I am a Ph.D. Candidate in Food Science. I detect pesticide residues on/in fresh produce with SERS
Real-time and in situ monitoring of pesticide residues on and in fresh produce
Pesticides are essential in modern agricultural practices. However, pesticide residues on and in fresh produce are of great food safety concerns. Understanding of the penetration behaviors of pesticides in fresh produce is of great significance for effectively applying pesticides and minimizing pesticide residues in food. Pesticides can be classified as either nonsystemic or systemic pesticides and they have different penetration characteristics in plant tissues. The degree of pesticides penetration in fresh produce affects their persistence over time. Internalized pesticides are not easily removed and may increase the available amount of pesticide, which could increase toxicity. The overall objective of this research is using innovative SERS mapping methods to investigate the behaviors and fate of pesticides on and in fresh produce in situ and in real time. SERS method is fast, simple, novel and very practical in real applications. It has lots of advantages such as ultrahigh sensitivity, unique spectroscopic fingerprint, and nondestructive data acquisition. SERS is a combination technique of Raman spectroscopy and nanotechnology. Different pesticides produce different chemical signatures of Raman signals. The use of gold nanoparticles (AuNPs) can enhance the Raman signals of pesticides more than a million times. In my research, I will take advantage of the fact that AuNPs can rapidly penetrate into plant tissues and apply them as probes to enhance the surface and internalized pesticide signals in situ. To the best of our knowledge, it is the first to use SERS method beyond pesticide detection but to study the pesticide penetration, degradation, and translocation in situ and in real time. Information obtained from these studies will help us to develop a better strategy to apply pesticides and reduce pesticide exposures from fresh produce and food. It can also provide a basis for setting residue tolerance levels and other regulatory considerations. Therefore, the outcome of these studies will greatly benefit to the long-term stability, safety and sustainability of agriculture and food system.
Abstract: Recent studies have conclusively show that the surface-enhanced Raman spectroscopy (SERS) has been widely used for chemical and biomolecular sensing. In this work, a facile, low-cost, green and rapid method to detect the pesticide residues is presented by using Au nanoparticles/dragonfly wing (AuNPs/DW) arrays as SERS-active substrate. The AuNPs/DW substrate is prepared by decorating the AuNPs on the DW surface with a simple two-step method, meanwhile, the microstructure properties and SERS signal are characterized by the scanning electron microscopy (SEM) and confocal microprobe Raman system. The experimental results show that compared with the conventional Raman spectroscopy, the AuNPs/DW substrate can enhance the Raman signal dramatically due to the largescale nanosized protrusions on the DW surface. The detection limit for rhodamine 6G (R6G) could reach as low as 10−8 M, which is important for the analysis of the most components and structures of samples. For the application of the three-dimensional AuNPs/DW, the micro-sample of thiram and carbaryl can also be detected quantitatively, and the detection limit both reach up to 10−7 M. The above phenomenon indicate that three-dimensional nanostructure AuNPs/DW is a promising SERS substrate for the test of samples in low concentration. Hence, our study will provide an effective approach for the rapid, sensitive and stable trace detection of organic molecular species.
Pub.: 01 Sep '16, Pinned: 08 Aug '17
Abstract: The cube-like Fe3O4@SiO2@Ag (FSA) nanocomposites with great SERS activity have been successfully synthesized by a layer-by-layer procedure in this paper. The cube-like Fe3O4@SiO2 core–shell structures were prepared via a new route and Ag nanoparticles were introduced onto their surface through a one-pot hydrothermal reaction. By controlling the reaction time, the coverage rate of Ag on the FSA surface could be tuned, and then a series of FSA composites were obtained. The SERS properties of these FSA composites were investigated using p-aminothiophenol (p-ATP) as the probe molecule. It was found that the FSA composites synthesized with a reaction time of 6 h showed the best SERS performance, and the detection limit for p-ATP could reach 1 × 10−7 M. For practical application, the FSA composites were also used to detect thiram, one of the dithiocarbamate fungicides that has been widely used as a pesticide in agriculture. The detection limit is as low as 1 × 10−6 M (0.24 ppm), lower than the maximal residue limit of 7 ppm in fruit prescribed by the US Environmental Protection Agency. The resulting substrate with high SERS activity, stability and strong magnetic responsivity makes the FSA composite a perfect choice for practical SERS detection applications.
