In Situ Recyclable Surface-Enhanced Raman Scattering-Based Detection of Multicomponent Pesticide Residues on Fruits and Vegetables by the Flower-like MoS2@Ag Hybrid Substrate

Ultrasensitive detection of contaminants in milk using a novel NMS-Ag modified water-resistant paper substrate

Rapid and precise detection of harmful substances in food products is essential for ensuring public health and safety. This study introduces a novel surface-enhanced Raman spectroscopy (SERS) substrate, composed of a molybdenum disulfide‑silver nanocomposite, applied to flexible, water-resistant filter paper for detecting melamine and bisphenol A (BPA) in milk. Optimized molybdenum disulfide (NMS) nanoflowers (NFs) were synthesized through hydrothermal methods and high-temperature annealing, then modified with silver (Ag) nanoparticles to form the NMS-Ag nanocomposite (NMSA6). This substrate greatly enhances the Raman signal, achieving an enhancement factor of approximately 1.49 × 107 and a detection limit as low as 10-11 M for simultaneous multi-component analysis. Finite-difference time-domain (FDTD) simulations confirm the enhancement mechanism. The NMSA6 substrate demonstrates remarkably low detection limits for BPA and melamine, facilitating the analysis of various hazardous substances. These findings highlight the substrate's potential for highly sensitive, label-free detection, presenting a viable tool for food safety monitoring.

Bifunctional MoO3-x/CuS Heterojunction Nanozyme-Driven "Turn-On" SERS Signal for the Sensitive Detection of Cerebral Infarction Biomarker S100B

The use of nanozymes has become a promising auxiliary approach to "turn on" surface-enhanced Raman scattering (SERS) signals for the label-free detection of disease markers. Nevertheless, there are still major challenges to develop bifunctional nanomaterials with both excellent enzyme-like activity and high SERS performance. To this end, a novel Z-scheme MoO3-x/CuS heterojunction was first constructed as a powerful "two-in-one" substrate, which can not only catalyze leucomalachite green (LMG) to SERS-active malachite green (MG) but also serve as an efficient substrate to amplify the SERS signal of catalysate. Due to the strong interfacial coupling effect between the MoO3-x and CuS nanomaterial, which promoted the separation and transport of carriers in the heterojunction, the MoO3-x/CuS heterojunction showed higher peroxidase-like activity compared to individual components and the previously reported heterojunction nanozymes. Inspired by these results, a sandwich-type SERS immunoassay for the detection of the cerebral infarction biomarker S100 calcium-binding protein (S100B) was proposed based on the output signal of MG at 1620 cm-1. Furthermore, introducing the antifouling material chitosan on the surface of the MoO3-x/CuS heterojunction can effectively resist nonspecific protein adsorption and significantly improve the detection accuracy of the immunoassay. Therefore, the SERS immunoassay based on the MoO3-x/CuS heterojunction realized highly sensitive and selective detection of S100B in the concentration range of 0.001 to 100 ng/mL, with a low limit of detection of 0.47 pg/mL. The developed method has been successfully used for the accurate detection of S100B in clinical serum. The results showed that the level of S100B in the serum of cerebral infarction patients can be distinguished from those of healthy individuals and intracranial tumor patient controls. In addition, the acquired values of S100B in the serum of cerebral infarction patients based this strategy were well consistent with the results of electrochemiluminescence (ECL) detection with a relative error of less than ±7.3. It is expected that this work may open up a paradigm for improving detection sensitivity and accuracy for the early diagnosis and treatment monitoring of cerebral infarction in the clinic.

Non-invasive detection of systemic lupus erythematosus using SERS serum detection technology and deep learning algorithms

Systemic lupus erythematosus (SLE) is an autoimmune disease with multiple symptoms, and its rapid screening is the research focus of surface-enhanced Raman scattering (SERS) technology. In this study, gold@silver-porous silicon (Au@Ag-PSi) composite substrates were synthesized by electrochemical etching and in-situ reduction methods, which showed excellent sensitivity and accuracy in the detection of rhodamine 6G (R6G) and serum from SLE patients. SERS technology was combined with deep learning algorithms to model serum features using selected CNN, AlexNet, and RF models. 92 % accuracy was achieved in classifying SLE patients by CNN models, and the reliability of these models in accurately identifying sera was verified by ROC curve analysis. This study highlights the great potential of Au@Ag-PSi substrate in SERS detection and introduces a novel deep learning approach for SERS for accurate screening of SLE. The proposed method and composite substrate provide significant value for rapid, accurate, and noninvasive SLE screening and provide insights into SERS-based diagnostic techniques.

Superhydrophobic nanocellulose-based self-assembled flexible SERS substrates for pesticide detection

Flexible surface-enhanced Raman scattering (SERS) substrates that provide simple sampling are helpful for the on-site detection of explosive contamination, pesticide residues on food surfaces, and water pollution in public spaces. Using superhydrophobic nanocellulose-based film as the support, 2D flexible SERS substrates that integrated sampling, enrichment, and detection were successfully fabricated via the solvent-induced evaporation method. This approach enabled the co-loading of two plasmonic nanoparticles with different sizes and shapes. A uniform and dense distribution of two-dimensional "hot spots" was created by the plasmonic nanoparticles' self-assembly on the hydrophobic substrate. By adjusting the loading ratio of Au-core/Ag-shell nanocubes and gold nanospheres, their synergistic effect optimized the "hot spots" structure and significantly increased the SERS signal intensity. Additionally, the hydrophobic property of the substrate allowed the target analytes to be concentrated throughout the drying process, significantly increasing the sensitivity of SERS detection. This flexible substrate can sensitively and accurately detect the pesticide residues of phosphorus and methyl parathion on apple peel with the detection limit of 10-7 g/L and relative standard deviation (RSD) less than 10 %. The high-performance SERS substrate has great potential for in-situ detection applications such as food safety and environmental monitoring.

Advancements in reusable SERS substrates for trace analysis applications

Surface Enhanced Raman Spectroscopy (SERS) technique is an effective analytical technique in which fingerprint information about analytes can be obtained, can provide detection limit performance at the single molecule level, and analyzes are performed in a single step without any intermediate steps. SERS technique offers additional benefits rather than other analytical techniques including high selectivity, ultrasensitive detection, uncomplicated protocols, in situ sampling, on-set capability and cost-effectiveness. As a result of the combination of developments in materials and nanotechnology science with the SERS analysis technique, this technique strengthens its use advantage day by day. The most important factor that limited the use of this technique was the fact that the solution containing the desired analyte(s) was dropped onto the SERS substrate and the same substrate could not be reused in subsequent analyses. To solve this problem, scientists have focused on developing reusable SERS substrates in recent years. In these studies, scientists basically used three SERS substrate cleaning applications (1) washing the SERS substrate with a suitable solvent that can elute the analyte from SERS surface after analysis, (2) cleaning the SERS substrate with catalytic degradation of analytes after analysis by modifying them with catalytic active materials and (3) Applying plasma cleaning procedure to SERS substrate after analysis and (4) applying adsorption and desorption procedure prior to SERS analysis. Herein, the aim of this review article is to evaluate the reusable SERS substrates-based methods based on their level of development and their potential to recycle. This review offers a coherent discussion on a wide range of sensing schemes employed in fabricating the SERS substrates. We utilized a critical approach in which elaborative examples were selected to highlight key shortcomings of various experimental configurations. In the same vein, there is a discussion of the advantages and limitations concerning the key instrumental advances and the expansion of the recent methods developed in this area.

