Tianxi Yang

Real-Time and in Situ Monitoring of Pesticide Penetration in Edible Leaves by Surface-Enhanced Raman Scattering Mapping

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.

Evaluation of the Penetration of Multiple Classes of Pesticides in Fresh Produce Using Surface‐Enhanced Raman Scattering Mapping

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.

Alteration of the nonsystemic behavior of the pesticide ferbam on tea leaves by engineered gold nanoparticles

A model system consisting of a nonsystemic 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 h, the ferbam-AuNPs complex rapidly penetrated into the leaf to a depth of approximately 190 μm, about (1)/3 to (1)/2 of the leafs 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 nonsystemic 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.

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

Understanding pesticide behavior in plants is important for effectively applying pesticides and in reducing pesticide exposures from 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. The systemic pesticide thiabendazole and the nonsystemic pesticide ferbam can penetrate into the live leaves with depths of 225 and 130 μm, respectively, and the harvested leaves with depths of 180 and 18 μm, respectively, after 48 h of exposure. The effects of leaf integrity and age on thiabendazole penetration were also evaluated on live basil leaves after 24 h of 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 the 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 younger leaves with a wet mass of 0.053 ± 0.007 g per leaf (15 days after leaf out, 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.

A green, facile, and rapid method for microextraction and Raman detection of titanium dioxide nanoparticles from milk powder

Titanium dioxide (TiO2) has been widely used as a common ingredient in numerous food products. Recently, the analysis of TiO2 nanoparticles (NPs) has attracted increasing attention due to potential risks to human health and the environment. Herein, we present a green, facile, and rapid method using flavonoid-assisted microextraction and Raman spectroscopy for TiO2 NPs (anatase, 21 nm) detection in real food samples. Flavonoids can bind onto TiO2 NPs, enabling the microextraction of the particles by ethyl acetate and sodium chloride. The extracted TiO2 NPs concentrate at the interlayer and are easily removed for analysis by Raman spectroscopy. By taking advantage of surface-enhanced Raman spectroscopy (SERS), we evaluated and selected the best binding flavonoid, myricetin (MYC) bound onto TiO2 NPs, and were able to achieve detection at concentrations as low as 0.2 mg L−1 TiO2 NPs in water. The method was successfully challenged in the presence of various interferences from common food components and different pH conditions. The recoveries determined using inductively coupled plasma mass spectrometry (ICP-MS) ranged from 66.6% to 88.3%. More important, the method showed good capability for the extraction and quantification of TiO2 NPs from infant milk powder dilutions. As flavonoids, ethyl acetate, and sodium chloride have low toxicity and are relatively abundant in the environment, this may be considered a green approach for TiO2 NP extraction and detection. The developed method in this study holds great potential for rapid (<1 h) detection of TiO2 NPs from food products.

Effectiveness of Commercial and Homemade Washing Agents in Removing Pesticide Residues on and in Apples

Removal of pesticide residues from fresh produce is important to reduce pesticide exposure to humans. This study investigated the effectiveness of commercial and homemade washing agents in the removal of surface and internalized pesticide residues from apples. Surface-enhanced Raman scattering (SERS) mapping and liquid chromatography tandem mass spectrometry (LC-MS/MS) methods were used to determine the effectiveness of different washing agents in removing pesticide residues. Surface pesticide residues were most effectively removed by sodium bicarbonate (baking soda, NaHCO3) solution when compared to either tap water or Clorox bleach. Using a 10 mg/mL NaHCO3 washing solution, it took 12 and 15 min to completely remove thiabendazole or phosmet surface residues, respectively, following a 24 h exposure to these pesticides, which were applied at a concentration of 125 ng/cm2. LC-MS/MS results showed, however, that 20% of applied thiabendazole and 4.4% of applied phosmet had penetrated into the apples following the 24 h exposure. Thiabendazole, a systemic pesticide, penetrated 4-fold deeper into the apple peel than did phosmet, a non-systemic pesticide, which led to more thiabendazole residues inside the apples, which could not be washed away using the NaHCO3 washing solution. This study gives us the information that the standard postharvest washing method using Clorox bleach solution for 2 min is not an effective means to completely remove pesticide residues on the surface of apples. The NaHCO3 method is more effective in removing surface pesticide residues on apples. In the presence of NaHCO3, thiabendazole and phosmet can degrade, which assists the physical removal force of washing. However, the NaHCO3 method was not completely effective in removing residues that have penetrated into the apple peel. The overall effectiveness of the method to remove all pesticide residues diminished as pesticides penetrated deeper into the fruit. In practical application, washing apples with NaHCO3 solution can reduce pesticides mostly from the surface. Peeling is more effective to remove the penetrated pesticides; however, bioactive compounds in the peels will become lost too.