Pub.: 01 Jul '16, Pinned: 08 Aug '17
Abstract: Flexible surface enhanced Raman scattering (SERS) substrates have advantage over the conventional rigid substrates as they can conform to the underlying object for the efficient extraction of target molecules from complex surfaces. Here, we demonstrate a simple and facile method for fabricating large area SERS-active, flexible and robust substrate for conformal and rapid extraction and detection of trace molecules. The novel SERS substrate was fabricated by embedding Ag nanorods into the polydimethylsiloxane (PDMS) polymer. The AgNRs embedded SERS substrates exhibited a high sensitivity and excellent reproducibility for analytes employed, demonstrating a direct application in trace detection for on-field applications. The in situ SERS measurements on these flexible substrates under mechanical tensile strain conditions were performed. Our results show that flexible SERS substrates can withstand a tensile strain (ε) value as high as 30% without losing SERS performance. The functionality of AgNRs embedded PDMS SERS substrate was demonstrated by directly extracting trace amount (∼10−9 g/cm2) of thiram pesticide directly from fruit peels via simple “paste and peel off” method.
Pub.: 27 Oct '16, Pinned: 08 Aug '17
Abstract: A nanocomposite based on cellulose nanofibers (CNFs) coated with silver nanoparticles (AgNPs) was developed in this study as a flexible and effective substrate for use in surface-enhanced Raman spectroscopy (SERS) analysis. An effective Raman indicator molecule, 4-aminothiophenol (pATP), was used to characterize AgNPs impregnated on CNFs. The CNF-AgNP films were used in SERS analysis to detect thiabendazole (TBZ) pesticides in apples. The influence of pH on the SERS spectra of TBZ was investigated because TBZ is a neutral molecule that has a low affinity for AgNPs. The pH of TBZ solution was decreased to below the TBZ’s pKa, thus enabling the electrostatic attraction between TBZ and AgNPs. CNFs can prevent the uncontrolled aggregation of AgNPs in low pH environment and serve as an effective AgNP/nanocellulose platform for SERS analysis. Results of this study demonstrate that CNF-AgNP nanocomposites can be used to rapidly detect TBZ pesticides in various food products.
Pub.: 15 Oct '16, Pinned: 08 Aug '17
Abstract: We have developed a Surface Enhanced Raman Scattering (SERS) active substrate based on silver nanoparticles grown by ultraviolet continuous wave laser irradiation of a silver-exchanged soda-lime glass. The formation of nanoparticles was highlighted by scanning electron microscopy and extinction spectroscopy. The high density and large size of the silver nanoparticles obtained by use of this method were found to be highly beneficial for detection of low-concentrated chemical species. Both Rhodamine 6G and methyl parathion, an active molecule of some commercial pesticides, were detected with high sensitivity compared to the results of the literature, proving the efficiency of our substrate as an efficient SERS platform.
Pub.: 06 Nov '16, Pinned: 08 Aug '17
Abstract: Chlorpyrifos, one of the broad-spectrum organophosphorus insecticides, is utilized extensively in agriculture. However, chlorpyrifos residues in food and water pose potential risks to human health. In this work, popcorn-like gold nanoparticles were synthesized under mild condition without any surfactant as template and serviced as SERS-active substrate for sensing chlorpyrifos by using a portable Raman spectrometer. The obtained substrate had extremely low background signal and remarkably enhanced SERS signal for detecting trace chlorpyrifos residues in fruit samples due to the “hot spots” formed between tips of gold nanopopcorns. As a result, the portable SERS-sensor system had a limit of detection at 1 μM of chlorpyrifos, which met the requirement of national standard.
Pub.: 05 Nov '16, Pinned: 08 Aug '17
Abstract: Fe3O4@SiO2@Ag magnetic–plasmonic nanospindles with efficient SERS performance and magnetic responsiveness have been successfully fabricated. Uniform and monodispersed Fe3O4@SiO2 nanospindles were prepared by a robust strategy through annealing the obtained β-FeOOH@SiO2 nanospindles in hydrogen atmospheres at 350 °C; the SiO2 shell could be regarded as an interlayer to maintain the morphology and offer a solid support for the further growth of Ag nanoparticles. Ag nanoparticles were introduced via in situ reduction of AgNO3, and the coverage rate of Ag nanoparticles anchored on Fe3O4@SiO2 was adjusted through regulating the AgNO3 concentration. Fe3O4@SiO2@Ag magnetic–plasmonic nanospindles can serve as highly efficient SERS active substrates with controllable magnetic aggregation due to steady enrichment of mass molecules in close proximity to abundant hot spots. Moreover, these nanospindles are used for label-free detection of thiram, and the detection limit is as low as 1 × 10−7 M (about 0.024 ppm), which is lower than the maximal residue limit of 7 ppm in fruits prescribed by the U.S. Environmental Protection Agency. Therefore, such magnetic–plasmonic nanospindles in the magnetic aggregation state may be potentially applied in rapid trace detection of residual pesticides or other specific analytes.