V-Shaped Heterostructure Nanocavities Array with CM and EM Coupled Enhancement for Ultra-Sensitive SERS Substrate

The field of semiconductor surface-enhanced Raman scattering (SERS) substrates has experienced significant advancements, leading to a wide range of applications in several fields. However, the quest for new ultra-sensitive semiconductor SERS materials is still of utmost importance. In this regard, an efficient and novel substrate, F4TCNQ/MoS2 heterostructure is introduced, assisted by V-shaped aluminum anodic oxide (AAO) nanocavities with different depths. Utilizing the efficient charge transfer of organic/inorganic semiconducting heterostructure and the photoconfinement capability of the nanocavity structure of the AAO nanotemplate, excellent stability, fast sensing, enhanced Raman, and photodegradation activities are achieved. Due to its unique 3D structure, the optimized F4TCNQ/MoS2/AAO with 1500 nm depth achieves ultra-high sensitivity detection of 9.0×10-16 M for conventional probe molecules. Furthermore, precise detection of water contaminants is observed for the first time with a V-shaped heterostructure due to combined organic/inorganic features that differ significantly from conventional MoS2 structures or other metal/inorganic or inorganic/inorganic semiconductors. This research presents a novel and versatile strategy for SERS and demonstrates its diverse potential performance in practical applications.

Multi-confinement structured carbon dots with long room temperature phosphorescence lifetime and efficiency for sensing thiram residues assisted by copper ions

Room temperature phosphorescent carbon dots (NCCDs@SiO2) were obtained by encapsulating hydrothermally synthesized CDs in a dense Si-O network structure after high-temperature calcination using silica as the matrix. This can avoid the quenching effect of dissolved oxygen in water and has a phosphorescence lifetime of up to 2.41 s. Using the phosphorescence property of NCCDs@SiO2, a phosphorescence quenching sensor was developed for the sensitive and selective detection of thiram with the assistance of Cu2+. Cu2+-thiram complexes led to a rapid phosphorescence quenching of NCCDs@SiO2 within 30 s through the inner filter effect. The linear range of phosphorescence for thiram was 0.5-100 µM with a detection limit of 0.121 µM. The proposed method was able to detect thiram in real samples and was validated by high-performance liquid chromatography (HPLC) confirming the potential of this phosphorescence sensing method for thiram detection. This work opens up a new avenue for the detection of thiram residues in fruits and vegetables and also provides a new idea for the design of a rapid detection platform using other room temperature phosphorescent materials.

Insights into nonlinear absorption transitions in a silver-incorporated reduced graphene oxide-molybdenum disulfide (Ag-rGO-MoS2) hybrid

Optical nonlinearity in a silver-decorated reduced graphene oxide-molybdenum disulfide (Ag-rGO-MoS2) nanocomposite was experimentally investigated via the Z-scan technique using a Q-switched Nd:YAG nanopulsed green laser. An interesting switching behaviour from saturable to reverse saturable absorption with varying input on-axis intensity of the laser was demonstrated. Under low-intensity laser excitation, Ag-rGO-MoS2 displayed ground-state bleaching, which resulted in saturable absorption (SA) behaviour. Here, the prominent SPR phenomenon of Ag enforced plasmon absorption and is assigned to the SA process. Interestingly at higher intensity, the material switched its nonlinearity to reverse saturable absorption (RSA), attributed to two different mechanisms of two-photon absorption (2PA). At moderate laser pulse energies, the sample underwent sequential 2PA, which is underpinned by calculated varying nonlinear optical parameters and excited-state absorption cross-sections. However, at higher intensities, nonlinear absorption coefficients and excited-state absorption cross-sections remained constant, indicating the occurrence of genuine 2PA. In addition, theoretical estimation of the 2PA cross-section validates the observed transition. Thus, experimental evidence for the validity of nonlinear absorption theory (intensity-dependent transition from linear to nonlinear SA to nonlinear RSA to genuine 2PA via sequential 2PA) is provided for the first time in the literature.

Electrochemiluminescence detection of diazinon in vegetables based on the synergistic interaction of WO3-x dots with Au@SiO2 nanocapsules

In this work, a simple synthesis of low-toxicity transition metal material of WO3-x dots was used as a co-reactant with Au@SiO2 as a core-shell material and a signal amplification factor to collaboratively promote Ru(bpy)32+ electrochemiluminescence (ECL) for the construction of a highly sensitive aptasensor for the detection of diazinon (DZN) in vegetables. Electrodes modified with multi-walled carbon nanotubes-chitosan composite membranes (MWCNTs-CS) were used to load and immobilize more Ru(bpy)32+.can load more Ru(bpy)32+. WO3-x dots synthesized by a simple method showed excellent ECL efficiency as a novel co-reactant for Ru(bpy)32+. Under optimized conditions, this aptasensor for DZN has a wide detection range (10 pg mL-1 - 1 μg mL-1.) and a low detection limit (0.0197 ng L-1). The aptasensor has shown good results in the analysis of real samples in the experiment. This work provides a new approach to the construction of a novel electrochemiluminescence sensor for the detection of pesticides.

Flexible, scalable and simple-fabricated silver nanorod-decorated bacterial nanocellulose SERS substrates cooperated with portable Raman spectrometer for on-site detection of pesticide residues

Owing to good flexibility, prominent mechanical properties, three-dimensional (3D) nanofibrous structure and low background interference, sustainable bacterial nanocellulose (BNC) is a highly attractive matrix material for surface-enhanced Raman scattering (SERS) sensor. Herein, a highly sensitive, flexible and scalable silver nanorod-decorated BNC (AgNRs@BNC) SERS sensor is developed by a simple vacuum-assisted filtration. The AgNRs were firmly locked in the 3D nanofibrous network of cellulose nanofibers upon vacuum drying process, resulting in the formation of 3D SERS hotspots with a depth of more than 10 μm on the sensor. With 4-aminothiophenol (4-ATP) as a target molecule, a lowest distinguishable level of 10-12 M and a high enhancement factor of 1.1 × 109 were realized by the optimal AgNRs1.5@BNC SERS sensor. Moreover, the AgNRs@BNC SERS sensor exhibits high detectable level of 10-9 M for thiram molecules by integrating with a portable Raman spectrometer. Besides, toxic thiram residues on grape surface could be directly on-site identified by the combination of AgNRs@BNC SERS sensors and a portable Raman spectrometer through a feasible press-and-peel method. The flexible AgNRs@BNC SERS sensor cooperated with portable Raman system demonstrates great potential for on-site detection of pesticide residues on irregular food surfaces.

SERS imaging investigation of the removal efficiency of pesticide on vegetable leaves by using different surfactants

Pesticide residues on vegetables could be removed by commercial detergents to guarantee food safety, but the removal efficiencies of different formulations of detergents need to be further investigated. In this work, surface enhanced Raman scattering (SERS) imaging method due to its good space resolution as well as high sensitivity is used to track the thiram residue, and evaluate the pesticide removing efficiencies by mixtures of several surfactants at different ratios. Sodium linear alkylbenzene sulphonate-alkyl glycoside (LAS-APG) with the ratio at 5:5 and the concentration at 0.2 % show the best removing effect. In addition, HPLC method is employed to validate the results of SERS imaging. Furthermore, LAS-APG mixture could be efficiently washed out from the leaves through simple household cleaning, meaning no secondary contamination. It is perspective that SERS imaging is an effective technique to explore the effect of fruit and vegetable detergents in removing pesticide residues.

