Progress 04/01/20 to 03/31/24
Outputs
Target Audience:Work over the duration of this FASE SEED project has been designed primarily for audiences of other scientists studying nanoparticle attachment and release in agricultural systems. Efforts to reach audiences have included presentation at scientific meetings, and completion of one master's thesis based on the work. An invited journal paper based on the thesis is in preparation. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?We worked closely with the students hired for the project to help them learn laboratory techniques needed to conduct the work, as well as to help them obtain the fundamental background to understand the work. Training included helping them learn to report on and present their work in a scientific setting. How have the results been disseminated to communities of interest?Results have been disseminated through two scientific conference presentations to date. An invitedjournal article describing the work is in preparation. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
The work conducted for this project was centered around two specific tasks: Task 1. Measurement of xDLVO parameters to allow prediction of the effect of extracellular polymeric substances (EPS) on nanoparticle attachment to produce surfaces.For this work, extensive measurements were made of xDLVO energy parameters for spinach leaves and extracellular polymeric substances (EPS), as well as rotten spinach leaves. Determination of xDLVO energy parameters on surfaces is done through calculations based on contact angles measured using multiple fluids. A large part of the work in this task involved method development, as reproducible measurement of contact angles on rough biological surfaces proved to be unexpectedly difficult. Typically more than 20 separate measurements with each of three fluids were needed to acquire enough data to determine values and error ranges for each surface, and care had to be taken to control evaporation. Some commonly-used fluids for xDLVO measurements exhibited interactions with surfaces and could not be used; for example, because water dissolved EPS, the surface energy of water decreased when placed in contact with EPS, making the resulting xDLVO energy values incorrect. Results of these measurements found the energy parameters of fresh spinach to be distinctly different from EPS and rotten spinach. EPS and rotten spinach exhibited nearly identical xDLVO energy parameters to one another, and these values were also very similar to previously published values for bacteria such as E. coli. Measurements of zeta potential were also conducted for this work as needed. A hypothesis driving the work was that the presence of EPS on produce surfaces would enhance attachment of nanoparticles. However, calculations with the resulting parameters suggested that, in fact, the opposite might be expected to be true for most mineral nanoparticles. I.e., nanoparticles would be less likely to exhibit favorable attachment to EPS and similar surfaces than to bare spinach leaf surfaces. Task 2. Quantification of nanoparticle attachment/detachment through direct imaging.The purpose of this task was to quantify nanoparticle attachment for correlation with xDLVO analyses conducted through Task 1. Nanoparticle attachment/detachment was measured through direct observation of attached nanoparticles using imaging with a high resolution scanning electron microscope (SEM). Emphasis in this work was on studying the attachment of titanium dioxide and zinc oxide nanoparticles, two mineral nanoparticles with similar surface energy characteristics, but distinctly different points of zero charge, allowing study of attachment/detachment under electrostatic conditions that favor retention or conditions that favor release. Significant effort in this task was focused on method development. Quantification of nanoparticle surface concentrations was done through the use of backscattered electron mode in the SEM, because that mode is sensitive to high molecular weight solids, causing mineral nanoparticles to appear extremely bright in SEM images, allowing quantification to be conducted by thresholding. A custom thresholding method was developed for the work to ensure that consistent threshold levels were used across different samples. SEM imaging, itself, proved challenging for produce surfaces, because SEM requires high vacuum, which rapidly destroys leaf cell structure. The damaged cell structure has sharp edges in images which appear bright and obscure nanoparticles. For this work, a combination of low vacuum and extremely short working time was found to allow high quality images to be acquired. Experiments involved placing a known quantity of nanoparticle suspension on two parts of a single leaf, allowing it to dry, and then conducting a controlled washing procedure on one. Tens of separate leaves were analyzed for each set of conditions to determine composite values corresponding to before and after rinsing. Analyses included both the total area attributable to nanoparticles, as well as the sizes of nanoparticle clusters. The results of the work found that for high concentration nanoparticle suspensions, a substantial fraction was rinsed off, regardless of the surface (fresh, rotten), or the solution conditions. This was likely at least in part because nanoparticles were being released from clusters where they were largely interacting with other nanoparticles, not the underlying surface. In contrast, at low nanoparticle concentrations, almost no removal was observed, regardless of solution conditions. I.e., even if solution conditions should have favored removal, the nanoparticles remained attached to the spinach surfaces. It should be noted that measurements with EPS and rotten spinach were only possible at high nanoparticle concentrations because of substantial background artifacts that interfered with imaging. Note, however, that removal of some EPS itself after rinsing was apparent in images, so nanoparticles attached to EPS would likely be released from surfaces with the EPS, even under conditions where release did not occur from fresh spinach.
Publications
- Type:
Theses/Dissertations
Status:
Published
Year Published:
2024
Citation:
Bezdek, Jack. QUANTIFYING NANOPARTICLE ATTACHMENT TO PRODUCE SURFACES. Thesis, University of Oklahoma, 2024.
