Combining Headspace Solid-Phase Microextraction and Surface-Enhanced Raman Spectroscopy To Detect the Pesticide Fonofos in Apple Juice

Development and characterization of self-powered, highly sensitive optoelectronic device based on PVA-rGO nanofibers/n-Si

This study provided a promising way to fabricate low-cost and high-performance Poly (vinyl alcohol)-reduced graphene oxide (PVA-RGO) nanofibers/n-Si heterojunction photodetector. For this purpose, the hybrid heterojunction with a very-high rectification ratio (2.4 × 106) was achieved by successfully coating PVA-RGO nanofibers on n-Si wafer by electrospinning method. When the electro-optical analysis of the fabricated heterojunction photodetector under visible light depending on the light intensity, ultraviolet (UV) and infrared (IR) lights was examined in detail, it was observed that the photodetector exhibited both self-powered behavior and very high photo-response under each light sources. However, the highest optical performance was obtained under UV (365 nm) originated from PVA-RGO layer and IR (850 nm) light from both interfacial states between PVA-RGO nanofibers and Si and from Si layer. Under 365 nm UV light, the maximum performance values of R, D, ON/OFF ratio, normalized photo-dark-current ratio and external quantum efficiency (%) were obtained as 688 mA W-1, 1.15 × 1015Jones, 2.49 × 106, 8.28 × 1010W-1and 234%, respectively.

Research Status in the Use of Surface-Enhanced Raman Scattering (SERS) to Detect Pesticide Residues in Foods and Plant-Derived Chinese Herbal Medicines

Surface-enhanced Raman scattering (SERS) technology has unique advantages in the rapid detection of pesticides in plant-derived foods, leading to reduced detection limits and increased accuracy. Plant-derived Chinese herbal medicines have similar sources to plant-derived foods; however, due to the rough surfaces and complex compositions of herbal medicines, the detection of pesticide residues in this context continues to rely heavily on traditional methods, which are time consuming and laborious and are unable to meet market demands for portability. The application of flexible nanomaterials and SERS technology in this realm would allow rapid and accurate detection in a portable format. Therefore, in this review, we summarize the underlying principles and characteristics of SERS technology, with particular focus on applications of SERS for the analysis of pesticide residues in agricultural products. This paper summarizes recent research progress in the field from three main directions: sample pretreatment, SERS substrates, and data processing. The prospects and limitations of SERS technology are also discussed, in order to provide theoretical support for rapid detection of pesticide residues in Chinese herbal medicines.

SERS detection of foodborne pathogens in beverage with Au nanostars

The aim of this study is to develop a simple but rapid method for the determination of foodborne pathogens in complex matrices (beverages) by surface enhanced Raman spectroscopy (SERS) combined with Au nanostar solid-phase substrates. The star-shaped singlet Au nanostructure was formed on the surface of a stainless steel sheet by chemical replacement reaction. Rhodamine 6G verified the sensitivity and reproducibility of this substrate, and the relative standard deviations of the SERS intensity at 1312 cm-1, 1364 cm-1, and 1510 cm-1 displacements were 3.40%, 5.64%, and 3.48%, respectively. By detecting four pathogens in beverage samples on Au nanostar substrates, the utility of the SERS assay was demonstrated, while the combination of principal component analysis (PCA) and hierarchical cluster analysis (HCA) further enabled the isolation and identification of pathogens. The results of spiked beverages were validated in conventional culture identification and Vitek 2 Compact biochemical identification system experiments. Thus, this research demonstrated that Au nanostar substrates can be effectively utilized for the recognition of pathogenic bacteria and have immense promise to advance the progress of quick detection of foodborne pathogens and food safety.

Lotus leaf mastoid inspired Ag micro/nanoarrays on PDMS film as flexible SERS sensor for in-situ analysis of pesticide residues on nonplanar surfaces

Conventional surface-enhanced Raman scattering (SERS) molecular detection are based on hard and brittle substrate, which are not suitable for in-situ detection of analytes adsorbed on nonplanar surfaces. Here, we report a simple biomimetic synthesis method to fabricate lotus leaf mastoid structured AgNPs micro/nanoarrays as reliable SERS substrate. By ideal replicating mastoid structure of lotus leaf into a flexible and transparent PDMS film, followed by depositing plasmonic AgNPs, a powerful chemical sensor with high sensitivity and multiplex detecting capability is demonstrated. The employ of periodic mastoid structure array endows the sensor with high signal repeatability (RSD ∼ 8.6 %), solving the general repeatability problem of SERS substrates. In addition, the detailed designed flexible and transparent PDMS substrate is capable of identifying trace analytes on curved surfaces with excellent durability. In the proof-of-concept experiment, a limit of detection (LOD) of (10^-5 M to 10^-7 M) was achieved on a portable Raman device for three common pesticides residues (thiram, fonofos and triadophos) on dendrobium leaves and stem according to the molecular fingerprint, indicating its excellent in-situ detection capability. Further, the multiplex detection ability of the Ag/PDMS film is also demonstrated by analyzing the mixture of four typical analytes. Benefiting from its high signal uniformity, this flexible Ag/PDMS substrate also showed good quantitative detection capabilities.