Current and emerging nanotechnology for sustainable development of agriculture: Implementation design strategy and application

Recently, agriculture systems have faced numerous challenges involving sustainable nutrient use efficiency and feeding, environmental pollution especially heavy metals (HMs), infection of harmful microorganisms, and maintenance of crop production quality during postharvesting and packaging. Nanotechnology and nanomaterials have emerged as powerful tools in agriculture applications that provide alternatives or support traditional methods. This review aims to address and highlight the current overarching issue and various implementation strategies of nanotechnology for sustainable agriculture development. In particular, the current progress of different nano-fertilizers (NFs) systems was analyzed to show their advances in enhancing the uptake and translocations in plants and improving nutrient bioavailability in soil. Also, the design strategy and application of nanotechnology for rapid detection of HMs and pathogenic diseases in plant crops were emphasized. The engineered nanomaterials have great potential for biosensors with high sensitivity and selectivity, high signal throughput, and reproducibility through various detection approaches such as Raman, colorimetric, biological, chemical, and electrical sensors. We obtain that the development of microfluidic and lab-on-a-chip (LoC) technologies offers the opportunity to create on-site portable and smart biodevices and chips for real-time monitoring of plant diseases. The last part of this work is a brief introduction to trends in nanotechnology for harvesting and packaging to provide insights into the overall applications of nanotechnology for crop production quality. This review provides the current advent of nanotechnology in agriculture, which is essential for further studies examining novel applications for sustainable agriculture.

High performance and recyclable Ag/ZnO/PM substrate for the detection of organic pollutants

A sensitive and recyclable substrate was fabricated through in situ reduction of silver nanoparticles (NPs) on zinc oxide nanorods (NRs). The prepared silver nanoparticles/zinc oxide nanorods/polyamide mesh (Ag/ZnO/PM) substrate exhibited not only excellent surface-enhanced Raman scattering (SERS) performance to R6G with a limit of detection (LOD) of 10-12 M, mainly attributed to the synergistic effect of the suitable size and the nanoscale gaps of the Ag NPs to produce local surface plasmon resonance (LSPR), but also outstanding self-cleaning property via UV irradiation due to its significant photocatalytic property based on the non-equilibrium carriers generated by ZnO and the presence of Schottky junctions between Ag and ZnO. The substrate showed good recycling stability even after five cycles. Furthermore, the successful recyclable application of Ag/ZnO/PM for tetracycline hydrochloride (TC) detection with high sensitivity further suggested that it is a promising candidate for constructing a portable SERS platform to detect organic pollutants.

2D TiS2-Nanosheet-Coated Concave Gold Arrays with Triple-Coupled Resonances as Sensitive SERS Substrates

Herein, a hybrid substrate for surface-enhanced Raman scattering (SERS) is fabricated, which couples localized surface plasmon resonance (LSPR), charge transfer (CT) resonance, and molecular resonance. Exfoliated 2D TiS2 nanosheets with semimetallic properties accelerate the CT with the tested analytes, inducing a remarkable chemical mechanism enhancement. In addition, the LSPR effect is coupled with a concave gold array located underneath the thin TiS2 nanosheet, providing a strong electromagnetic enhancement. The concave gold array is prepared by etching silicone nanospheres assembled on larger polystyrene nanospheres, followed by depositing a gold layer. The LSPR intensity near the gold layer can be adjusted by changing the layer thickness to couple the molecular and CT resonances, in order to maximize the SERS enhancement. The best SERS performance is recorded on TiS2-nanosheet-coated plasmonic substrates, with a detectable methylene blue concentration down to 10-13 m and an enhancement factor of 2.1 × 109 and this concentration is several orders of magnitude lower than that of the TiS2 nanosheet (10-11 m) and plasmonic substrates (10-9 m). The present hybrid substrate with triple-coupled resonance further shows significant advantages in the label-free monitoring of curcumin (a widely applied drug for treating multiple cancers and inflammations) in serum and urine.

A robust electrochemical sensor based on AgNWs@MoS2 for highly sensitive detection of thiabendazole residues in food samples

Thiabendazole (TBZ), a highly toxic phosphorothioate insecticide commonly used in postharvest fruit management, has the potential to cause detrimental effects on human health as an endocrine disruptor. In this study, an electrochemical sensor was developed to detect TBZ by modifying MoS2 on silver nanowires (Ag NWs@MoS2) and integrating them onto a glassy carbon surface. Cyclic voltammetry revealed that TBZ underwent an irreversible, diffusion-controlled process on Ag NWs@MoS2, leading to a two-fold increase in peak current compared to unmodified MoS2. Square wave voltammetry facilitated TBZ detection, and the sensor exhibited a linear range of 0.05-10 μM with a high coefficient of determination (R2 = 0.9958) and a limit of detection (LOD) of 1.75 nM (signal-to-noise ratio = 3). The sensor's applicability for food safety monitoring was verified through TBZ analysis in pear and apple samples, achieving recoveries of 95.5-103.6% with RSDs in the range of 1.98-3.25%.

Photochemical decoration of gold nanoparticles on MoS2 nanoflowers grafted onto the flexible carbon cloth as a recyclable SERS sensor for the detection of antibiotic residues on curved surfaces

Surface-enhanced Raman spectroscopy (SERS)-based flexible substrate has recently been demonstrated to be effective in detecting molecules on curved surfaces, however a suitable method for fabricating the flexible SERS substrate still remains a hurdle. In this paper, we fabricated a flexible SERS substrate by anchoring the plasmonic gold nanoparticles (Au-NPs) onto the hydrothermally grown flower-like molybdenum disulfide (MoS2) grafted onto carbon cloth (CC) via a facile photoreduction route. Benefitting from the abundant hotspots generation of the Au-NPs and photo-induced charge-transfer ability of MoS2, the constructed Au-NPs/MoS2/CC substrate exhibit a superior SERS sensing ability, excellent SERS enhancement factor, high flexibility and mechanical stability towards the nitrofurantoin (NFT) with an ultra-low detection limit of 10-11 M. As a trial for practical applications, the flexible substrate was used to detect NFT (10-4 M) in the curved surfaces of meat samples via swab technique. The ability of the flexible Au-NPs/MoS2/CC substrate to sustain the robust Raman signals of NFT even after recycling up to 4 cycles validated its reusability. The proposed flexible SERS substrate with reusable capability indicates its great potential in practical applications for the detection of target molecules on the curved surfaces.

Multifunctional Ni(OH)2/Ag composites for ultrasensitive SERS detection and efficient photocatalytic degradation of ciprofloxacin and methylene blue

To enable the widespread application of surface-enhanced Raman scattering (SERS) technique in practical sensing of organic pollutants, it is essential to develop a reliable SERS substrate that offers both high sensitivity and reusability. In this study, we employed a simple and rapid in-situ deposition method to coat Ag nanoparticles onto flower-like Ni(OH)2 spheres, resulting in the formation of Ni(OH)2/Ag composites with excellent photocatalytic performance and SERS activity. These composites were used as a promising SERS analysis tool for effective detection of organic pollutants, including ciprofloxacin hydrochloride (CIP) and methylene blue (MB). Notably, the composites exhibited outstanding detection limits of 10-8 M for MB and 10-7 M for CIP, respectively, and showed a strong linear relationship between SERS intensities and the logarithmic concentration (R2 ≥ 0.97). Moreover, under simulated sunlight irradiation, the Ni(OH)2/Ag composites efficiently degraded MB and CIP molecules within a short period of 120 min for MB and 130 min for CIP. This demonstrated their practical reusability, as evidenced by their consistent performance over five cycles of SERS sensing. These findings underscore the significant potential of these composites for SERS-based detection of trace pollutants and ecological restoration through photocatalytic reactions in the future.