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Progress 04/01/22 to 03/31/23
Outputs
Target Audience:Efforts in this project year have focused on reaching other scientists studying nanoparticle attachment and release in agricultural systems. Efforts included presentation of ongoing work at scientific meetings. Changes/Problems:As described previously, the pandemic delayed initial progress on this project. We are currently in a one-year no-cost-extension period, but as of this project year have been making steady progress towards completion of the project objectives. While we unfortunately lost one of our two graduate students to another program at the end of 2021, we hired a new Master's student who started Summer 2022. What opportunities for training and professional development has the project provided?We have been working closely with the students hired for the project to help them learn laboratory techniques needed to conduct the work, as well as to help them obtain the fundamental background to understand the work. How have the results been disseminated to communities of interest?Presentations based on the results to date were made at two different scientific meetings during this project year. Details are given in the Products section. What do you plan to do during the next reporting period to accomplish the goals?In the next reporting period, we plan to conduct additional imagine experiments to study nanoparticle washing/detachment from produce surfaces, both in the presence and absence of spoilage bacteria. The work will continue the work presented at AGU, and is being designed to form the basis of a journal publication to be submitted in the current project year.
Impacts
What was accomplished under these goals?
Because the start of this two-year project (4/1/2020) coincided with the start of the pandemic, work on the project did not begin until late Fall 2020, and the pace ramped up into 2021, near the start of the previous (second) project year. By of the end of Summer 2021 (during the previous (second) project year), the project was staffed, and was beginning to make significant progress towards the project objectives, although staffing challenges persisted until 2022. At the time of this writing, two MS students and one undergraduate are currently working on the project, and the MS students are expected to complete their work, one in 2022, the second in mid-2023. Produce studied to date have included iceberg lettuce and spinach, with emphasis on spinach. Nanoparticles have included titanium dioxide (TiO2), silver (Ag), and zinc oxide (ZnO). Additional produce and nanoparticles will be added as needed to test hypotheses that emerge from ongoing work. Work to date has focused on three key areas: Experimental procedure development, SEM imaging, and determination of thermodynamic parameters for extended DLVO calculations. Experimental procedure development included working to develop controlled, reproducible procedures for damaging produce, inducing spoilage (to allow measurement of thermodynamic parameters of, and nanoparticle attachment to surface biofilms), and introducing known quantities of nanoparticles to produce surfaces. Tested methods have included both spraying and submerging in nanoparticle suspensions. Work involving determination of thermodynamic parameters for xDLVO calculations has focused on obtaining Lifshitz-van der Waals and Lewis acid-base surface energy components for produce surfaces (both in the presence and absence of biofilms) by measuring contact angles with multiple polar and nonpolar fluids with known energies, as a first step towards being able to calculate net interaction forces between surfaces and nanoparticles. One challenge with this work comes from the roughness of produce surfaces and interference from leaf veins, which cause drop pinning, an artifact that can influence the relationship between surface energy and contact angle, inducing large standard deviations in measured values. Furthermore, the presence of biosurfactants and other extracellular polymeric substances on spoiled produce reduces the surface energy of water, an effect that complicates its use for xDLVO measurements. Obtaining reproducible measurements has required rethinking our approach for these surfaces, and also writing some project-specific laboratory software to collect and process images. We have now refined our procedures and have obtained final thermodynamic parameters for many of the systems of interest, including isolated spoilage bacteria grown in the lab. Imaging initially focused on optimizing imaging modes and procedures to allow quantification of attached nanoparticles. Imaging work has made use of a newly-acquired Field-emission Environmental Scanning Electron Microscope (FE-ESEM) which allows low-vacuum imaging to be conducted. In the past year we were able to identify a set of experimental procedures that allow imaging of produce surfaces to quantify attached nanoparticles of with a range of different properties. The method makes use of high-contrast backscattered imaging for identification and quantification for nanoparticles based on heavier elements. Two different computational strategies have been tested for quantifying nanoparticle coverage. Results with an initial set of systems was presented at the 2022 American Geophysical Union (AGU) Fall Meeting, and will form the starting point for a journal publication.
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2022
Citation:
Tohren C. G. Kibbey, Keith A. Strevett. Elucidating the Role of Extracellular Polymeric Substances in Nanoparticle Attachment to/Detachment from Produce Surfaces. Nanoscale Science and Engineering for Agriculture and Food Systems, Gordon Research Conference, June 19 - 24, 2022, Southern New Hampshire University
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2022
Citation:
Jack E. Bezdek, Elina Avila, Nour Alfailakawi, Keith A. Strevett and Tohren C. G. Kibbey. Studying Nanoparticle Detachment From Biological Surfaces Using SEM Imaging. AGU Fall Meeting, Dec. 5-16, 2022, Chicago, Illinois.
