The study aimed to extend the applications of surface-enhanced Raman scattering (SERS) – recently one of the most promising and widely employed technique in food safety and quality monitoring – towards determination of two analytes in a single step for the first time. Thus, an ultra-sensitive and selective SERS based detection platform for the simultaneous determination of pesticides namely acetamiprid (AC) and 2,4-dichlorophenoxyacetic acid (2,4-D) in matcha tea has been developed. Owing to the potential interference of different nutrients and pigments in complicated matrices, the matcha tea samples with and without spiking AC and 2,4-D, were percolated through a solid phase extraction cartridge. The eluate was introduced to the SERS Au@Ag nanostructure substrate for monitoring SERS signal with subsequent chemometrics modeling. Under the optimized experimental conditions, a linear calibration exhibited at GA-PLS model with RPD values of 6.53 and 6.23, and Rp values 0.9943 and 0.9923, respectively for AC and 2,4-D. The method was validated in both mixed and single spiking conditions successfully in terms of student's t- and F test at 95% confidence with satisfactory recovery percentages. An RSD value

Au@Ag nanostructure based SERS substrate for simultaneous determination of pesticides residue in tea via solid phase extraction coupled multivariate calibration

In the near future, single-molecule surface-enhanced Raman spectroscopy (SERS) is expected to expand the family of popular analytical tools for single-molecule characterization. We provide a roadmap for achieving single molecule SERS through different enhancement strategies for diverse applications. We introduce some characteristic features related to single-molecule SERS, such as Raman enhancement factor, intensity fluctuation, and data analysis. We then review recent strategies for enhancing the Raman signal intensities of single molecules, including electromagnetic enhancement, chemical enhancement, and resonance enhancement strategies. To demonstrate the utility of single-molecule SERS in practical applications, we present several examples of its use in various fields, including catalysis, imaging, and nanoelectronics. Finally, we specify current challenges in the development of single-molecule SERS and propose corresponding solutions.

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Roadmap for single-molecule surface-enhanced Raman spectroscopy

Exposure to commonly used pesticides poses significant health risks to humans and wildlife. Hence, accurate and sensitive pesticide residue testing methods are imperative to minimize potential health hazards. In this study, we report a method to detect several pesticide residues at trace levels utilizing colloidal gold nanoparticles and surface-enhanced Raman spectroscopy (SERS). Gold nanoparticles suspended in water have been found to enhance Raman scattering from 21 pesticides, including fungicides and insecticides, such as neonicotinoids and organothiophosphates. Measured limits of detection ranged from 0.001 to 10 parts per million (ppm). Furthermore, simultaneous detection of two pesticides, phosmet and thiram, in both a mixture solution and on apple skin, was performed using the SERS method and principal component analysis. The results presented here indicate that SERS coupled with colloidal gold nanoparticles is a potential useful tool for identifying pesticides at trace levels for food safety applications.

Determination of the Limit of Detection of Multiple Pesticides Utilizing Gold Nanoparticles and Surface-Enhanced Raman Spectroscopy.

Glutamic acid-functionalized graphene quantum dots (Glu-GQD) was prepared by pyrolysis of citric acid and glutamic acid and used as reducing agent and stabilizer to produce Glu-GQD/Au in the presence of tannic acid. The resulting Glu-GQD/Au was covalently connected with aptamer (Apt) of acetamiprid to obtain one redox probe with catalyst. The study shows that Glu-GQD/Au offers nanostar-like structure with average particle size of 102.5 nm, composing of several nanometer-sized gold nanocrystals with the rich of sharp edges and corners. The unique structure makes gold nanostars good electrocatalytic activity, which was further improved by combination with Glu-GQD. In the redox probe, Glu-GQD can carry out reversible redox reaction on the electrode surface due to its high electroactivity. Gold nanostars in-situ catalyzes redox reactions of Glu-GQD and leads to an improved electrochemical behavior. Aptamer can specifically bind with acetamiprid and produce sensitive and selective electrochemical response. The electrochemical aptasensor based on Glu-GQD/Au-Apt/graphene aerogel exhibits ultrahigh sensitivity and selectivity for detection of acetamiprid. The differential pulse voltammetric signal linearly decreases with increasing acetamiprid concentration in the range from 1.0 fM to 1 × 105 fM with detection limit of 0.37 fM (S/N = 3). The aptasensor has been successfully applied in electrochemical detection of acetamiprid in vegetables.