Sludge biodrying coupled with photocatalysis improves the degradation of extracellular polymeric substances

The efficiency of sludge dewatering is limited by extracellular polymeric substances (EPS) during biodrying. This study investigated the effect of photocatalysis-mediated EPS degradation on sludge dewatering performance during the sludge biodrying process. The photocatalysis of municipal sludge was first carried out to choose a cost-efficient catalyst. Then sludge biodrying tests were performed using TiO2-coated amendment (TCA) and uncoated amendment (TUCA) as the control. Municipal sludge photocatalysis results showed that using TiO2 could efficiently degrade carbohydrates and proteins in the EPS within 60 min. After 20-day biodrying, photocatalysis significantly promoted a reduction in the moisture content and EPS by 17.64% and 6.88%, respectively. The surface-enhanced Raman scattering (SERS) intensities of the C-C-O symmetric stretching vibration peak of D-lactose and the C-S stretching vibration peak of cysteine were significantly decreased by approximately 33.19% and 44.76%, respectively, indicating that photocatalysis indeed promoted the reduction of polysaccharides and cysteine in the EPS, especially after the thermophilic phase. The hydrophilic amino acid content decreased by 23.02%, verifying that photocatalysis could improve EPS hydrophobicity. Consequently, municipal sludge biodrying coupled with photocatalysis promotes sludge EPS degradation and enhances sludge dewaterability, improving the efficiency of sludge biodrying.

Ultrasensitive SERS-based detection of prostate cancer exosome using Cu2O-CuO@Ag composite nanowires

Exosome is a recently emerging cancer-associated biomarker for early diagnostic and prognostic owing to their noninvasive, intrinsic stability, and representativeness of primitive cell state. However, the development of convenient and quantitative methods for exosome analysis remains technically challenging. Here, we proposed a cost-effective assay for the direct capture and rapid monitoring of exosomes utilizing the multifunctional surface enhanced Raman scattering (SERS) substrate, which consisted of Cu2O-CuO nanowires prepared by a simple thermo-oxidative growth method and subsequently sputtered with Ag NPs. This reticulate substrate made up of interlaced one-dimensional nanowires that highly favored for exosome recognition and collection. Particularly, the electromagnetic hotspots with high density were uniformly distributed on the nanowires due to uniform physical deposition, facilitating robust SERS property with an enhancement factor (EF) of 3.3 × 108 and signal reproducibility with a relative standard deviation (RSD) of 13%. In addition, the presence of Cu2O-CuO heterojunction enabled further elevation of the SERS performance attributed to the effective charge transfer, triggering a significant chemical enhancement effect. Finally, clinical validation with the serum specimens of prostate cancer patients indicated that the proposed immunosensor possessed great potential for application in rapid cancer screening and diagnosis.

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.

Efficient interfacial self-assembled MXene/Ag NPs film nanocarriers for SERS-traceable drug delivery

Combining the unique advantages of two-dimensional transition metal carbon/nitrogen compounds (MXene) and the excellent surface-enhanced Raman scattering (SERS) performance of noble metal materials, MXene/Ag NPs films were proposed as nanocarriers for SERS-traceable drug delivery. The films were prepared by two-step self-assembly on positively charged silicon wafers using virtue of the high evaporation of ethyl acetate, the Marangoni effect, and an oil/water/oil three-phase system. With 4-mercaptobenzoic acid (4-MBA) as the probe molecule, the SERS detection limit was 10-8 M and had shown a good linear relationship in the range of 10-8-10-3 M. Simultaneously, the film had good uniformity, repeatability, and stability. When Ti3C2Tx/Ag NPs films were used as nanocarriers, the anticancer drug doxorubicin (DOX) was loaded onto the surface through 4-MBA, and the tracking and monitoring were realized by SERS. The addition of glutathione (GSH) triggered the thiol exchange reaction, resulting in the shedding of 4-MBA from the surface of the film, which indirectly achieved the efficient release of DOX. Furthermore, the loading of DOX and the drug release effect triggered by GSH maintained a certain stability in serum, which provided a potential possibility for the subsequent loading and release of drugs by films with three-dimensional structures as scaffolds in biological therapy. Self-assembled MXene/Ag NPs film nanocarriers for SERS-traceable drug delivery and GSH-triggered high-efficiency drug release.

Sensing of organophosphorus pesticides by fluorescent complexes based on purine-hydrazone receptor and copper (II) and its application in living-cells imaging

In this study, we used purine hydrazone derivatives and coumarin aldehyde to synthesize a novel fluorescent sensor (EDTP) by Schiff base reaction, which exhibited significant selective fluorescence quenching of Cu²⁺, and a distinct change from brilliant yellow to red is present along with the solution color. The detection limit of EDTP for Cu²⁺ was 109.52 nM. Job's plot experiment, density flooding theory (DFT) and ¹H NMR titration experiments revealed the possible binding mechanism of EDTP to Cu²⁺, the probe EDTP could achieve highly detection of Cu²⁺ through forming a 1:1 complex. Additionally, this new fluorescent sensor EDTP-Cu²⁺ can be further applied in the rapid and selective detection of pesticide residues in solutions. When the EDTP-Cu²⁺ system was subsequently exposed to organophosphorus pesticides (glyphosate and glufosinate-ammonium), it was observed that the fluorescence was recovered and accompanied by a red to yellow color change. This may be attributed to the strong chelation of glyphosate and glufosinate-ammonium with Cu²⁺, leading to the dissociation of the EDTP-Cu²⁺ system and thus triggering the fluorescence recovery effect. The detection limits of the EDTP-Cu²⁺ system is 2.48 nM for glyphosate and 17.23 nM for glufosinate-ammonium, respectively. Finally, the developed sensor system has been successfully utilized image glyphosate and glufosinate-ammonium fluorescence in living cells. Purine fluorescence probes are a potential fluorescent probe for the detection of metal ions and pesticides due to their good characteristics. This study opens up a new way for the detection of fluorescent probes in pesticides.

Pesticide Residue Fast Screening Using Thermal Desorption Multi-Scheme Chemical Ionization Mass Spectrometry (TD-MION MS) with Selective Chemical Ionization

In this work, the detection characteristics of a large group of common pesticides were investigated using a multi-scheme chemical ionization inlet (MION) with a thermal desorption unit (Karsa Ltd.) connected to an Orbitrap (Velos Pro, Thermo Fisher Scientific) mass spectrometer. Standard pesticide mixtures, fruit extracts, untreated fruit juice, and whole fruit samples were inspected. The pesticide mixtures contained 1 ng of each individual target. Altogether, 115 pesticides were detected, with a set of different reagents (i.e., dibromomethane, acetonylacetone, and water) in different polarity modes. The measurement methodology presented was developed to minimize the common bottlenecks originating from sample pretreatments and nonetheless was able to retrieve 92% of the most common pesticides regularly analyzed with standardized UHPLC-MSMS (ultra-high-performance liquid chromatography with tandem mass spectrometry) procedures. The fraction of detected targets of two standard pesticide mixtures generally quantified by GC-MSMS (gas chromatography with tandem mass spectrometry) methodology was much less, equaling 45 and 34%. The pineapple swabbing experiment led to the detection of fludioxonil and diazinon below their respective maximum residue levels (MRLs), whereas measurements of untreated pineapple juice and other fruit extracts led to retrieval of dimethomorph, dinotefuran, imazalil, azoxystrobin, thiabendazole, fludioxonil, and diazinon, also below their MRL. The potential for mutual detection was investigated by mixing two standard solutions and by spiking an extract of fruit with a pesticide's solution, and subsequently, individual compounds were simultaneously detected. For a selected subgroup of compounds, the bromide (Br^-) chemical ionization characteristics were further inspected using quantum chemical computations to illustrate the structural features leading to their sensitive detection. Importantly, pesticides could be detected in actual extract and fruit samples, which demonstrates the potential of our fast screening method.

