emerging antibiotic resistant bacteria constitute one of the biggest threats to public health. Surface-enhanced Raman scattering (SERS) is highly promising for detecting such bacteria and for antibiotic susceptibility testing (AST). SERS is fast, non-destructive (can probe living cells) and it is technologically flexible (readily integrated with robotics and machine learning algorithms). However, in order to integrate into efficient point-of-care (PoC) devices and to effectively replace the current culture-based methods, it needs to overcome the challenges of reliability, cost and complexity. Recently, significant progress has been made with the emergence of both new questions and new promising directions of research and technological development. This article brings together insights from several representative SERS-based AST studies and approaches oriented towards clinical PoC biosensing. It aims to serve as a reference source that can guide progress towards PoC routines for identifying antibiotic resistant pathogens. In turn, such identification would help to trace the origin of sporadic infections, in order to prevent outbreaks and to design effective medical treatment and preventive procedures.

Smartphone-Integrated Photoacoustic Analytical Device for Point-of-Care Testing of Food Contaminant Azodicarbonamide

Azodicarbonamide (ADA) is widely used as a flour additive due to its oxidizing and bleaching properties, but it reacts with wet flour during heat processing and is easily decomposed into semicarbazide with genotoxicity and carcinogenicity. In order to improve the efficiency of food safety supervision and expand the scope of food safety control, it is of great significance to develop a facile method for point-of-care testing (POCT) of ADA. Herein, a field-portable and universal smartphone-based photoacoustic (PA) integration device is constructed for quantitative POCT of ADA in flour. The recognition probe Prussian blue with favorable stability is loaded on a flexible substrate for fabricating a portable test strip. In the presence of target ADA, the PA signal changes driven by a modulated 808 nm laser beam can be conveniently collected through the recording application (Audio Lab) of the smartphone. By combining the economic test strip and portable PA device with smartphone readout, it not only greatly simplifies the operation steps but also dramatically reduces the size and cost of the instrument. There is a favorable linear relationship between the PA signal and ADA concentration in the range of 10-200 μmol L^-1 (R² = 0.9928), and a detection limit of 5 μmol L^-1 obtained is much lower than the maximum allowable ADA level in the extract of flour (388 μmol L^-1). The present miniature PA device with strong POCT ability holds enormous public health significance and economic value in the field of food safety, especially in resource-limited settings.

Recent Developments in Surface-Enhanced Raman Spectroscopy and Its Application in Food Analysis: Alcoholic Beverages as an Example

Surface-enhanced Raman spectroscopy (SERS) is an emerging technology that combines Raman spectroscopy and nanotechnology with great potential. This technology can accurately characterize molecular adsorption behavior and molecular structure. Moreover, it can provide rapid and sensitive detection of molecules and trace substances. In practical application, SERS has the advantages of portability, no need for sample pretreatment, rapid analysis, high sensitivity, and ‘fingerprint’ recognition. Thus, it has great potential in food safety detection. Alcoholic beverages have a long history of production in the world. Currently, a variety of popular products have been developed. With the continuous development of the alcoholic beverage industry, simple, on-site, and sensitive detection methods are necessary. In this paper, the basic principle, development history, and research progress of SERS are summarized. In view of the chemical composition, the beneficial and toxic components of alcoholic beverages and the practical application of SERS in alcoholic beverage analysis are reviewed. The feasibility and future development of SERS are also summarized and prospected. This review provides data and reference for the future development of SERS technology and its application in food analysis.

Surface-Enhanced Raman Spectroscopy Substrates for Food Safety and Quality Analysis

Surface-enhanced Raman spectroscopy (SERS) has been identified as a fundamental surface-sensitive technique that boosts Raman scattering by adsorbing target molecules on specific surfaces. The application of SERS highly relies on the development of smart SERS substrates, and thus the fabrication of SERS substrates has been constantly improved. Herein, we investigate the impacts of different substrates on SERS technology including plasmonic metal nanoparticles, semiconductors, and hybrid systems in quantitative food safety and quality analysis. We first discuss the fundamentals, substrate designs, and applications of SERS. We then provide a critical review of the recent progress of SERS in its usage for screening and detecting chemical and biological contaminants including fungicides, herbicides, insecticides, hazardous colorants, and biohazards in food samples to assess the analytical capabilities of this technology. Finally, we investigate the future trends and provide practical techniques that could be used to fulfill the requirements for rapid analysis of food at a low cost.

