Direct Detection of Toxic Contaminants in Minimally Processed Food Products Using Dendritic Surface-Enhanced Raman Scattering Substrates

Improved Surface-Enhanced Raman Scattering Performance of 2D Ti3C2Tx MXene Embedded in PVDF Film Enabled by Photoinduction and Electric Field Modulation

In this study, we introduce a synergistic approach to enhance the surface-enhanced Raman scattering (SERS) signal in two-dimensional (2D) MXene through photo-irradiation and electric field modulation. Our methodology involves the integration of 2D Ti3C2Tx MXene with piezoelectric polyvinylidene fluoride (PVDF) polymer, resulting in the creation of a free-standing, flexible composite film. On this composite film, a thin layer of Au was deposited. Our flexible substrate was able to sense methylene blue (MB), crystal violet (CV), 4-aminothiophenol (ATP), and melamine. The SERS substrate exhibits low detection limit of 10-8 M MB with a 6.7 × 106 enhancement factor (EF). The SERS substrate enables picomolar (pM) detection sensitivity for CV molecules with an EF of 9.2 × 109. Furthermore, the introduction of photo-irradiation leads to an additional ∼3.5-fold enhancement in the SERS signal, which is attributed to the altered work function and defects. The application of mechanical force to the piezoelectric PVDF/Ti3C2Tx film results in a ∼4.5-fold boost in SERS signal due to mechanical force-induced electrical energy. The fabrication strategy employed here for producing a flexible piezoelectric PVDF/Ti3C2Tx film holds significant promise for expanding the potential application of 2D MXene in rapid, on-site sensing scenarios.

A novel 2D-GO@WS2 electrochemical platform for the determination of thiram fungicide

In this paper, the determination of Thiram fungicide by a novel modified screen-printed carbon electrode (SPCE) fabricated modifying the working electrode (WE) with 2D-GO/WS2 nanohybrid composites, is reported. Scanning electron microscopy (SEM), Raman spectroscopy, and fluorescence analysis (PL) were used to reveal the morphological and microstructural characteristics of the 2D-GO/WS2 nanohybrids with different graphene oxide:tungsten disulphide (GO:WS2) ratio. Electrochemical characterization demonstrated that the 2D-WS2/GO nanohybrids having a GO:WS2 ratio = 2:1 shows the highest electrocatalytic activity towards oxidation of Thiram. The developed sensor permits the quantification of Thiram in the linear range 0.083-0.33 µM with a limit of detection (LOD) of 0.02 µM, which is below the legal limits for this fungicide in drinking water or foods.

Determination of thiram in fruit juices using a bacterial cellulose nanocrystal-based SERS substrate

Pesticide residues in agri-foods have risk to human health and one solution is to develop simple and accurate methods for rapid detection. We developed a SERS sensor composed of gold nanoparticles (AuNPs) and bacterial cellulose nanocrystal (BCNC) to detect thiram in fruit juice. BCNC-SO3H was used as a stabilizer to support AuNPs via electrostatic repulsion, fabricating a BCNC-AuNPs SERS substrate with uniformly distributed AuNPs. This BCNC-AuNPs SERS substrate was applied to determine thiram residues in peach juice, apple juice, and grape juice with the limits of detection of 0.036 ppm, 0.044 ppm, and 0.044 ppm, respectively. The whole test took 12 min including sample preparation and analysis. The detection limits meet the maximum residue levels of thiram in fruit juices required by China, Europe and North America, indicating that this BCNC-based substrate could serve as a satisfactory SERS sensor for pesticide residue monitoring in the food supply chain.