Spontaneous Redox-Reaction-Driven Growth of Ag Nanoparticles on Co(OH)2 Nanoflower Arrays for Surface-Enhanced Raman Scattering

A simple and reliable method is developed to fabricate Ag-nanoparticle-decorated Co(OH)₂ nanoflowers grafted on polyacrylonitrile (PAN) nanopillar arrays as uniform and sensitive surface-enhanced Raman scattering (SERS) substrates. First, Co(OH)₂-nanosheet-assembled nanoflowers are achieved on the highly uniform PAN nanopillar arrays via electrochemical deposition. Then, Ag nanoparticles (Ag-NPs) are decorated onto the Au-nanoparticle-precoated Co(OH)₂ nanoflowers based on a spontaneous redox reaction (SRR) between the silver ions and Co(OH)₂ nanosheets at room temperature. Ag-NPs can be successfully in situ synthesized on the Co(OH)₂ nanoflowers, and Au nanoparticles precoated on the surface of the Co(OH)₂ nanosheets can ensure that the Co(OH)₂ nanoflower structure does not collapse. Because of the highly uniform PAN nanopillar arrays and the high-density sub-10 nm gaps between the neighboring Ag-NPs on the surface of the Co(OH)₂ nanoflowers, the hierarchical three-dimensional Ag@Co(OH)_x grown on PAN nanopillar arrays can produce a reproducible and sensitive SERS effect. To verify the SERS performance of the substrate, 4-aminothiophenol (4-ATP) is used as the probe molecule, and the Ag@Co(OH)_x grown on PAN nanopillar arrays is employed as the SERS substrate. As a result, 4-ATP concentrations as low as 10^-10 M can still be identified, exhibiting high SERS activity. Additionally, the relative standard deviation value of the main characteristic peak of 10^-5 M 4-ATP is 9.43%, indicating good uniformity of the SERS signal of the substrate. The SRR between silver ions and Co(OH)₂ can provide a simple route to prepare heterostructures as SERS substrates, which has great potential for application in the field of analysis.

Au Nanoparticles Decorated CoP Nanowire Array: A Highly Sensitive, Anticorrosive, and Recyclable Surface-Enhanced Raman Scattering Substrate

Metal-semiconductor composites are promising candidates for surface-enhanced Raman scattering (SERS) substrates, but their inert basal plane, poor active sites, and limited stability hamper their commercial prospects. Herein, we report a three-dimensional CoP nanowire array decorated with Au nanoparticles on carbon cloth (Au@CoP/CC) as a self-supporting flexible SERS substrate. The Au nanoparticles spontaneously grew on the surface of the CoP nanowire array to form efficient SERS hot spots by a redox reaction with HAuCl₄ without any additional reducing agents. Such Au@CoP/CC substrate exhibited a limit of detection of 10^-11 M using rhodamine 6G as a model dye with outstanding corrosion resistance ability even under extreme acid and alkali conditions, which is better than many recently reported Au-based SERS substrates. Finite-difference time-domain simulation results demonstrated that Au@CoP/CC can provide a high density of regions with intense local electric field enhancement. Moreover, Au@CoP/CC can degrade target organic dyes for the self-cleaning and reproduction of SERS-active substrates under visible light irradiation. This work provides a novel means of using the plasmonic metal-transition metal phosphide composites for high-performance SERS sensing and photodegradation.

Fiber Optic SERS Sensor with Silver Nanocubes Attached Based on Evanescent Wave for Detecting Pesticide Residues

Surface-enhanced Raman scattering (SERS) has great potential in the field of rapid detection of pesticide residues in food. In this paper, a fiber optic SERS sensor excited by evanescent waves was proposed for efficient detection of thiram. Silver nanocubes (Ag NCs) were prepared as SERS active substrates, which had much stronger electromagnetic field intensity than nanospheres under laser excitation due to much more "hot spots". By using the method of electrostatic adsorption and laser induction, Ag NCs were uniformly assembled at the fiber taper waist (FTW) for enhancing the Raman signal. Different from the traditional way of stimulation, evanescent wave excitation greatly increased the interaction area between the excitation and analyte, while reducing the damage of the excited light to the metal nanostructures. The methods proposed in this work have been successfully used to detect the pesticide residues of thiram and showed good detection performance. The detection limits for 4-Mercaptobenzoic acid (4-MBA) and thiram were determined to be 10^-9 and 10^-8 M, the corresponding enhancement factor could be 1.64 × 10⁵ and 6.38 × 10⁴. Low concentration of thiram was detected in the peels of tomatoes and cucumbers, indicating its feasibility in actual sample detection. The combination of evanescent waves and SERS provides a new direction for the application of SERS sensors, which had great application potential in the field of pesticide residue detection.

Non-uniform droplet deposition on femtosecond laser patterned superhydrophobic/superhydrophilic SERS substrates for high-sensitive detection

Surface-enhanced Raman scattering (SERS) sensors combined with superhydrophobic/superhydrophilic (SH/SHL) surfaces have shown the ability to detect ultra-low concentrations. In this study, femtosecond laser fabricated hybrid SH/SHL surfaces with designed patterns are successfully applied to improve the SERS performances. The shape of SHL patterns can be regulated to determine the droplet evaporation process and deposition characteristics. The experimental results show that the uneven droplet evaporation along the edges of non-circular SHL patterns facilitates the enrichment of analyte molecules, thereby enhancing the SERS performance. The highly identifiable corners of SHL patterns are beneficial for capturing the enrichment area during Raman tests. The optimized 3-pointed star SH/SHL SERS substrate shows a detection limit concentration as low as 10^-15 M by using only 5 µL R6G solutions, corresponding to an enhancement factor of 9.73 × 10¹¹. Meanwhile, a relative standard deviation of 8.20% can be achieved at a concentration of 10^-7 M. The research results suggest that the SH/SHL surfaces with designed patterns could be a practical approach in ultratrace molecular detections.

Ag NC and Ag NP/PorC Film-Based Surface-Enhanced Raman Spectroscopy-Type Immunoassay for Ultrasensitive Prostate-Specific Antigen Detection

Surface-enhanced Raman scattering (SERS) is a spectral detection technology with high sensitivity and detectivity and can be used to detect the fingerprint information of the molecules with ultralow concentration. Herein, a kind of immunostructure constructed by Ag nanoparticle/porous carbon (Ag NP/PorC) films as the immunosubstrate and Ag NCs as the immunoprobes was presented for ultralow level prostate-specific antigen (PSA) detection. Experimentally, the Ag NP/PorC film was first prepared with a facile method by carbonizing the gelatin-AgNO₃ film in air, and Ag NCs were synthesized by the hydrothermal method. Then, the Ag NP/PorC film was modified by PSA antibodies as the substrate, while Ag NCs were decorated by R6G and PSA antibodies for probes. The sandwiched SERS detection embodiment was constructed by the immunoreaction between the PSA and PSA antibody predecorated on the substrate and probes. Our results show that the proposed SERS-type immunoassay is highly sensitive and selective to a wide range of PSA concentrations from 10^-5 to 10^-12 g/mL. Thereafter, it was also implemented to detect the PSA level in human serum, and the results successfully reproduce the PSA levels as those measured by the chemiluminescence method with a recovery rate above 90%. All in all, this SERS-type immunoassay provides a promising method for the early diagnosis of prostate cancer.