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Progress 04/01/21 to 03/31/22
Outputs
Target Audience:
Nothing Reported
Changes/Problems:As described previously, the pandemic delayed initial progress on this project. We are currently in a one-year no-cost-extension period, but as of this project year have been making steady progress towards completion of the project objectives. While we unfortunately lost one of our two graduate students to another program at the end of 2021, we have hired a new Master's student who will start this summer. At present, we anticipate that we will request one additional short no-cost extension at the end of this project year to allow that student to complete his thesis based on the project, and to allow us to complete the objectives of the project. What opportunities for training and professional development has the project provided?We have been working closely with the students hired for the project to help them learn laboratory techniques needed to conduct the work, as well as to help them obtain the fundamental background to understand the work. How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?In the next reporting period, we plan to conduct a large number of measurements to determine thermodynamic parameters describing attachment of nanoparticles to produce surfaces, including contact-angle-based measurements, as well as zeta potential measurements. We will also conduct more SEM imaging experiments to explore the retention of nanoparticles by produce surfaces following washing under different conditions, and begin to relate the observations to the measured energy parameters.
Impacts
What was accomplished under these goals?
Because the start of this two-year project (4/1/2020) coincided with the start of the pandemic, work on the project did not begin until late Fall 2020, and the pace ramped up into 2021, near the start of this current (second) project year. As of the end of Summer 2021 (during the current (second) project year), the project was staffed, and was beginning to make significant progress towards the project objectives. Produce studied to date have included iceberg lettuce and spinach, with emphasis on spinach. Nanoparticles have included titanium dioxide (TiO2) and silver (Ag). Additional produce and nanoparticles will be added once preliminary thermodynamic measurements are available to guide subsequent work. Work to date has focused on three key areas: Experimental procedure development, preliminary SEM imaging, and preliminary determination of thermodynamic parameters for extended DLVO calculations. Experimental procedure development has included working to develop controlled, reproducible procedures for damaging produce, inducing spoilage (to allow measurement of thermodynamic parameters of, and nanoparticle attachment to surface biofilms), and introducing known quantities of nanoparticles to produce surfaces. Tested methods have included both spraying and submerging in nanoparticle suspensions. Preliminary imaging to date has focused on optimizing imaging modes and procedures to allow quantification of attached nanoparticles. Work to date has been done on a newly-acquired Field-emission Environmental Scanning Electron Microscope (FE-ESEM) which allows low-vacuum imaging to be conducted. The intent is to use a combination of energy dispersive X-ray spectroscopic (EDS) mapping and high contrast backscattered imaging (for nanoparticles based on heavier elements) for identification and quantification. Early work suggests that the higher-vacuum modes with sputtering of surfaces may be necessary for quantification, although low-vacuum environmental modes are still being explored. Preliminary determination of thermodynamic parameters for xDLVO calculations has so far focused on obtaining Lifshitz-van der Waals and Lewis acid-base surface energy components for produce surfaces (both in the presence and absence of biofilms) by measuring contact angles with multiple polar and nonpolar fluids with known energies, as a first step towards being able to calculate net interaction forces between surfaces and nanoparticles. One challenge with this work comes from the roughness of produce surfaces and interference from leaf veins, which cause drop pinning, an artifact that can influence the relationship between surface energy and contact angle, inducing large standard deviations in measured values. Furthermore, the presence of biosurfactants and other extracellular polymeric substances on spoiled produce reduces the surface energy of water, an effect that complicates its use for xDLVO measurements. Obtaining reproducible measurements has required rethinking our approach for these surfaces, and also writing some project-specific laboratory software to collect and process images. In parallel with this work, we have also been isolating and growing spoilage bacteria from the studied produce for surface energy measurements.
Publications
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Progress 04/01/20 to 03/31/21
Outputs
Target Audience:
Nothing Reported
Changes/Problems:Due to the pandemic and the timing of the project start, we were not able to begin work on the project until late Fall 2020. The project was Awarded April 1, 2020, just after the University had closed down all in-person research to slow the spread of the virus. Because of uncertainty about when research would be allowed to start again, combined with a sudden drop in graduate school applications, we were unable to immediately hire a student to work on the project or conduct laboratory experiments related to the project. As a result of this delay, we will definitely request a no cost extension to the project to allow our newly-recruited student to complete his graduate work, and to allow us to complete the work proposed for the project. What opportunities for training and professional development has the project provided?We have been working closely with the new student hired for the project to help him learn laboratory techniques needed to conduct the work, as well as to help him obtain the fundamental background to understand the work. How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?In the next reporting period, we plan to conduct a large number of measurements to determine thermodynamic parameters describing attachment of nanoparticles to produce surfaces. Preliminary direct imaging experiments will also be conducted.
Impacts
What was accomplished under these goals?
Due to the pandemic and the timing of the project start, we were not able to begin work on the project until late Fall 2020. The project was Awarded April 1, 2020, just after the University had closed down all in-person research to slow the spread of the virus. Because of uncertainty about when research would be allowed to start again, combined with a sudden drop in graduate school applications, we were unable to immediately hire a student to work on the project or conduct laboratory experiments related to the project. Fortunately, in late 2020 we were able to recruit an undergraduate accelerated Master's student. The student is in his final semester of his undergraduate studies, after which he will continue as a graduate student. This project will be the basis for his thesis work. Since starting laboratory research in late 2020, we have begun conducting preliminary measurements. To date, we have focused on refining techniques and ensuring reproducibility in our measurements, but have been ramping up rapidly, and anticipate significant progress in the remainder of this project year and in the next project year.
Publications
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