Silver decahedral nanoparticles with uniform and adjustable sizes for surface-enhanced Raman scattering-based thiram residue detection

Surface-enhanced Raman scattering (SERS) has been widely used as a sensitive molecular spectroscopy technology in food safety detection. Precise morphology control of plasmonic nanoparticles for high sensitivity and high uniformity SERS substrates remains challenging. Herein, silver decahedral nanoparticles (AgDeNPs) with uniform and adjustable sizes were synthesized by a photochemical seed-mediated method and utilized as SERS substrates for pesticide residue detection. The SERS sensitivity was demonstrated by using 4-mercaptobenzoic acid (4-MBA) as a typical model molecule, and the limit of detection (LOD) reached 1.0 × 10-13 M. The pesticide residue detection of thiram in aqueous solution and on fruit peels was successfully realized; the LODs were 1.0 × 10-11 M and 0.96 ng cm-2, respectively, and SERS repeatability was also proved. Overall, size-tunable AgDeNPs show attractive SERS performances and are expected to hold potential application in sensitive food and environmental safety detection.

Capillary Tube Surface-Enhanced Raman Scattering Substrate and High-Sensitivity Molecule Detection

Surface-enhanced Raman scattering (SERS) greatly improves molecule sensitivity compared with ordinary Raman spectroscopy. To excite and detect SERS efficiently, we fabricated glass-made microcapillary tubes decorated with silver nanoparticles inside them. The capillary tubes work as sample containers, where the required sample volume is in the order of a few nanoliters. The capillary tubes also play the role of optical waveguides. The tubes guide the excitation laser light through them so that the light illuminates whole silver nanoparticles inside the tubes at once. The tubes guide the SERS light to the tube end efficiently. The decoration of silver nanoparticles inside the tubes was performed by the silver mirror reaction. By making the tubes thinner and longer, highly sensitive SERS spectroscopy can be achieved. Our method would be a powerful tool for high-sensitivity molecule detection where the sample volume and concentration are extremely low.

Nanotechnology in food and water security: on-site detection of agricultural pollutants through surface-enhanced Raman spectroscopy

Agricultural pollutants are harmful components threatening human health, wildlife, the environment, and the ecosystem. To avoid their exposure, developing prevention and detection systems with high sensitivity and selectivity is required. Most conventional methods, including molecular and chromatographic techniques, cannot be adopted for outdoor on-site detection even though they can provide sensitive and selective detection. Thus, detection platforms that can provide on-site detection via miniaturized and high throughput systems should be developed. As an alternative method, surface-enhanced Raman scattering (SERS) provides unique information about the substances in the presence of plasmonic nanostructures, and it can be portable with the use of portable detection systems and spectrometers. In this study, on-site detection of agricultural pollutants through SERS is reviewed. Three different types of agricultural pollutants were pointed out. On-site detection of biological pollutants, including bacteria and viruses, is reviewed as the first type of pollutant. As a second type, the detection of pesticides, antibiotics, and additives are focused on as chemical pollutants. The third group includes the detection of microplastics and also nanoparticles from the environment.

Chlorogenic acid inhibits apoptosis in thiram-induced tibial dyschondroplasia via intrinsic pathway

Tibial dyschondroplasia (TD) is a common skeletal disease occurred in growth plate of fast-growing broilers. Thiram is a sort of chemical used for pesticide and fungicide. The excessive use of thiram increased the threat to animal and human health. In this study, we aimed to investigate the therapeutic mechanism of chlorogenic acid (CGA) on thiram-induced tibial dyschondroplasia. Broiler chickens were divided into three different groups, e.g., control, TD, and CGA. CGA was administrated after the induction of TD from 4^th day to 7^th day. Biochemical analysis was performed to detect the content of calcium (Ca) and phosphorus (P). Histological changes and degradation of extracellular matrix were observed through hematoxylin-eosin (H & E) and Masson staining. To further determine the mechanism, TUNEL staining and western blot were also performed to detect the apoptosis changes in growth plate of all groups. The results showed the disproportionation of Ca and P content and upregulation of apoptosis during the development of TD. But, after the administration of CGA, the ratio of Ca:P was upregulated, and the apoptosis was also downregulated. The current study shows the toxic effect of thiram on chickens and suggests that CGA is associated with a mechanism that plays a significant role in apoptosis induced by thiram in poultry industry.