Nonmetallic SERS-based biosensor for ultrasensitive and reproducible immunoassay of ferritin mediated by magnetic molybdenum disulfide nanoflowers and black phosphorus nanosheets

To improve the curability of cancer patients, it is essential to propose an early diagnosis technology with ultra-high sensitivity and reliable biocompatibility. Herein, a sophisticated nonmetallic SERS-based immunosensor, comprised by a MoS₂ @Fe₃O₄ nanoflower-based immunoprobe with magnetism and a black phosphorus (BP) nanosheet-based immunosubstrate, was proposed for the specific in-situ monitoring of ferritin (FER). The sandwich immunosensor was endowed with an excellent SERS performance mainly ascribed to a synergistic chemical enhancement as well as an additional electrostatic adsorption effect, achieving a limit of detection down to 7.3 × 10^-5 μg/mL. Particularly, all the Raman label, target FER, and anti-FER could be completely degraded within 70 min under visible light irradiation owing to the favorable photocatalytic activities of MoS₂ and BP which could be then effectively separated and collected with the assistance of an external magnet. Such a recyclable nonmetallic immunosensor holds great potential and practicality in the clinical screening of cancer.

Rapid and Robust Analysis of Coumatetralyl in Environmental Water and Human Urine Using a Portable Raman Spectrometer

The widespread use and exposure of coumatetralyl (CMTT) has led to its accumulation in the environment and organisms, causing damage to ecosystems and adverse health effects in humans. Unfortunately, achieving fast detection of CMTT remains challenging. Herein, a rapid and robust surface-enhanced Raman spectroscopy (SERS) method was developed for rapid on-site detection of CMTT in environmental water and human urine. Clear trends were observed between the signal intensity and the logarithmic concentration of CMTT, ranging from 0.025 to 5.0 μg/mL with high reproducibility. The detection limits in water and human urine were as low as 1.53 and 13.71 ng/mL, respectively. The recoveries of CMTT for environmental water and urine samples were 90.2-98.2 and 82.0-87.5%, respectively, satisfactory for practical applications. The quantitative results of this approach were highly comparable to those obtained by high-performance liquid chromatography. Most importantly, it is cost-effective, operationally simple, and without a complicated sample preparation step. Detecting CMTT in water samples took only 5 min, and the detection of urine samples was completed within 8 min. This simple yet practical SERS approach offers a reliable application prospect for on-site CMTT detection in environmental water and point-of-care monitoring of poisoned patients.

ZnO nanorods decorated with Ag nanoflowers as a recyclable SERS substrate for rapid detection of pesticide residue in multiple-scenes

Pesticide residues threaten the ecological environment and human health. Therefore, developing high performance SERS substrate to achieve highly sensitive detection of pesticide residues is meaningful. In this study, based on the strategy of combining "hot spots" engineering and material hybridization, we construct a novel hybrid SERS substrate by depositing Ag nanoflowers (NFs) on ZnO nanorods (NRs). Benefiting from the synergistic effect of electromagnetic enhancement and charge transfer effect, the Ag NFs@ZnO NRs substrate exhibits a low detection limit (10^-13 M) for crystal violet molecules. This SERS substrate has good uniformity with a relative standard deviation of 7.463 %. Besides, owning to the photocatalytic property of ZnO NRs, the hybrid substrate can degrade probe molecules after SERS detection and realize recyclability. As a demonstration, we employed our SERS substrate for the trace detection of pesticide residues on apple surface and in river water. This study provides a new idea for improving the SERS performance of hybrid substrates.

Raman spectroscopy: Principles and recent applications in food safety

Food contaminant is a significant issue because of the adverse effects on human health and economy. Traditional detection methods such as liquid chromatography-mass spectroscopy for detecting food contaminants are expensive and time-consuming, and require highly-trained personnel and complicated sample pretreatment. Raman spectroscopy is an advanced analytical technique in a manner of non-destructive, rapid, cost-effective, and ultrasensitive sensing various hazards in agri-foods. In this chapter, we summarized the principle of Raman spectroscopy and surface enhanced Raman spectroscopy, the methods to process Raman spectra, the recent applications of Raman/SERS (surface-enhanced Raman spectroscopy) in detecting chemical contaminants (e.g., pesticides, antibiotics, mycotoxins, heavy metals, and food adulterants) and microbiological hazards (e.g., Salmonella, Campylobacter, Shiga toxigenic E. coli, Listeria, and Staphylococcus aureus) in foods.

An adhesive SERS substrate based on a stretched silver nanowire-tape for the in situ multicomponent analysis of pesticide residues

Two essential factors in powerful surface-enhanced Raman spectroscopy analysis of trace pesticide residues are viz., high sensitivity and efficient sampling. Herein, owing to elastic properties, a stretched Ag nanowire (Ag NW)-tape under the strain of 15% formed a wrinkled structure with periodic microridges and microgrooves, where abundant nanogaps were generated by the aggregated Ag NWs. Compared with the unstretched Ag NW-tape substrate, an appreciable signal enhancement of the modified 4-mercaptobenzoic acid (4-MBA) molecules with a ratio of 2.6 was discerned from the sophisticated SERS substrate due to the electromagnetic enhancement induced by the relatively high density of "hot spots" around the Ag NW aggregates. The as-fabricated Ag NW-tape substrate performed admirably in detecting 4-MBA and demonstrated an enhancement factor of 1.16 × 10⁶. Moreover, for the in situ detection of tetramethylthiuram disulfide, thiabendazole, and their mixture, the relatively high recovery rates of over 88% were favorably realized by the Ag NW-tape substrate with superior sensitivity, distinct flexibility, and adhesiveness. This fascinating SERS substrate, dependent on the flexible and adhesive Ag NW-tape, is promising for application in SERS analysis of trace residues on various practical surfaces.

Interface Design of 3D Flower-like Ag@ZnSe Composites: SERS and Photocatalytic Performance

In this work, we cosputtered Ag and ZnSe on a polystyrene template to form a three-dimensional (3D) Ag@ZnSe (x) structure. The 3D surface morphology and material composition that provided abundant "hot spots" were controlled by adjusting the sputtering power of the ZnSe, which was confirmed by finite-difference time-domain (FDTD) simulation. The introduction of ZnSe into the noble metal Ag also introduced a charge-transfer (CT) effect into the system, and the CT path was proven with the two-dimensional correlation spectroscopy (2D-COS)-surface-enhanced Raman scattering (SERS) technique. In addition, the substrate exhibited excellent catalytic activity due to the CT effect. The catalyzed degradation of malachite green (MG) was due to the CT effect in the system, and the catalytic process was successfully monitored by in situ SERS. Most importantly, the catalytic degradation by Ag@ZnSe (x) with different parameters was proportional to the degree of CT (ρ_CT). The SERS and catalytic mechanisms were analyzed in depth with the 2D-COS-SERS technique, which was also useful in verifying the CT process. The catalytic sites for MG were successfully monitored with the 2D-COS-SERS technique. This study provides a reference for studies of the synergistic effects of the electromagnetic mechanism and CT, as well as a new perspective on photocatalysis with dye molecules and monitoring of the catalytic processes.