Investigation of degradation and penetration behaviors of dimethoate on and in spinach leaves using in situ SERS and LC-MS

To investigate the degradation and penetration behaviors of the organophosphate insecticide dimethoate applied on spinach leaves, in situ SERS and LC-MS methods were used to detect dimethoate residue on&in spinach leaves picked on different days after treatment (DAT). The SERS and LC-MS methods determined that the dimethoate degradation rate followed first-order kinetics, with a half-life of 3.56 or 4.13days, depending on the respective method. The correlation coefficient of quantification value of these two methods was 0.9562. With the SERS method, we detected most of the penetrated dimethoate in the depth of 60-110μm. With the LC-MS method, we detected dimethoate up to 0.17ng in leaves and that the dimethoate on:in ratio of spinach leaves ranged from 562.25 on 0 DAT to 5.23 on 14 DAT. The combination of these two methods facilitated a better understanding of the behavior and biological fate of pesticides in a complex biological system.

A Triple Functional Approach To Simultaneously Determine the Type, Concentration, and Size of Titanium Dioxide Particles

The large-scale manufacturing and use of titanium dioxide (TiO2) particles in food and consumer products significantly increase the likelihood of human exposure and release into the environment. We present a simple and innovative approach to rapidly identify the type (anatase or rutile), as well as to estimate, the size and concentration of TiO2 particles using Raman spectroscopy and surface-enhanced Raman spectroscopy (SERS). The identification and discrimination of rutile and anatase were based on their intrinsic Raman signatures. The concentration of the TiO2 particles was determined based on Raman peak intensity. Particle sizes were estimated based on the ratio between the Raman intensity of TiO2 and the SERS intensity of myricetin bound to the nanoparticles (NPs), which was proven to be independent of TiO2 nanoparticle concentrations. The ratio that was calculated from the 100 nm particles was used as a cutoff value when estimating the presence of nanosized particles within a mixture. We also demonstrated the practical use of this approach when determining the type, concentration, and size of E171: a mixture that contains TiO2 particles of various sizes which are commonly used in many food products as food additives. The presence of TiO2 anatase NPs in E171 was confirmed using the developed approach and was validated by transmission electron micrographs. TiO2 presence in pond water was also demonstrated to be an analytical capability of this method. Our approach shows great promise for the rapid screening of nanosized rutile and anatase TiO2 particles in complex matrixes. This approach will strongly improve the measurement of TiO2 quality during production, as well as the survey capacity and risk assessment of TiO2 NPs in food, consumer goods, and environmental samples.

Surface-Enhanced Raman Spectroscopy: A Tool for All Classes of Food Contaminants

Our food system is vulnerable and can be contaminated intentionally and unintentionally by microbes, chemicals, and engineered nanomaterials. Early-on detection of these contaminants in the food supply chain is critically important to keep our food safe. Surface-enhanced Raman spectroscopy (SERS) is, perhaps, the only technique that has been explored for detecting all three classes of contaminants that cannot be optically seen. In this short article, we will briefly summarize the current status of SERS in studying each of the three classes of contaminants, and the research challenges and opportunities.