MoS2-Based Substrates for Surface-Enhanced Raman Scattering: Fundamentals, Progress and Perspective

Surface-enhanced Raman scattering (SERS), as an important tool for interface research, occupies a place in the field of molecular detection and analysis due to its extremely high detection sensitivity and fingerprint characteristics. Substantial efforts have been put into the improvement of the enhancement factor (EF) by way of modifying SERS substrates. Recently, MoS2 has emerged as one of the most promising substrates for SERS, which is also exploited as a complementary platform on the conventional metal SERS substrates to optimize the properties. In this minireview, the fundamentals of MoS2-related SERS are first explicated. Then, the synthesis, advances and applications of MoS2-based substrates are illustrated with special emphasis on their practical applications in food safety, biomedical sensing and environmental monitoring, together with the corresponding challenges. This review is expected to arouse broad interest in nonplasmonic MoS2-related materials along with their mechanisms, and to promote the development of SERS studies.

Four MOFs with isomeric ligands as fluorescent probes for highly selective, sensitive and stable detection of antibiotics in water

Four complexes showed excellent discriminative probes for cefixime (CEF) and tetracycline (TEC) based on their sensitive fluorescence quenching. The PET and IFE effects resulted in high sensitivity and selectivity for the detection of CEF and TEC.

A series of isostructural lanthanide metal-organic frameworks: effective fluorescence sensing for Fe3+, 2,4-DNP and 4-NP

Because of the fluorescence properties, lanthanide metal-organic frameworks (Ln-MOFs) materials have potential application in the detections of metal ions and nitro-aromatic explosives. Herein, a series of isostructural Ln-MOFs [Ln2(PIA)3(DMF)3(CH3OH)] (JLU-MOF201-Ln,...

A colorimetric sensing platform for azodicarbonamide detection in flour based on MnO2 nanosheets oxidative system

Azodicarbonamide (ADA), as a dough conditioner food additive in flour, can be turned into toxic biurea and semicarbazide after high temperature processing. Hence, the using of ADA in food material should be strictly controlled, and the detection of ADA is very important for consumers' safety and health. Herein, a simple and fast colorimetric strategy has been developed for ADA detection based on the MnO₂ nanosheets-3,3',5,5'-tetramethylbenzidine (TMB)-glutathione (GSH) as oxidative sensing system (MnO₂-TMB-GSH). Since the ADA can selectively react with GSH via oxidizing the sulfydryl (-SH) group of GSH to disulfide bond (S-S), which makes GSH unable to reduce MnO₂ nanosheets and restore its oxidase-like activity. The absorbance changes of the TMB solution depended on ADA content. The MnO₂-TMB-GSH colorimetric platform can detect the ADA with a linear range of 10 μmol L^-1 (11.6 ppm) to 400 μmol L^-1 (464 ppm), and the limit of detection (LOD) is 3.3 μmol L^-1 (3.51 ppm). Some potential interferences in real sample were tested and did not affect the MnO₂-TMB-GSH colorimetric platform for ADA detection. Furthermore, the sensing platform was applied for detecting ADA in real flour sample with a recovery of 96%-105% (RSD < 5%). This colorimetric method can effectively and rapidly detect ADA additives in flour less than the prescribed standard (45 mg kg^-1), which shows a great potential for visualization analysis and on-site detection of ADA in flour. A simple and fast colorimetric strategy has been developed for azodicarbonamide (ADA) detection based on the MnO₂ nanosheets-3,3',5,5'-tetramethylbenzidine (TMB)-glutathione (GSH) as oxidative sensing system (MnO₂-TMB-GSH).