Development of a New Screen-Printed Transducer for the Electrochemical Detection of Thiram

A new transducer based on a screen-printed carbon electrode has been developed for the quantification of thiram. Detection of this fungicide is based on the performance of two enzymes: (1) aldehyde dehydrogenase catalyzes the aldehyde oxidation using NAD+ as a cofactor and simultaneously, (2) diaphorase reoxidizes the NADH formed in the first enzymatic process due to the presence of hexacyanoferrate(III) which is reduced to hexacyanoferrate(II). Taking into account that aldehyde dehydrogenase is inhibited by thiram, the current decreases with pesticide concentration and thiram can be electrochemically quantified below legal limits. The transducer proposed in this work involves the modification of the carbon WE with the co-factors (NAD+ and hexacyanoferrate(III)) required in the enzymatic system. The new device employed in this work allows the detection of 0.09 ppm thiram, a concentration below legal limits (Maximum Residue Limits 0.1–10 ppm).

Adsorption/Desorption Behaviors and SERS Chemical Enhancement of 6-Mercaptopurine on a Nanostructured Gold Surface: The Au20 Cluster Model

Computational approaches are employed to elucidate the binding mechanism and the SERS phenomenon of 6-mercaptopurine (6MP) adsorbed on the tetrahedral Au20 cluster as a simple model for a nanostructured gold surface. Computations are carried out in both vacuum and aqueous environments using a continuum model. In the gaseous phase and neutral conditions, interaction of 6MP with the gold cluster is mostly dominated by a covalent Au-S bond and partially stabilized by the Au⋅⋅⋅H-N coupling. However, in acidic solution, the nonconventional Au⋅⋅⋅H-S hydrogen-bond becomes the most favorable binding mode. The 6MP affinity for gold clusters decreases in the order of vacuum > neutral solution > acidic medium. During the adsorption, the energy gap of Au20 substantially declines, leading to an increase in its electrical conductivity, which can be converted to an electrical noise. Moreover, such interaction is likely a reversible process and triggered by either the low pH in sick tissues or the presence of cysteine residues in protein matrices. While N-H bending and stretching vibrations play major roles in the SERS phenomenon of 6MP on gold surfaces in neutral solution, the strongest enhancement in acidic environment is mostly due to an Au⋅⋅⋅H-S coupling, rather than an aromatic ring-gold surface π overlap as previously proposed.

Application of Raman Spectroscopic Methods in Food Safety: A Review

Food detection technologies play a vital role in ensuring food safety in the supply chains. Conventional food detection methods for biological, chemical, and physical contaminants are labor-intensive, expensive, time-consuming, and often alter the food samples. These limitations drive the need of the food industry for developing more practical food detection tools that can detect contaminants of all three classes. Raman spectroscopy can offer widespread food safety assessment in a non-destructive, ease-to-operate, sensitive, and rapid manner. Recent advances of Raman spectroscopic methods further improve the detection capabilities of food contaminants, which largely boosts its applications in food safety. In this review, we introduce the basic principles of Raman spectroscopy, surface-enhanced Raman spectroscopy (SERS), and micro-Raman spectroscopy and imaging; summarize the recent progress to detect biological, chemical, and physical hazards in foods; and discuss the limitations and future perspectives of Raman spectroscopic methods for food safety surveillance. This review is aimed to emphasize potential opportunities for applying Raman spectroscopic methods as a promising technique for food safety detection.

