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This study developed an in-field analytical technique for food samples by integrating filtration into a surface-enhanced Raman spectroscopy (SERS) microchip. This microchip embedded a filter membrane in the chip inlet to eliminate interfering particulates and enrich target analytes. The design and geometry of the channel were optimised by finite-elemental method (FEM) to tailor variations of flow velocity (within 0–24 μL/s) and facilitate efficient mixing of the filtrate with nanoparticles in two steps. Four pesticides (thiabendazole, thiram, endosulfan, and malathion) were successfully detected either individually or as a mixture in strawberries using this sensor. Strong Raman signals were obtained for the four studied pesticides and their major peaks were clearly observable even at a low concentration of 5 µg/kg. Limits of detection of four pesticides in strawberry extract were in the range of 44–88 μg/kg, showing good sensitivity of the sensor to the target analytes. High selectivity of the sensor was also proved by successful detection of each individual pesticide as a mixture in strawberry matrices. High recoveries (90–122%) were achieved for the four pesticides in the strawberry extract. This sensor is the first filter-based SERS microchip for identification and quantification of multiple target analytes in complex food samples. [ABSTRACT FROM AUTHOR]

A nanocomposite based on nanofibrillar cellulose (NFC) coated with gold–silver (core-shell) nanoparticles (Au@Ag NPs) was developed as a novel surface-enhanced Raman spectroscopy (SERS) substrate. SERS performance of NFC/Au@Ag NP nanocomposite was tested by 4-mercaptobenzoic acid. The cellulose nanofibril network was a suitable platform that allowed Au@Ag NPs to be evenly distributed and stabilized over the substrate, providing more SERS hotspots for the measurement. Two pesticides, thiram and paraquat, were successfully detected either individually or as a mixture in lettuce by SERS coupled with the nanocomposite. Strong Raman scattering signals for both thiram and paraquat were obtained within a Raman shift range of 400–2000 cm−1 and a Raman intensity ~ 8 times higher than those acquired by NFC/Au NP nanocomposite. Characteristic peaks were clearly observable in all SERS spectra even at a low concentration of 10 μg/L of pesticides. Limit of detection values of 71 and 46 μg/L were obtained for thiram and paraquat, respectively. Satisfactory SERS performance, reproducibility, and sensitivity of NFC/Au@Ag NP nanocomposite validate its applicability for real-world analysis to monitor pesticides and other contaminants in complex food matrices within a short acquisition time. [ABSTRACT FROM AUTHOR]

Sol composition and ripening conditions are two important parameters in silica fiber production through the conventional sol–gel process. In the current study, silica nanofibers were successfully obtained via the electrospinning technique, and sol–gel formation occurred during this process. Based on previous reports, with the aim of increasing the selectivity, we used the molecular imprinted methodology to produce a selective medium via sol–gel electrospinning. In this process, sol–gel was formed during electrospinning and then, the backbone polymer was removed by heating. To obtain a thin layer of silica nanofibers, the influencing parameters such as backbone polymer types, imprinting time and the components ratio were explored. The data obtained from Fourier transform infrared spectroscopy and thermogravimetric analysis revealed that the polyamide moiety was removed after heating. Also, the scanning electron microscopy images indicated the geometry of the silica nanofibers before and after heating. The extraction efficiency of the electrospun silica nanofiber mat was compared with the same silica precursor sol–gel produced by bulk and electrochemical approaches. The data obtained from the online micro-solid phase extraction-liquid chromatography analysis demonstrated the superiority of the electrospun silica nanofibers. After optimizing the entire procedure, the method was validated. The linearity of the analyte is in the range of 6–400 μg L−1, while the LOD value is 1.8 μg L−1 and the inter- and intra-day RSDs% are less than 9.6%. The method was conveniently applied to the spiked and un-spiked Zayanderood river, garden stream, and tap water samples with relative recovery percentages of up to 109%. [ABSTRACT FROM AUTHOR]

The high abundance of acetone ((CH 3 ) 2 C═O), which makes it a good candidate for oxygenated molecules, and the high reactivity of oxygen atoms in the first excited state O( 1 D) are two well-known facts in the chemistry of the atmosphere. In this research, we prove that the singlet oxygen and acetone system is capable of proceeding through multiwell multipath reactions, leading to the production of several organic aerosols. Hence, the nature of species released by the (CH 3 ) 2 C═O + O( 1 D) reaction to air can be clarified by profound attention to the possible routes. To verify this, the singlet potential energy surface (PES) of the acetone + O( 1 D) reaction is investigated by using various validated quantum chemistry approaches, especially the high-cost BD(TQ) method. By the carefully chosen theoretical methods, we forecast all possible multistep routes with high accuracy for the production of possible adducts in reliable conditions. Also, we use the kinetic results of the well-proven theories (TST and RRKM) to show the importance and atmospheric relevance of the simulated reactions. So, the rate constants of the (CH 3 ) 2 C═O + O( 1 D) reaction channels are computed at a large temperature range employing precise energetics and partition functions to show which products have a high percentage of yield. Moreover, the competitive canonical unified statistical (CCUS) model is utilized to show whether pressure influences the products generated by barrierless reactions. In addition, the thermodynamic functions of stationary points (at 298 K) and the rate constants of the found reaction routes demonstrate that the reaction adducts are very stable, so the reverse reactions have less importance compared to the forward reactions. In summary, this study illustrates how designed reaction routes could play a vital role in secondary aerosol formation in the atmosphere.