Pub.: 23 Dec '16, Pinned: 08 Aug '17
Abstract: Trace analysis of pesticides’ residue found in an agricultural product is a vital topic, which is still a time-consuming and unreliable approach. A fast and effective chemical sensing technique is therefore required. Surface-enhanced Raman spectroscopy (SERS) has been well developed for detecting target species at e.g., single molecule level. Herein, we used focus-ion beam and nano-indentation methods for fabricating Au/Ag/Au nanorods (NRs) and Au nanocavity array for subsequent SERS applications. The as-prepared SERS-active substrate was firstly evaluated by different wavelengths of Raman laser using rhodamine 6G as a probe molecule at low concentrations. The optimized Au/Ag/Au NRs array exhibited a strong SERS effect with an enhancement factor of 2.15 × 108. Furthermore, Au/Ag/Au NR substrates were competent to detect various types of pesticides' residue, i.e., permethrin, cypermethrin, carbaryl, and phosmet at low concentrations. Presumably high SERS signals may occur at the interface between pesticide molecules and NRs surface.
Pub.: 11 Apr '17, Pinned: 08 Aug '17
Abstract: We report a green and reusable surface-enhanced Raman scattering (SERS) film based on PMMA/Ag NPs/graphene. By using this Raman substrate, the SERS signals of R6G were significantly enhanced reaching a minimum detectable concentration of 5 × 10−8 M, due to having lots of hot spots adhered backside to the exposed graphene. The SERS film can be used for in-situ monitoring of trace thiram in apple juice with a detection limit of 1 × 10−6 M (0.24 ppm), which is below the maximal residue limit (MRL) of 7 ppm in fruit prescribed by the U.S. Environmental Protection Agency (EPA). Furthermore, reusability studies show that the SERS film can be used repeatedly. In addition, the graphene-enhanced SERS technique shows great potential applications for the in-situ detection and identification of pesticide residues in environmental water, fruits and vegetables.
Pub.: 23 Apr '17, Pinned: 08 Aug '17
Abstract: The binding of organometallic osmium carbonyl clusters onto the surface of gold nanoparticles ((10Os)CO-Au NPs) greatly enhanced the CO stretching vibration signal at ~2100cm(-1), which is relatively free from interference due to the absorbance of biomolecules. By utilizing the acetylcholinesterase (AChE) mediated hydrolysis of acetylthiocholine to thiocholine where the activity of AChE is inhibited by the presence of organophosphate pesticides (OPPs), the subsequent thiocholine-induced aggregation of (10Os)CO-Au NPs can be monitored by the change in color of the NPs solution and the variation in intensity of the SERS CO signal. The change in color offers a fast pre-screening method, whereas monitoring via SERS is used for greater accuracy and lower limit of detection (0.1 ppb) for quantitative detection. Its potential as a quick and accurate method of OPPs monitoring in consumer products was demonstrated in the detection of OPPs in real spiked samples such as beer.
Pub.: 12 May '17, Pinned: 08 Aug '17
Abstract: Rapid sampling and multicomponent detection are crucial for monitoring of pesticide residues analysis. Here, a gecko-inspired nanotentacle surface-enhanced Raman spectroscopy (G-SERS) platform is proposed for the first time for the simultaneous detection of three kinds of pesticides via a simple and intuitive “press and peeled-off” approach. The G-SERS platform obtained from seeding deposition of silver nanoparticles (Ag NPs) on 3D PDMS nanotentacle array is flexible and free-standing. Compared with other substrates, this G-SERS substrate can simultaneously provide outstanding SERS activity (enhancement factor = 1.2 × 107), superior reproducibility (RSD = 5.8%) and countless flexible nanoscale “tentacles” (∼6.7 × 108/cm2). Moreover, the high density of “tentacles” can freely approach the microarea and enable efficient target collection, which were confirmed by SEM and HPLC. By direct sampling from cucumber, apple, and grape surfaces, thiram (TMTD), methyl parathion (MPT), malachite green (MG), and their multiple components have been rapidly and reliably determined. For example, under the optimal conditions, a sensitivity of 1.6 ng/cm2 (S/N = 3) for TMTD was obtained on apple peels with a correlation coefficient (R) of 0.99. Therefore, the G-SERS substrate could offer a great practical potential for on-spot identification of various pesticide residues on real samples.