Rapid and ultrasensitive detection of food contaminants using surface-enhanced Raman spectroscopy-based methods

With the globalization of food and its complicated networking system, a wide range of food contaminants is introduced into the food system which may happen accidentally, intentionally, or naturally. This situation has made food safety a critical global concern nowadays and urged the need for effective technologies capable of dealing with the detection of food contaminants as efficiently as possible. Hence, Surface-enhanced Raman spectroscopy (SERS) has been taken as one of the primary choices for this case, due to its extremely high sensitivity, rapidity, and fingerprinting interpretation capabilities which account for its competency to detect a molecule up to a single level. Here in this paper, we present a comprehensive review of various SERS-based novel approaches applied for direct and indirect detection of single and multiple chemical and microbial contaminants in food, food products as well as water. The aim of this paper is to arouse the interest of researchers by addressing recent SERS-based, novel achievements and developments related to the investigation of hazardous chemical and microbial contaminants in edible foods and water. The target chemical and microbial contaminants are antibiotics, pesticides, food adulterants, Toxins, bacteria, and viruses. In this paper, different aspects of SERS-based reports have been addressed including synthesis and use of various forms of SERS nanostructures for the detection of a specific analyte, the coupling of SERS with other analytical tools such as chromatographic methods, combining analyte capture and recognition strategies such as molecularly imprinted polymers and aptasensor as well as using multivariate statistical analyses such as principal component analysis (PCA)to distinguish between results. In addition, we also report some strengths and limitations of SERS as well as future viewpoints concerning its application in food safety.

Electrokinetically-Driven Assembly of Gold Colloids into Nanostructures for Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) enables the highly sensitive detection of (bio)chemical analytes in fluid samples; however, its application requires nanostructured gold/silver substrates, which presents a significant technical challenge. Here, we develop and apply a novel method for producing gold nanostructures for SERS application via the alternating current (AC) electrokinetic assembly of gold nanoparticles into two intricate and frequency-dependent structures: (1) nanowires, and (2) branched "nanotrees", that create extended sensing surfaces. We find that the growth of these nanostructures depends strongly on the parameters of the applied AC electric field (frequency and voltage) and ionic composition, specifically the electrical conductivity of the fluid. We demonstrate the sensing capabilities of these gold nanostructures via the chemical detection of rhodamine 6G, a Raman dye, and thiram, a toxic pesticide. Finally, we demonstrate how these SERS-active nanostructures can also be used as a concentration amplification device that can electrokinetically attract and specifically capture an analyte (here, streptavidin) onto the detection site.

4-Mercaptobenzoic Acid Labeled Gold-Silver-Alloy-Embedded Silica Nanoparticles as an Internal Standard Containing Nanostructures for Sensitive Quantitative Thiram Detection

In this study, SiO2@Au@4-MBA@Ag (4-mercaptobenzoic acid labeled gold-silver-alloy-embedded silica nanoparticles) nanomaterials were investigated for the detection of thiram, a pesticide. First, the presence of Au@4-MBA@Ag alloys on the surface of SiO2 was confirmed by the broad bands of ultraviolet-visible spectra in the range of 320-800 nm. The effect of the 4-MBA (4-mercaptobenzoic acid) concentration on the Ag shell deposition and its intrinsic SERS (surface-enhanced Raman scattering) signal was also studied. Ag shells were well coated on SiO2@Au@4-MBA in the range of 1-1000 µM. The SERS intensity of thiram-incubated SiO2@Au@4-MBA@Ag achieved the highest value by incubation with 500 µL thiram for 30 min, and SERS was measured at 200 µg/mL SiO2@Au@4-MBA@Ag. Finally, the SERS intensity of thiram at 560 cm-1 increased proportionally with the increase in thiram concentration in the range of 240-2400 ppb, with a limit of detection (LOD) of 72 ppb.

