Progress 07/01/23 to 06/30/24
Outputs
Target Audience: The PD presented research findings from this project to Wisconsin farmers at the Wisconsin Potato and Vegetable Growers Association Grower Education Conference in February 2024. The PD connected with and discussed the project with Carla Romano, a staff member from the Wisconsin Department of Agriculture, Trade and Consumer Protection (WI DATCP), at the Water@UW Think Tank Workshop in June 2024. The PD presented project-supported research findings to staff and scientists at the US EPA during the Innovations in Environmental Science Seminar Series in May 2024. The PD presented research findings from this project to representatives from state agencies, industry, academia, and the general public at the Water@UW Think Tank Workshop in June 2024. A Ph.D. student supported by this project presented findings to peers in academia and industry at the ACS Spring Conference in March 2024. Changes/Problems:The project's spending in the first year was delayed due to challenges in recruiting a Ph.D. student in Fall 2023. However, this issue was resolved when a new Ph.D. student joined the group in Spring 2024. Despite the delay, the project's progress was not significantly impacted, as the PD dedicated substantial time to conducting experiments, analyzing data, and processing results. What opportunities for training and professional development has the project provided?This project supported one Ph.D. student, who was directly mentored by the PD. The student met with the PD weekly and attended bi-weekly group meetings. Throughout the first-year of this project, the student received training in experimental design, implementation, data analysis, scientific writing, and presentation skills. The student gave an oral presentationtitled "Quantitative Insights into the Relationship Between the Concentrations and SERS Intensities of Neonicotinoids" at the ACS Spring 2024 National Conference in New Orleans, LA. Additionally, the student published a paper titled "Emerging Investigator Series: Quantitative Insights into the Relationship Between the Concentrations and SERS Intensities of Neonicotinoids in Water" in Environmental Science: Nano. This project also provided opportunities for the Ph.D. student to mentor two undergraduate students, who were trained to conduct rigorous scientific experiments and collect data under the Ph.D. student's supervision. How have the results been disseminated to communities of interest?The PD engaged with Wisconsin farmers, primarily potato growers who heavily rely on neonicotinoids as pesticides, by delivering a presentation at an outreach event organized by the UW-Madison Division of Extension. This event, the Wisconsin Potato and Vegetable Growers Association Grower Education Conference, was held in Stevens Point, Wisconsin, in February 2024. Additionally, the PD presented the project's findings to staff and scientists at the US EPA during the Innovations in Environmental Science Seminar Series in May 2024. Further outreach included a presentation at the Water@UW Think Tank Workshop, where the PD shared research findings with a diverse audience, including representatives from state agencies, industry, academia, and the general public. The PD's group also participated in the Engineering Expo, organized by the UW-Madison College of Engineering, where they demonstrated a handheld Raman spectrometer for pollutant analysis. This expo primarily engaged K-12 students from Dane County, Wisconsin. What do you plan to do during the next reporting period to accomplish the goals? We will continue to lower the limit of detection (LOD) for pesticides using AuNP/BC plasmonic passive samplers. Preliminary data indicates that the LOD can be further enhanced by reducing solution pH to facilitate citrate layer desorption or by adding halides that act as a bridge between pesticides and gold nanoparticles. We will conduct a systematic study to explore how these factors influence SERS sensor performance, not only for the three neonicotinoids we've focused on but also for the other pesticides and metabolites listed in our proposal. Additionally, we will investigate the underlying mechanisms of these improvements using advanced techniques, such as TEM EELS, to better understand gold nanoparticle surface chemistry. We aim to develop a flow-through device for real-time monitoring of pesticides using AuNP/BC plasmonic passive samplers. Preliminary findings show that increasing the sample volume improves the adsorption of neonicotinoids onto AuNP surfaces, ensuring more molecules interact with the concentrated AuNPs in the samplers. This suggests that a flow-through device could enhance SERS sensor performance by continuously supplying large volumes of water, simulating real-world conditions where water volume is not limited. We will continue refining and optimizing data processing algorithms to extract quantitative information from SERS spectra. In the first year, we demonstrated the potential to retrieve quantitative data from noisy or background-distorted spectra of typical neonicotinoids. Moving forward, we will further customize pre-processing procedures for different pesticides and apply a range of multivariate statistical tools, such as partial least squares regression and principal component analysis. Additionally, as our dataset grows, we will explore the application of machine learning models for more robust analysis. We will conduct several field campaigns in Wisconsin's Central Sands region to collect agricultural runoff samples potentially contaminated with the pesticides listed in our proposal. These field sampling efforts, supported by co-PD Groves, will allow us to further refine the sensors and data processing algorithms, focusing on minimizing interferences from real-world field samples.