Multiplex Surface-Enhanced Raman Scattering: An Emerging Tool for Multicomponent Detection of Food Contaminants

For survival and quality of human life, the search for better ways to ensure food safety is constant. However, food contaminants still threaten human health throughout the food chain. In particular, food systems are often polluted with multiple contaminants simultaneously, which can cause synergistic effects and greatly increase food toxicity. Therefore, the establishment of multiple food contaminant detection methods is significant in food safety control. The surface-enhanced Raman scattering (SERS) technique has emerged as a potent candidate for the detection of multicomponents simultaneously. The current review focuses on the SERS-based strategies in multicomponent detection, including the combination of chromatography methods, chemometrics, and microfluidic engineering with the SERS technique. Furthermore, recent applications of SERS in the detection of multiple foodborne bacteria, pesticides, veterinary drugs, food adulterants, mycotoxins and polycyclic aromatic hydrocarbons are summarized. Finally, challenges and future prospects for the SERS-based detection of multiple food contaminants are discussed to provide research orientation for further.

Facile fabrication of flexible AuNPs@CDA SERS substrate for enrichment and detection of thiram pesticide in water

Pesticide residues in water is one of the most serious problems in developing countries. Surface enhanced Raman spectroscopy (SERS) is widely used in the detection and monitoring of pesticide and other trace compounds because of its low limits of detection (LODs). However, different SERS substrate synthesis methods have different economic benefits and environmental impacts. In this paper, a flexible AuNPs@CDA SERS substrate was fabricated by the gold nanoparticles (AuNPs) and the biomass-based cellulose diacetate (CDA), which had stable test performance and considerable LODs. The substrates were economically viable and environment friendly. The characterization analysis of the substrate allows us to flexibly select different test methods (drop-test or enrichment-test) as coping strategy in different situation. The results showed that the LODs of thiram pesticide in water by enrichment-test could reach 10^-7 g/mL, and had a good linear relationship in the concentration range of 10^-7-10^-6 g/mL. This strategy can realize the rapid and effective detection and monitoring of thiram pesticide in water.

Core-shell Au@ZIF-67-based pollutant monitoring of thiram and carbendazim pesticides

A sensitive and stable substrate plays a vital role in the Raman spectroscopic techniques as an analytical method for detecting pesticides effectively from the environment. Enhancing signals from nanoparticles are weak and inconsistent in repeatability since analytes tend to degrade quickly under laser exposure. Herein, a novel substrate of Au@ZIF-67 is prepared on octahedral AuNPs by trapping pesticide molecules with small three-dimensional volumes by the flexibility of ZIF-67 for rapid detection with high sensitivity and stability. The two types of thiram and carbendazim pesticides, which are environmental pollutants that affect biodiversity, were successfully absorbed in Au@ZIF-67 nanostructures by adsorption-desorption equilibrium for analytical purposes in Raman spectroscopy. Spectra calculations of the thiram and carbendazim molecules on 8 atoms of Au using DFT were compared with the experimental data. The SERS enhancement factors for thiram and carbendazim were estimated to be 1.91 × 10⁸ and 3.12 × 10⁸, respectively, with the LOD values of trace amounts of ∼10^-10 mol L^-1. The novel substrate of Au@ZIF-67 is a propitious platform for detecting thiram and carbendazim in trace amounts, providing a helpful strategy for detecting residues with high performance in the environment at the laboratory and practical scales.

Synthesis of recyclable SERS platform based on MoS2@TiO2@Au heterojunction for photodegradation and identification of fungicides

Surface-enhanced Raman spectroscopy (SERS) substrates based on metal/semiconductors have attracted much attention due to their excellent photocatalytic activity and SERS performance. However, they generally exhibit low light utilization and photocatalytic efficiencies. Herein, molybdenum disulfide coated titanium dioxide modified with gold nanoparticles (MoS₂@TiO₂@Au) as a heterojunction-based recyclable SERS platform was fabricated for the efficient determination of fungicides. Results showed that the MoS₂@TiO₂@Au platform could rapidly degrade 90.7% crystal violet in 120 min under solar light irradiation and enable reproducible and sensitive SERS analysis of three fungicides (methylene blue, malachite green, and crystal violet) and in-situ monitor of the photodegradation process. The platform could also be reused five times due to the unique integrated merits of the MoS₂@TiO₂@Au heterojunction. Meanwhile, experiments in determining methylene blue in prawn protein solution achieved a limit of detection of 1.509 μg/L. Therefore, it is hoped that this work could expand detection applications of photocatalytic materials.

The safety of Chinese medicine: A systematic review of endogenous substances and exogenous residues

BACKGROUND

Safety and toxicity have become major challenges in the internationalization of Chinese medicine. Inspite of its wide application, security problems of Chinese medicine still occur from time to time, raising widespread concerns about its safety. Most of the studies either only partially discussed the intrinsic toxicities or extrinsic harmful residues in Chinese medicine, or briefly described detoxification and attenuation methods. It is necessary to systematically discuss Chinese medicine's extrinsic and intrinsic toxic components and corresponding toxicity detoxification or detection methods as a whole.

PURPOSE

This review comprehensively summarizes various toxic components in Chinese medicine from intrinsic and extrinsic. Then the corresponding methods for detoxification or detection of toxicity are highlighted. It is expected to provide a reference for safeguards for developing and using Chinese medicine.

METHODS

A literature search was conducted in the databases, including PubMed, Web of Science,Wan-fang database, and the China National Knowledge Infrastructure (CNKI). Keywords used were safety, toxicity, intrinsic toxicities, extrinsic harmful residues, alkaloids, terpene and macrolides, saponins, toxic proteins, toxic crystals, minerals, heavy metals, pesticides, mycotoxins, sulfur dioxide, detoxification, detection, processing (Paozhi), compatibility (Peiwu), Chinese medicine, etc., and combinations of these keywords. All selected articles were from 2006 to 2022, and each was assessed critically for our exclusion criteria. Studies describe the classification of toxic components of Chinese medicine, the toxic effects and mechanisms of Chinese medicine, and the corresponding methods for detoxification or detection of toxicity.

RESULTS

The toxic components of Chinese medicines can be classified as intrinsic toxicities and extrinsic harmful residues. Firstly, we summarized the intrinsic toxicities of Chinese medicine, the adverse effects and toxicity mechanisms caused by these components. Next, we focused on the detoxification or attenuation methods for intrinsic toxicities of Chinese medicine. The other main part discussed the latest progress in analytical strategies for exogenous hazardous substances, including heavy metals, pesticides, and mycotoxins. Beyond reviewing mainstream instrumental methods, we also introduced the emerging biochip, biosensor and immuno-based techniques.

CONCLUSION

In this review, we provide an overall assessment of the recent progress in endogenous toxins and exogenous hazardous substances concerning Chinese medicine, which is expected to render deeper insights into the safety of Chinese medicine.