Electrochemical aptasensor for detection of acetamiprid in vegetables with graphene aerogel-glutamic acid functionalized graphene quantum dot/gold nanostars as redox probe with catalyst

Quantitative determination of peroxide value of edible oil by algorithm-assisted liquid interfacial surface enhanced Raman spectroscopy.

Accurate determination of the gutter oil represents a major food safety challenge. Here, we propose to use the surface enhanced Raman spectroscopy (SERS) with silver nanorod array substrates to detect the capsaicin, a marker of the gutter oil that is difficult to remove. The capsaicin has several characteristic SERS peaks at Δv = 807 cm−1, Δv = 1, 264 cm−1, and so forth, which correspond to the C39-C37-C43 stretching vibrational mode at the alkyl chain, the ring stretching vibrational mode, and so forth, confirmed by our density functional theory calculation. This SERS-based method enabled the rapid and highly sensitive detection of the gutter oil with minimum pretreatment. The concentration dependent SERS investigation shows that the SERS intensity of these characteristic peaks has a linear relationship with the capsaicin concentration when 1 mg/L < C < 60 mg/L. By combining a liquid phase extraction method and the SERS detection strategy, the capsaicin concentration as low as 30 mg/L can be detected from inoculated corn oil samples.

Rapid identification of gutter oil by detecting the capsaicin using surface enhanced Raman spectroscopy

The determination of pesticide residue on agricultural products is increasingly important.Exposure to pesticides can cause severe acute reactions in humans, including aplastic anemia and leukemia.In this work, we developed a rapid and sensitive method to detect acetamiprid pesticide residue based on surface-enhanced Raman scattering.Silver nanorod (AgNR) arrays were fabricated by oblique angle deposition technology and were used as SERS substrates.Prior to detection, the AgNR arrays were cleaned with nitric acid solution or a mixture of methanol and acetone.Compared to the unwashed AgNR arrays, the AgNR arrays washed with methanol and acetone shows a signal enhancement 1000 times greater than the unwashed AgNR array due to the effective removal of the impurities on its surface.The limit of detection of acetamiprid was determined to be 0.05 mg/L.In addition, the molecular structure of acetamiprid was simulated and the corresponding vibration modes of the characteristic bands of acetamiprid were calculated by density function theory.To demonstrate its practical application, the AgNRs array substrates were applied successfully to the rapid identification of acetamiprid residue on a cucumber's surface.These results confirmed possibility of utilizing the AgNRs SERS substrates as a new method for highly sensitive pesticide residue detection.

Highly Sensitive Silver Nanorod Arrays for Rapid Surface Enhanced Raman Scattering Detection of Acetamiprid Pesticides

Study on the components of isopropanol aqueous solution

This paper proposes a mid-infrared chiral structure, which consists of L-shaped indium tin oxide (ITO) films formed on self-assembled monolayer polystyrene microspheres in two orthogonal directions by oblique angle deposition technique. Experimental results demonstrate that the structure exhibit circular dichroism (CD) responses in the range of 2.5 - 4 µm. As the thickness difference of the ITO films in the two orthogonal directions increases, the CD response enhances. The reason is that the ITO films produce cross dipoles and their bigger differences in thickness bring to bigger phase differences in optical chirality. The experimental results also demonstrate that the CD signals are evidently stronger than those of the structure consisting of silver in the mid-infrared band. This work provides a new idea for the fabrication of mid-infrared chiral structures, which have potential applications in the polarization state control of mid-infrared lasers.

L-shaped ITO structures fabricated by oblique angle deposition technique for mid-infrared circular dichroism.

A new method based on surface enhanced Raman spectroscopy and deep learning is developed to classify the varieties of honey. This method used the difference of honey SERS spectrum to classify. Spectra of honey were accessed through preprocess. The classification method is found to be an effective approach to analyze substances, especially similar substances, so as to improving the accuracy of classification. Experimental results demonstrate that this approach is suitable for classification of similar substances.

Aixia Lu

Papers

Rapid identification of gutter oil by detecting the capsaicin using surface enhanced Raman spectroscopy

Highly Sensitive Silver Nanorod Arrays for Rapid Surface Enhanced Raman Scattering Detection of Acetamiprid Pesticides

Study on the components of isopropanol aqueous solution

L-shaped ITO structures fabricated by oblique angle deposition technique for mid-infrared circular dichroism.

Rapid Classification of Honey Varieties by Surface Enhanced Raman Scattering Combining with Deep Learning