A pinboard by
Tianxi Yang

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.


A facile surface-enhanced Raman spectroscopy detection of pesticide residues with Au nanoparticles/dragonfly wing arrays

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

Fabrication of Fe3O4@SiO2@Ag magnetic–plasmonic nanospindles as highly efficient SERS active substrates for label-free detection of pesticides

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

Gecko-Inspired Nanotentacle Surface-Enhanced Raman Spectroscopy Substrate for Sampling and Reliable Detection of Pesticide Residues in Fruits and Vegetables

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

Detection of Pesticide Residues in Food Using Surface-Enhanced Raman Spectroscopy: A Review.

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

Investigation of Pesticide Penetration and Persistence on Harvested and Live Basil Leaves using Surface-Enhanced Raman Scattering Mapping.

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