Rapid and ultrasensitive detection of thiram and carbaryl pesticide residues in fruit juices using SERS coupled with the chemometrics technique.

A gold nanogap substrate was used to measure the thiram and carbaryl residues in various fruit juices using surface-enhanced Raman scattering (SERS). The gold nanogap substrates can detect carbaryl and thiram with limits of detection of 0.13 ppb (0.13 µgkg-1) and 0.22 ppb (0.22 µgkg-1). Raw SERS data were first preprocessed to reduce noise and undesirable effects and, were later used for model creation, implementing classification, and regression analysis techniques. The partial least-squares regression models achieved the highest prediction correlation coefficient (R2) of 0.99 and the lowest root mean square of prediction value below 0.62 ppb for both pesticide-infected juice samples. Furthermore, to differentiate between juice samples contaminated by both pesticides and control (pesticide-free), logistic-regression classification models were produced and achieved the highest classification accuracies of 100% and 99% for contaminated juice containing thiram and 100% accurate results for contaminated juice containing carbaryl. This indicates that the gold nanogap surface has significant potential for achieving high sensitivity in detecting trace contaminants in food samples.

Thiram Determination in Milk Samples by Surface Plasmon Resonance Based on Molecularly Imprinted Polymers and Sulphur-Doped Titanium Dioxide.

In this work, a new surface plasmon resonance (SPR) sensor based on sulphur-doped titanium dioxide (S-TiO2) nanostructures and molecularly imprinted polymer (MIP) was presented for thiram (THI) determination in milk samples. Firstly, the S-TiO2 nanomaterial with a high product yield was prepared by using a facile sol-gel hydrolysis technique with a high product yield. After that, UV polymerization was carried out for the preparation of the THI-imprinted SPR chip based on S-TiO2 using a mixture including ethylene glycol dimethacrylate (EGDMA) as the cross-linker, N,N'-azobisisobutyronitrile (AIBN) as the initiator, and methacryloylamidoglutamicacid (MAGA) as the monomer. The reliability of the sensor preparation procedure has been successfully proven by characterization studies of the prepared nanomaterials and SPR chip surfaces through spectroscopic, microscopic, and electrochemical methods. As a result, the prepared SPR sensor showed linearity in the range of 1.0 × 10-9-1.0 × 10-7 M with a detection limit (LOD) of 3.3 × 10-10 M in the real samples, and a sensor technique for THI determination with high sensitivity, repeatability, and selectivity can be included in the literature.

Mechanistic understanding of nanoparticle interactions to achieve highly-ordered arrays through self-assembly for sensitive surface-enhanced Raman scattering detection of trace thiram.

Over the last few decades, there is increasing worldwide concern over human health risks associated with extensive use of pesticides in agriculture. Developing excellent SERS substrate materials to achieve highly sensitive detection of pesticide residues in the food is very necessary owing to their serious threat to human health through food chains. Self-assembled metallic nanoparticles have been demonstrated to be excellent SERS substrate materials. Hence, alkanethiols-protected gold nanoparticles have been successfully prepared for forming larger-scale two-dimensional monolayer films. These films can be disassembled into a fluid state and re-assembled back to crystallized structure by controlling surface pressure. Further investigations reveal that their self-assembled structures are mainly dependent on the diameter of gold nanoparticles and ligand length. These results suggest that the size ratio of nanoparticle diameter/ligand length within the range of 4.45-2.35 facilitates the formation of highly ordered 2D arrays. Furthermore, these arrays present excellent Surface-Enhanced Raman Scattering performances in the detection of trace thiram, which can cause environmental toxicity to the soil, water, animals and result in severe damage to human health. Therefore, the current study provides an effective way for preparing monodispersed hydrophobic gold nanoparticles and forming highly ordered 2D close-packed SERS substrate materials via self-assembly to detect pesticide residues in food. We believe that, our research provides not only advanced SERS substrate materials for excellent detection performance of thiram in food, but also novel fundamental understandings of self-assembly, manipulation of nanoparticle interactions, and controllable synthesis.

Glutathione­iron hybrid nanozyme-based colorimetric sensor for specific and stable detection of thiram pesticide on fruit juices.