Combining thin-film microextraction and surface enhanced Raman spectroscopy to sensitively detect thiram based on 3D silver nanonetworks

By coupling thin-film microextraction (TFME) with surface enhanced Raman scattering (SERS), a facile method was developed for the determination of thiram in the complex matrix (orange juice or grape peel). The substrate of TFME was made by self-assembling silver sol on the silicon wafer to form a three-dimensional (3D) silver nanonetwork structure, without adding any template, which was used for TFME and SERS detection, respectively. The substrate exhibits high reproducibility with a relative standard deviation of about 7.32 % in spot and spot SERS intensity. The SERS signal intensity at a shift of 1384 cm^-1 and the thiram concentration showed good linearity in the range of 0.01-5 µg/L and the linear correlation coefficient was 0.9912. The detection limit for thiram was found to be 0.01 µg/L. The TFME-SERS method was applied for the determination of thiram in fruit juice and the results were obtained very well. Therefore, this method is expected to play a role in the detection of trace pollutants.

Automatic Multi-Plug Filtration Cleanup Tip-Filtration with Ultra-Performance Liquid Chromatography/Tandem Mass Spectrometry Detection For 22 Pesticide Residues in Typical Vegetables

An automatic multi-plug filtration cleanup (m-PFC) tip-filtration method was developed to reduce the manual operation workload in sample preparation. In this work, m-PFC was based on multi-walled carbon nanotubes mixed with primary secondary amines and anhydrous magnesium sulfate (MgSO4) in a packed column for analysis of pesticide residues followed by ultra-performance liquid chromatography coupled with tandem mass spectrometry. Method validation was performed on 22 pesticide residues in carrot, spinach and leek, at spiked levels of 5, 10 and 50 μg/kg, respectively. The average recoveries were between 70.1 and 119.5% with associated relative standard deviations <20% (n = 6) indicating satisfactory accuracy and repeatability. Matrix-matched calibration curves were performed with the correlation coefficients (R2) higher than 0.9903 within a linearity range of 5-100 ng/mL. The limits of quantification were 5 μg/kg for all the pesticides in carrot, spinach and leek matrices. The developed method was successfully used to determine pesticide residues in market samples.

Ultrasensitive detection of pectin based on the decarboxylation reaction and surface-enhanced Raman spectroscopy

In the present study, a novel simple and sensitive method was developed for the determination of pectin based on the decarboxylation derivatization reaction and surface-enhanced Raman scattering (SERS) without complicated separation steps. The derivatization reaction can be controlled by the experimental parameters such as reaction time, temperature and the amount of hydrochloric acid. Additionally, the method was used to accurately and reliably detect pectin added in honey or apple, which can be detected at levels as low as 0.5 or 0.01 ppm, respectively. Based on the conventional decarboxylation reaction, a simple and sensitive SERS method was proposed for the detection of pectin, which shows potential for practical application.

Sensitive detection of ferbam by coupling solid phase microextraction with surface enhanced Raman spectroscopy based on Au nano-glass capillary

In this study, we developed an innovative approach that combines solid phase microextraction (SPME) with surface-enhanced Raman spectroscopy (SERS) to detect pesticide ferbam rapidly. An Au nano-glass capillary was fabricated by coating template-freely synthesized three-dimensional network Au nanostructures (3D-NW AuNSs) on the roughened surface of glass capillary and used for SPME and SERS respectively. Significant Raman signals were obtained by the SPME-SERS method, followed by detection of ferbam in water and orange juice samples with only 1 min SPME process. Results showed that Au nano-glass capillaries could achieve the detection of ferbam with limit of detection of 0.05 μg/L, and coefficient of determination (R²) of 0.9913. The recovery of predicted results was in the range of 88.46-103.29% and the relative standard deviation (RSD) was 3.5-8.2%. This study demonstrated potential capability of the SPME-SERS method for rapid (within 1 min) and sensitive detection of organic compounds in complex matrices. The SERS-active Au nano-glass capillary is easy to carry and operate, and is expected to play a role in the detection of trace pollutants.