Pub.: 16 Jan '17, Pinned: 08 Aug '17
Abstract: The efficient extraction of targets from complex surfaces is vital for technological applications ranging from environmental pollutant monitoring to analysis of explosive traces and pesticide residues. In our present study, we proposed a proof-of-concept surface enhance Raman scattering (SERS) active substrate serving directly to the rapid extraction and detection of target molecules. The novel substrate was constructed by decorating the commercial tape with colloidal gold nanoparticles (Au NPs), which simultaneously provides SERS activity and “sticky” of adhesive. The utility of SERS tape was demonstrated by directly extracting pesticide residues in fruits and vegetables via a simple and viable “paste and peel off” approach. The obtained strong and easily distinguishable SERS signals allow us to detect various pesticide residues such as parathion-methyl, thiram, and chlorpyrifos in the real samples with complex surfaces including green vegetable, cucumber, orange, and apple.
Pub.: 25 Jan '16, Pinned: 08 Aug '17
Abstract: Pesticides directly pollute the environment and contaminate foods ultimately being absorbed by the human body. Their residues contain highly toxic substances that have been found to cause serious problems to human health even at very low concentrations. The gold standard method, gas/liquid chromatography combined with mass spectroscopy, has been widely used for the detection of pesticide residues. However, these methods have some drawbacks such as complicated pre-treatment and cleanup steps. Recent technological advancements of surface-enhanced Raman spectroscopy (SERS) has promoted the creation of alternative detection techniques. SERS is a useful detection tool with ultrasensitivity and simpler protocols. Present SERS-based pesticide residue detection often uses standard solutions of target analytes in conjunction with theoretical Raman spectra calculated by density functional theory (DFT), and actual Raman spectra detected by SERS. SERS is quite a promising technique for the direct detection of pesticides at trace levels in liquid samples, or on the surface of solid samples following simple extraction to increase the concentration of analytes. In this review, we highlight recent studies on SERS-based pesticide detection, including SERS for pesticide standard solution detection and for pesticides in/on food samples. Moreover, deep analysis of pesticide chemical structures, structural alteration during food processing, interaction with SERS substrates, and selection of SERS-active substrates are involved.
Pub.: 21 Jul '17, Pinned: 08 Aug '17
Abstract: A model system consisting of a non-systemic pesticide (ferbam), engineered gold nanoparticles (AuNPs) and a plant tissue (tea leaves) was investigated using surface enhanced Raman spectroscopy (SERS). Ferbam has no ability by itself to penetrate into tea leaves. When AuNPs were placed with ferbam onto the surface of tea leaves, however, the SERS signal of the ferbam-AuNPs complex was observed inside of the tea leaves. Within 1 hour, the ferbam-AuNPs complex rapidly penetrated into the leaf to a depth of approximately 190 μm, about 1/3 to ½ of the leaf's thickness. The rate of penetration was dependent on the size of AuNPs, with 30 nm AuNPs-ferbam penetrating more rapidly when compared with complexes made with the 50 and 69 nm AuNPs. These results clearly demonstrated an alteration of the non-systemic behavior of ferbam in the combined presence with AuNPs. This finding might lead to the development of some new pesticide formulations. Conversely, new toxicity issues may arise as the behaviors and fate of pesticides are altered significantly upon interaction with engineered NPs in the pesticide formulation or environment.
Pub.: 03 Jun '16, Pinned: 01 Aug '17
Abstract: Understanding pesticide behavior in plants is important for effectively applying pesticides and in reducing pesticide exposures from the ingestion. This study aimed to investigate the penetration and persistence of pesticides applied on harvested and live basil leaves. Surface-enhanced Raman scattering (SERS) mapping was applied for in situ and real-time tracking of pesticides over time using gold nanoparticles as probes. The results showed that after surface exposure of 30 min to 48 h, pesticides (10 mg/L) penetrated more rapidly and deeply into the live leaves than the harvested leaves. Systemic pesticide thiabendazole and the non-systemic pesticide ferbam can penetrate into the live leaves with depth of 225 μm and 130 μm, respectively than the harvested leaves with depth of 180 μm and 18 μm, respectively after 48-h exposure. The effects of leaf integrity and age on thiabendazole penetration were also evaluated on live basil leaves after 24-h exposure. Thiabendazole (10 mg/L) when applied onto intact leaves penetrated deeper (170 μm) than when applied onto damaged leaves (80 μm) prepared with 20 scrapes on the top surface of leaves. Older leaves with a wet mass of 0.204 ± 0.019 g per leaf (45 days after leaf out) allowed more rapid and deeper penetration of pesticides (depth of 165 μm) than when younger leaves with a wet mass of 0.053 ± 0.007 g per leaf (15 days after leaf out) were used (depth of 95 μm). The degradation of thiabendazole on live leaves was detected after 1 week whereas the apparent degradation of ferbam was detected after 2 weeks. In addition, the removal of pesticides from basil was more efficient when compared with other fresh produce possibly due to the specific gland structure of basil leaves. The information obtained here provides a better understanding of the behavior and biological fate of pesticides on plants.