Brush-like gold nanowires-anchored g-C3N4 nanosheets with tunable geometry for ultrasensitive and regenerative SERS detection of gaseous molecules

Strapping plasmonic substrate with a reliable ability to anchor molecules and achieve reproducible result provides trustworthy opportunities for flourishing surface-enhanced Raman scattering (SERS) technique. Herein, a facile controllable in-situ anisotropic growth strategy was exploited to anchor gold nanowires (Au NWs) onto two-dimensional g-C₃N₄ nanosheets (g-C₃N₄/Au NWs), facilitating a sensitive and recyclable SERS sensor for gaseous analytes. Benefiting from the attractive enrichment effect of the brush-like surface formed by numerous small Au NWs as well as their rich nanotips-mediated enhancement capability, the hybrid substrate showed an outstanding performance in SERS-based detection of trace 4-Aminothiophenol (4-ATP) molecules, demonstrating a monitoring limitation down to 10^-8 M even in atmosphere. Satisfyingly, under visible light illumination, the efficient green photocatalytic ability derived from the g-C₃N₄ supporting matrix rendered reusable capability for the substrate, whose SERS signal was kept at a persistent high level throughout 6 cycles. Attributed to the narrow line width of SERS spectrum, the 4-ATP assay under the interference of 2-naphthalenethiol (2-NAT) was acquired in gas phase and the dependable recovery rates from 85.4 to 93.9% were confirmed as well. Thanks to the intriguing features including excellent sensitivity and recyclability, the g-C₃N₄/Au NWs substrate proposed here will pave the way toward the potential application of SERS technique in multiplexed gaseous detection.

Detection of thiram on fruit surfaces and in juices with minimum sample pretreatment via a bendable and reusable substrate for surface-enhanced Raman scattering

BACKGROUND

Surface-enhanced Raman scattering (SERS) substrates based on metallic nanoparticles locked in some flexible materials have great potential for rapid detection of pesticide residues in foods, but these substrates are generally not reusable.

RESULTS

A bendable and reusable sponge based on polydimethylsiloxane (PDMS) and Au nanospheres was synthesized and employed as SERS substrate to analyze thiram on the surfaces of apples and grapes (20-1000 ng cm^-2 ) and in their juices (0.5-5.0 mg L^-1 ) with minimum sample pretreatments. The lowest detectible concentrations for thiram in fruit juices and on fruit skins were 0.5 mg L^-1 and 20 ng cm^-2 , respectively. The Au-PDMS substrate had acceptable intra-reproducibility for SERS analysis of thiram in fruit juices and on fruit skins, resulting in 3.6-16.9% relative standard deviation (RSD) for the SERS signal of the primary peak of thiram. Moreover, the Au-PDMS substrate exhibited distinguished reusability and stability, which could provide a reproducible SERS signal of thiram in apple juice even after the substrate being reused ten times (RSDs for the three major characteristic peaks of thiram were 2.7-10.5% during the ten reused cycles).

CONCLUSION

This flexible and reusable Au-PDMS SERS substrate for thiram detection could be readily extended to the analysis of other trace chemicals in a broad range of foods, providing a new possibility for SERS application. © 2022 Society of Chemical Industry.

The physio-chemical properties and applications of 2D nanomaterials in agricultural and environmental sustainability

Global hunger and nutritional deficiency demand the advancement of existing and conventional approaches to food production. The application of nanoenabled strategies in agriculture has opened up new avenues for enhancing crop yield and productivity. Recently, two-dimensional (2D) nanomaterials (NMs) have manifested new possibilities for increasing food production and nutrition. Graphene nanosheets, the 2D form of graphene has been exemplary in enhancing the loading capacity of agro-active ingredients, their target-specific delivery, bioavailability, and controlled release with slow degradation, resulting in the increased shelf-life/active time of the agro-active components. Also, the development of novel formulations/composites of MXenes and Transition Metal Dichalcogenides (TMDs) can foster plant growth, metabolism, crop production, protection and improvement of soil quality. Additionally, the 2D NM-based biosensors can monitor the nutrient levels and other parameters affecting agronomical traits in plants. This review provides an insight into the details of 2D NM synthesis and functionalization methods. Notably, the review highlights the broad-range of 2D NM applications and their suitability in the development of nanotechnology-based agriformulations. The 2D NM-based derivatives have shown immense potential in enhancing the pedologic parameters, crop productivity, pest-protection and nutritional value. Thus, assisting in achieving food and environmental sustainability goals.

Sensitive and handy detection of pesticide residue on fruit surface based on single microsphere surface-enhanced Raman spectroscopy technique

HYPOTHESIS

Surface-enhanced Raman spectroscopy (SERS) has become an emerging and reliable tool for detecting pesticide residues due to its high sensitivity, fast testing speed and easy sample handling. SERS active substrates are the key to achieve efficient and sensitive detection. However, for the most widely used noble metal nanoparticles, there are problems of high noble metal nanoparticle usage and random aggregation. The micron-scale Raman spot is focused on multiple randomly aggregated nanoparticles during the test, resulting in poor reproducibility. Therefore, the development of micron-scale cost-effective SERS substrates with good reproducibility and simple detecting method is of great significance in practical detection.

EXPERIMENTS

Through deposition of silver nanoparticles (Ag-NPs) by chemical reduction on the surface of monodisperse sulfonated polystyrene (SPS) microspheres, micron-sized PS@Ag-NPs core-shell microspheres were prepared with excellent SERS activity. After that, two simple protocols (Method I and Method II) were explored for the determination of thiram on apple epidermis.

FINDINGS

Based on our developed strategy of the single microsphere SERS technique, we successfully fabricated uniform PS@Ag-NPs substrate with high SERS activity and excellent detection sensitivity. The single microsphere SERS technique possesses the capability of anti-dilutability and the utilization of ultra-low PS@Ag-NPs microsphere dosage, realizing qualitative and quantitative detection of thiram on apple with detection limits far below the standard stipulated by China and the European Union.

Surface-Enhanced Raman Spectroscopic Investigation of PAHs at a Fe3O4@GO@Ag@PDA Composite Substrates

A method for surface-enhanced Raman spectroscopy (SERS) sensing of polycyclic aromatic hydrocarbons (PAHs) is reported. Fe₃O₄@PDA@Ag@GO is developed as the SERS substrate prepared by classical electrostatic attraction method based on the enrichment of organic compounds by graphene oxide (GO) and polydopamine (PDA) and the good separation and enrichment function of Fe₃O₄. The morphology and structure of the SERS substrate were represented by transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) and the UV–visible absorption spectrum (UV–vis spectra). The effect of different temperatures on SERS during synthesis was investigated, and it was found that the best effect was achieved when the synthesis temperature was 90 °C. The effect of each component of Fe₃O₄@PDA@Ag@GO nanocomposites on SERS was explored, and it was found that Ag NPs are of great significance to enhance the Raman signal based on the electromagnetic enhancement mechanism; apart from enriching the polycyclic aromatic hydrocarbons (PAHs) through π–π interaction, GO also generates strong chemical enhancement to the Raman signal, and PDA can prevent Ag from shedding and agglomeration. The existence of Fe₃O₄ is favored for the fast separation of substrate from the solutions, which greatly simplifies the detection procedure and facilitates the cycle use of the substrate. The experimental procedure is simplified, and the substrate is reused easily. Three kinds of PAHs (phenanthrene, pyrene and benzanthene) are employed as probe molecules to verify the performance of the composite SERS substrate. The results show that the limit of detection (LOD) of phenanthrene pyrene and benzanthene detected by Fe₃O₄@PDA@Ag@GO composite substrate are 10⁻⁸ g/L (5.6 × 10⁻¹¹ mol/L), 10⁻⁷ g/L (4.9 × 10⁻¹⁰ mol/L) and 10⁻⁷ g/L (4.4 × 10⁻¹⁰ mol/L), respectively, which is much lower than that of ordinary Raman, and it is promising for its application in the enrichment detection of trace PAHs in the environment.