Mechanical power driven SPME-SERS ultra-fast detection of illegal additives in aquaculture water

A dual-function (extraction and detection) porous silver fiber with high enhancement effect was constructed based on a convenient electrochemical etching method. The prepared silver fiber not only had high enrichment capacity and good Surface Enhanced Raman Spectroscopy (SERS) performance but also had good laser stability and uniformity. A strategy combining mechanical power and integration of solid phase extraction (SPME) and SERS detection was used. Driven by mechanical power, the analyte malachite green (MG) was enriched on the prepared silver fiber after 40 seconds, which can realize an ultra-fast and sensitive detection with a detection limit of 8.48 × 10-9 M. At the same time, this fiber can be regenerated after being treated with NaBH4. The silver fiber can be used for the detection of MG and CV after being immersed in NaBH4 solution for a few minutes. After 5 cycles of processing, the measurement signals of the silver fiber can reach 70% of the initial signals. The mechanical power driven SPME-SERS (MPD-SPME-SERS) integrated detection method can be used to analyse aquaculture water within 1 minute with a good linear relationship.

Dispersive solid-phase extraction using microporous metal-organic framework UiO-66: Improving the matrix compounds removal for assaying pesticide residues in organic and conventional vegetables

An efficient dispersive solid-phase extraction method was developed to trace pesticide residues in commonly consumed vegetables. In this method, UiO-66 with uniform micropores was used as sorbent, and gas chromatography-mass spectrometry was applied to detect the pesticides. Thanks to the size sieving action of uniform micropores, UiO-66 directly extracted the target pesticides from vegetable matrices and excluded the relatively large matrix compounds. This well eliminated the matrix effect. The important experimental conditions were evaluated by orthogonal array experimental design. In optimized conditions, good linearity (R² ≥ 0.99), detection limits (0.4-2.0 ng/g), recoveries (60.9-117.5%) and precision (relativestandarddeviations < 14.6%) were achieved. Moreover, the sorbent UiO-66 can be reused more than 20 times. These demonstrate a simple, reliable and robust method to screen the pesticide residues in vegetables. Furthermore, the validated method was applied to detect the pesticides in various organic and conventional vegetables.

Headspace Characterization and Quantification of Aromatic Organosulfur Compounds in Garlic Extracts Using Surface-Enhanced Raman Scattering with a Mirror-in-a-Cap Substrate

Background

Surface-enhanced Raman scattering (SERS) has been deployed in the analysis of food at solid and aqueous states. However, its capability has not been fully explored in headspace profiling.

Objective

To develop an innovative SERS method for analyzing headspace volatile compounds in foods.

Methods

A volatile-capture device was developed by depositing a film of silver nanoparticles in a vial cap to capture the volatiles released from a model flavor compound (garlic).

Results

SERS peaks at 1632, 1400, 1291, 1191, 731, and 577 cm−1 were identified in the headspace of the garlic sample, which was representative of an organosulfur compound (diallyl disulfide), and its concentration was determined at 135 ppm, which was comparable to the value determined using GC. Preparation and analysis could be carried out in &lt;10 min for the SERS method. The sensitivity of the SERS method (10 ppm), however, was slightly less than that of the GC method (5 pm).

Conclusions

The SERS method was able to quantify the concentration of diallyl disulfide in the headspace of a raw garlic ethanolic extract. Compared to GC, the SERS method had a much shorter analysis time and simpler sample preparation procedure than GC when analyzing large numbers of samples.

Highlights

The innovative “mirror-in-a-cap” substrate was simpler and faster than other reported SERS substrates used for this purpose. Additionally, SERS has much better portability and the potential for real-time monitoring of changes in the garlic headspace concentration during manufacturing and processing.

Combining microextraction methods with surface-enhanced Raman spectroscopy towards more selective and sensitive analyte detection by plasmonic metal nanoparticles

Raman signals of analytes can be enhanced on the surface of noble nanoparticles by generating SERS signals, which can be further enhanced using microextraction (ME) techniques.

Multi-phase detection of antioxidants using surface-enhanced Raman spectroscopy with a gold nanoparticle-coated fiber

The development of a method for multi-phase detection of antioxidants using surface-enhanced Raman spectroscopy (SERS) with a gold nanoparticle (AuNP)-coated fiber as a substrate is described. The AuNP-coated fiber was directly inserted into a multi-phase system containing model analytes of ascorbic acid, ascorbyl palmitate, and α-tocopherol, representing hydrophilic, amphiphilic, and lipophilic antioxidants, respectively. The AuNP-coated fiber enabled simultaneous detection of antioxidants present within the aqueous, interfacial, and organic phases of the multi-phase system. An oil-in-water emulsion was used as a model multi-phase system, where the antioxidant profiles of the three model analytes were successfully characterized. This method enables rapid, simultaneous, and non-destructive analysis of multiple antioxidants in complex multi-phase systems.