Given the potential dangers of thiram to food safety, constructing a facile sensor is significantly critical. Herein, we presented a colorimetric sensor based on glutathione­iron hybrid (GSH-Fe) nanozyme for specific and stable detection of thiram. The GSH-Fe nanozyme exhibits good peroxidase-mimicking activity with comparable Michaelis constant (Km = 0.551 mM) to the natural enzyme. Thiram pesticides can specifically limit the catalytic activity of GSH-Fe nanozyme via surface passivation, causing the change of colorimetric signal. It is worth mentioning that the platform was used to prepare a portable hydrogel kit for rapid qualitative monitoring of thiram. Coupling with an image-processing algorithm, the colorimetric image of the hydrogel reactor is converted into the data information for accurate quantification of thiram with a detection limit of 0.3 µg mL-1. The sensing system has good selectivity and high stability, with recovery rates in fruit juice samples ranging from 92.4% to 106.9%.

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.

Ag-modified CuO cavity arrays as a SERS-electrochemical dual signal platform for thiram detection.

Rapid and sensitive determination of pesticide residues in fruits and vegetables is critical for human health and ecosystems. This paper used an Ag-modified CuO sphere-cavity array (CuO@Ag) electrode as a thiram SERS/electrochemical dual readout detection platform. Numerous Raman "hotspots" generated by uniformly distributed silver nanoparticles, charge transfer at the CuO@Ag interface, and the formation of Ag-thiram complexes contribute to the significant enhancement of this SERS substrate, which results in excellent SERS performance with an enhancement factor up to 1.42 × 106. When using SERS as the readout technique, the linear range of the substrate for thiram detection was 0.05-20 nM with a detection limit (LOD) of up to 0.0067 nM. Meanwhile, a correlation between the value of change in current density and thiram concentration was established due to the formation of stable complexes of thiram with Cu2+ generated at specific potentials. The linear range of electrochemical detection was 0.05-20.0 µM, and the detection limit was 0.0167 µM. The newly devised dual-readout sensor offers notable sensitivity and stability. The two signal readout methods complement each other in terms of linear range and detection limit, making it a convenient tool for assessing thiram residue levels in agro-food. At the same time, the combination of commercially available portable equipment makes on-site monitoring possible.

Preparation of cellulose-based flexible SERS and its application for rapid and ultra-sensitive detection of thiram on fruits and vegetables.

In response to the prevalent issue of thiram as a common pesticide residue on the surface of fruits and vegetables, our research team employed an acidic hydrated metal salt low co-fusion solvent to dissolve cellulose lysis slurry. Subsequently, a regenerated cellulose membrane (RCM) was successfully prepared via sol-gel method. Uniformly sized Ag nanoparticles (NPs) were deposited on RCM utilizing the continuous ion layer adsorption and reaction (SILAR) technique. The resulting Ag NPs/RCM flexible surface-enhanced Raman spectroscopy (SERS) substrates exhibited a minimum detection limit of 5 × 10-9 M for Rhodamine 6G (R6G), demonstrating good uniformity (RSD = 4.86 %) and reproducibility (RSD = 3.07 %). Moreover, the substrate displayed a remarkable sensitivity of 10-10 M toward thiram standard solution. Given its inherent flexibility, the substrate proves advantageous for the detection of three-dimensional environments such as fruit and vegetable surfaces, and its practicality has been confirmed in the detection of thiram residue on apples, tomatoes, pears, and other fruits and vegetables.

Green and sustainable self-cleaning flexible SERS base: Utilized for cyclic-detection of residues on apple surface.

Advances in flexible SERS substrates has made it possible to approach the ultimate goal of rapid in-situ monitoring of fruit and vegetable safety, but its vulnerability under laser ablation results in low utilization. In order to solve this problem, a 3D framework of TiO2-doped PVDF\PVP polymer was utilized to self-assemble gold-silver core-shell nanorods (Au@Ag NRs) to prepare a flexible SERS substrate with good physical stability and self-cleaning properties. This substrate showed excellent detection limit and recyclability after the detection of three pesticide residues in apple peel. The LOD of methyl-parathion (MP) was as low as 0.037 ng/cm2, with an RSD of 5.61 % for 5 cycle-detection. The recoveries of two additional pesticides thiram (TMTD) and chlorpyrifos (CPF) were 86.32 %-112.47 %. We hoped that this research will contribute to providing a recyclable and facile method for in-situ analysis of fruit and vegetable surface residues and functional manufacture of flexible SERS substrates.