Impacts
What was accomplished under these goals?
During the first year of this project, we focused primarily on achieving our firstgoal: quantifying five pesticides and their metabolites down to medium-to-high ng/L concentrations using plasmonic passive samplers. First, we synthesized, optimized, and characterized gold nanoparticle/bacterial cellulose (AuNP/BC) passive samplers designed for surface-enhanced Raman spectroscopic (SERS) applications. These samplers were tested for detecting five pesticides--imidacloprid, clothianidin, thiamethoxam, alachlor, and atrazine--in both deionized water and groundwater-sourced tap water. While SERS is known for its high sensitivity, its quantitative performance was initially limited due to an unclear relationship between pesticide concentrations and corresponding SERS signals. To address this, we conducted fundamental studies to better understand how SERS could be applied for the accurate quantification of neonicotinoid insecticides in water. We selected two widely used neonicotinoids--imidacloprid (IMD) and clothianidin (CLO)--as target analytes and studied their adsorption onto gold nanoparticle surfaces, a critical step for enhancing SERS signals. By investigating the adsorption equilibrium between these pesticides and gold nanoparticles, we modeled their behavior using classic adsorption isotherms, such as the Freundlich and Langmuir models. This allowed us to correlate SERS intensities with pesticide concentrations, enabling more accurate calibration curves. Our findings revealed that the relationship between SERS signals of neonicotinoids and their concentrations in water samples can be perfectly described using a Langmuir adsorption isotherm. Before the SERS "hot spots" were fully saturated, the SERS signals increased linearly with the adsorbed amount of neonicotinoid molecules within SERS "hot spots". This quantitative and mechanistic study was successful because of the use ofhigh-performance liquid chromatograph as a complementary analytical tool and hot spot normalized SERS to improve measurement reproducibility. To improve the detection limit down to high ng/L levels, we developed a custom data processing algorithm that correlates the concentration of neonicotinoids with their SERS spectral patterns. The algorithm assumes that SERS patterns shift as the molecular orientation on AuNP surfaces changes. Using this method, we extracted quantitative data even when background interference distorted the spectra.With citrate-coated gold nanoparticles as substrates, we tested the IMD, CLO, and thiamethoxam (THX)across a range of concentrations in both deionized and tap water, and achieveddetection limits as low as 0.001 μM. We also tackled challenges in SERS analysis with complex water matrices, including tap and lake water, by employing background subtraction techniques to reduce interferences. This process significantly enhanced the signal-to-noise ratio, allowing for clearer identification of the characteristic Raman bands of the three target neonicotinoids, even at environmentally relevantconcentrations. Our method demonstrated highaccuracy in detecting all neonicotinoidsacross multiple samples. In our continued development, we assessed factors like pH and the presence of other pesticides, confirming that the method works reliably in real-world conditions and whenmultiple pesticidescoexist inenvironments.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2024
Citation:
Liu, J. Lazarcik, and H. Wei,* Emerging investigator series: quantitative insights into the relationship between the concentrations and SERS intensities of neonicotinoids in water, Environmental Science: Nano, 2024, 11, 3294-3300
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