Detection of Permethrin pesticide using silver nano-dendrites SERS on optical fibre fabricated by laser-assisted photochemical method

Permethrin, 3-Phenoxybenzyl (1 RS)-cis,trans-3-(2,2-dichlorovinyl)- 2,2-dimethylcyclopropanecarboxylate, has a wide range of applications like insecticide, insect repellent and prevents mosquito-borne diseases, such as dengue fever and malaria in tropical areas. In this work, we develop a prominent monitoring method for the detection of permethrin pesticide using surface-enhanced Raman scattering (SERS) optical fibre substrates. The novel SERS-active optical fibre substrates were grown and deposited silver (Ag) nano-dendrites on the end of multi-mode fibre core by laser-assisted photochemical method. The characteristic of the Ag-nanostructures could be controlled by the experimental conditions, namely, laser illumination time. Ag nanoparticles optical fibre substrates and Ag nano-dendrites optical fibre substrates were prepared with laser illumination time of 3 min and 8 min, respectively. The achieved SERS-activity optical fibre substrates were tested with Rhodamine 6G aqueous solutions. We demonstrate that the SERS activity coupled with Ag nano-dendrites optical fibre substrate has higher Raman enhancement factor due to the creation of many of hot-spots for amplifying Raman signals. Besides, the stability and reproducibility of the Ag nano-dendrites optical fibre substrate were also evaluated with stored time of 1000 hours and relative standard deviation of less than 3%. The Ag nano-dendrite optical fibre substrate was selected for detection of permethrin pesticide in the concentration range of 0.1 ppm-20 ppm with limit of quantification (LOQ) of 0.1 ppm and calculated limit of detection (LOD) of 0.0035 ppm, proving its great potential for direct, rapid detection and monitoring of permethrin.

Surface-Enhanced Raman Scattering Detection of Fipronil Pesticide Adsorbed on Silver Nanoparticles

This work presents a surface-enhanced Raman scattering (SERS) and density functional theory (DFT) study of a fipronil adsorbed on colloidal silver nanoparticles (AgNPs). A standard curve was established to quantify fipronil within a range of 0.0001⁻0.1 ppm (r² ≥ 0.985), relying on the unique fipronil Raman shift at ~2236 cm^-1 adsorbed on AgNPs. DFT calculations suggest that the nitrile moiety (C≡N) binding should be slightly more favorable, by 1.92 kcal/mol, than those of the nitrogen atom of the pyrazole in fipronil and Ag₆ atom clusters. The characteristic peaks of the SERS spectrum were identified, and both the calculated vibrational wavenumbers and the Raman intensity pattern were considered. The vibrational spectra of fipronil were obtained from the potential energy distribution (PED) analysis and selective Raman band enhancement.

Nanomaterials based optical and electrochemical sensing of histamine: Progress and perspectives

Histamine is known to be a principal causative agent associated with marine food poisoning outbreaks worldwide, which is typically formed in the contaminated food by decarboxylation of histidine by bacterial histidine decarboxylase. Upon quantification of histamine in different food products, one can comment on the quality of the food and use it as an indicator of the good manufacturing practices and the state of preservation. The United States Food and Drug Administration (FDA) has established 50 ppm (50 mg/kg) of histamine as the chemical index for fish spoilage. Consumption of foods containing histamine higher than the permissible limit can cause serious health issues. Several methods have been developed for the determination of histamine in a variety of food products. The conventional methods for histamine detection such as thin layer chromatography, capillary zone electrophoresis, gas chromatography, colorimetry, fluorimetry, ion mobility spectrometry, high-performance liquid chromatography, and enzyme-linked immunosorbent assay (ELISA), are being used for sensitive and selective detection of histamine. However, there are a number of disadvantages associated with the conventional techniques, such as multi-step sample processing and requirement of expensive sophisticated instruments, which restrict their applications at laboratory level only. In order to address the limitations associated with the traditional methods, new approaches have been developed by various research groups. Current advances in nanomaterial-based sensing of histamine in different food products have shown significant measurement accuracy due to their high sensitivity, specificity, field deployability, cost and ease of operation. In this review, we have discussed the development of nanomaterials-based histamine sensing assays/strategies where the detection is based on optical (fluorescence, surface enhanced Raman spectroscopy (SERS), localized surface plasmon resonance) and electrochemical (impedimetric, voltammetry, potentiometric, etc.). Further, the advantages, disadvantages and future scope of the nanomaterials-based histamine sensor research are highlighted.