Silver melamine thin film as a flexible platform for SERS analysis

New SERS detection platforms are required for the quick and easy preparation of sensing devices for food, agriculture, and environmental science. For quantitative sensing, it is important that a sensing material, in addition to efficient sensing, provides extraction and concentration of the target molecules such as toxic pesticides or healthy vitamins. We design such films adopting the Liesegang rings formation process that includes the reaction-diffusion of silver nitrate and melamine followed by the precipitation of different intermediates and their reduction by light in a pectin medium. Surprisingly, we find that the presence of melamine provides an excellent substrate for the extraction of pollutants at the solid-liquid interface giving rise to a powerful but easy and fast method for the quantification of fruits' quality. The complex silver and melamine containing films show high sensitivity even at relatively low silver concentrations.

Visual determination of azodicarbonamide in flour by label-free silver nanoparticle colorimetry

A very practical and competitive sensing strategy for the detection of azodicarbonamide in flour samples was developed by using label-free Ag NPs as a colorimetric probe. Well-dispersed Ag NPs in suspension can form aggregates upon reacting with glutathione (GSH) via Ag-SH covalent bonds and electrostatic attraction, with the color changing from bright yellow to red. However, azodicarbonamide can oxidize the -SH of GSH, preventing the aggregation of Ag NPs. Under the optimum conditions, the A₅₅₀/A₃₉₈ of Ag NPs is linearly related to the concentration of azodicarbonamide in the range of 0.33 μM to 1.7 μM. The proposed method can be used for the detection of azodicarbonamide in flour, with a detection limit of 0.09 μM and recovery between 95% and 97.4% (RSD < 6%). When the azodicarbonamide concentration reaches 0.33 μM, the color change can be detected by the naked eye.

Identification of 15 Phthalate Esters in Commercial Cheese Powder via Cyclodextrin-Promoted Fluorescence Detection

A challenge for detecting phthalates in commercial products such as cheese powders is that the composition of the products is highly complex, and current methods for detection rely on gas chromatography-mass spectrometry, which is not portable and cannot be used by individual consumers at a time and place of their choosing. Herein, we report the development of a new method for phthalate detection in cheese powder using cyclodextrin-promoted fluorescence detection, in which the presence of the phthalate analytes leads to highly analyte-specific changes in the fluorescence emission signal of a fluorophore bound in a cyclodextrin cavity. This method relies on subtle changes in the analyte affinity for the fluorophore and the cyclodextrin cavity and provides for markedly more straightforward sample preparation procedures and an extremely rapid read-out signal, with potential for the development of portable fluorescence sensors. Using this method, we were able to detect 15 phthalate esters with highly analyte-specific responses and at concentrations as low as 0.12 μM, which is well below regulatory levels of concern. Computational investigations strongly support the observed experimental trends.

Nontargeted Detection Methods for Food Safety and Integrity

Nontargeted workflows for chemical hazard analyses are highly desirable in the food safety and integrity fields to ensure human health. Two different analytical strategies, nontargeted metabolomics and chemical database filtering, can be used to screen unknown contaminants in food matrices. Sufficient mass and chromatographic resolutions are necessary for the detection of compounds and subsequent componentization and interpretation of candidate ions. Analytical chemistry–based technologies, including gas chromatography–mass spectrometry (GC-MS), liquid chromatography–mass spectrometry (LC-MS), nuclear magnetic resonance (NMR), and capillary electrophoresis–mass spectrometry (CE-MS), combined with chemometrics analysis are being used to generate molecular formulas of compounds of interest. The construction of a chemical database plays a crucial role in nontargeted detection. This review provides an overview of the current sample preparation, analytical chemistry–based techniques, and data analysis as well as the limitations and challenges of nontargeted detection methods for analyzing complex food matrices. Improvements in sample preparation and analytical platforms may enhance the relevance of food authenticity, quality, and safety.