Pub.: 11 Apr '17, Pinned: 21 Jul '17
Abstract: Pesticides are essential in modern agricultural practices. Detection of pesticides is an essential step in regulating and monitoring the levels of pesticides in the environment. Even though GC/LC-MS is often the gold standard method for pesticide detection, recent technological advancements has promoted the creation of alternative techniques, such as Surface Enhanced Raman Spectroscopy (SERS), that provide added advantages such as ultrasensitive detection, faster turnover, simpler protocols, in situ sampling, on-site capability and reduced cost. In this review, a comprehensive report of recent advances in SERS detection of synthetic chemical pesticides is given. The development and applications of the SERS technique for pesticide detection in both simple and complex matrices are discussed. The main advantages of using SERS for pesticide detection are highlighted, together with its limitations. Lastly, promising future trends and applications of SERS for pesticides detection are also discussed.
Pub.: 05 Jul '16, Pinned: 21 Jul '17
Abstract: Understanding pesticide penetration is important for effectively applying pesticides and in reducing pesticide exposures from food. This study aims to evaluate multiclass systemic and nonsystemic pesticide penetration in 3 representative fresh produce (apples, grapes, and spinach leaves). Surface-enhanced Raman scattering mapping was applied for in situ and real-time tracking of pesticide penetration over time. The results show that 100 mg/L of systemic pesticides, thiabendazole and acetamiprid, penetrated more rapidly and deeply with maximum depth around 220 μm after 48-h exposure into the tested fresh produce than 100 mg/L of nonsystemic pesticides, ferbam and phosmet, with maximum depth about 80 μm. The fact that 2 nonsystemic pesticides were also able to penetrate over time into all 3 fresh produce tested may raise additional food safety concerns. Comparatively, grapes were generally more resistant for pesticide penetration with all pesticides penetration depth below 80 μm compared to apples and spinach leaves. The information obtained here could provide technical support and guidance for accurate, effective, and safe application of pesticides and for the reduction of pesticide exposure from fresh produce.
Pub.: 07 Oct '16, Pinned: 21 Jul '17
Abstract: Understanding of the penetration behaviors of pesticides in fresh produce is of great significance for effectively applying pesticides and minimizing pesticide residues in food. There is lack, however, of an effective method that can measure pesticide penetration. Herein, we developed a novel method for real-time and in situ monitoring of pesticide penetration behaviors in spinach leaves based on surface-enhanced Raman scattering (SERS) mapping. Taking advantage of penetrative gold nanoparticles (AuNPs) as probes to enhance the internalized pesticide signals in situ, we have successfully obtained the internal signals from thiabendazole, a systemic pesticide, following its penetration into spinach leaves after removing surface pesticide residues. Comparatively, ferbam, a nonsystemic pesticide, did not show internal signals after removing surface pesticide residues, demonstrating its nonsystemic behavior. In both cases, if the surface pesticides were not removed, copenetration of both AuNPs and pesticides was observed. These results demonstrate a successful application of SERS as an effective method for measuring pesticides penetration in fresh produce in situ. The information obtained could provide useful guidance for effective and safe applications of pesticides on plants.
Pub.: 21 Apr '16, Pinned: 21 Jul '17
Abstract: A novel magnetically responsive and surface-enhanced Raman spectroscopy (SERS) active nanocomposite is designed and prepared by direct grafting of Au nanoparticles onto the surface of magnetic network nanostructure (MNN) with the help of a nontoxic and environmentally friendly reagent of inositol hexakisphosphate shortly named as IP6. The presence of IP6 as a stabilizer and a bridging agent could weave Fe3O4 nanoparticles (NPs) into magnetic network nanostructure, which is easily dotted with Au nanoparticles (Au NPs). It has been shown firstly that the huge Raman enhancement of Au-MNN is reached by an external magnetic collection. Au-MNN presenting the large surface and high detection sensitivity enables it to exhibit multifunctional applications involving sufficient adsorption of dissolved chemical species for enrichment, separation, as well as a Raman amplifier for the analysis of trace pesticide residues at femtomolar level by a portable Raman spectrometer. Therefore, such multifunctional nanocomposites can be developed as a smart and promising nanosystem that integrates SERS approach with an easy assay for concentration by an external magnet for the effective on-site assessments of agricultural and environmental safety.
Pub.: 17 Oct '13, Pinned: 21 Jul '17
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