Progress 01/01/24 to 12/31/24

Outputs
Target Audience:The first target audience reached by our efforts during this reporting period is professional researchers working on sensor development. Our primary means of engagement with this audience is through journal publications. Additionally, we connected with this group of audiences by presenting our work at the prestigious Gordon Research Conference, showcasing our progress to the experts in the field. We also engaged with local stakeholders during the symposium between UConn and the Connecticut Agricultural Experiment Station, fostering collaboration and knowledge exchange on cutting-edge sensing technologies for agricultural applications. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Graduate students Niloofar Zolfigol (female), Chen Song (female), and Heejoeng Ryu (female) have each been assigned different tasks within this research project during this reporting period. Niloofar Zolfigol and Chen Song have been extensively trained in nanomaterial synthesis and characterization and the use of various spectroscopic methods. Niloofar Zolfigol was also well-trained in SERS-based detection. Heejeong Ryu has been well-trained in various analytical methods, including Fourier Transform Infrared Spectroscopy. All students received various training, including chemical safety training, working ethics training, and compliance training offered by UConn. Furthermore, all students have developed their oral presentation skills significantly through comprehensive training and weekly meetings with the advisors. How have the results been disseminated to communities of interest?The research findings are shared with the sensor research community through a presentation at the Nanoscale Science and Engineering for Agriculture and Food Systems Gordon Research Conference. They are also disseminated to local stakeholders through the UConn-Connecticut Agricultural Experiment Station Symposium. Additionally, publication in a peer-reviewed journal ensures effective outreach to broader scientific communities interested in pesticide detection, helping to expand the work's impact and visibility. What do you plan to do during the next reporting period to accomplish the goals?During the next reporting period, we will focus on the continued synthesis of photocrosslinkable polymers that can covalently anchor to gold surfaces for molecular imprinting, as well as the preparation of Janus particles for pesticide detection.

Impacts
What was accomplished under these goals? Developed and optimized synthesis protocols for gold nanoparticles (AuNPs), gold nanorods (AuNRs), and silver-coated gold nanorods to serve as surface-enhanced Raman scattering (SERS) substrates. These nanomaterials were thoroughly characterized for their optical and morphological properties using UV-vis spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). We successfully synthesized AuNPs using a seed-mediated process. The formation of ~40 nm particles was confirmed by a color change from dark purple to red. To grow larger particles (~120 nm), the seed solution was added to a mixture containing more gold salt and a mild reducing agent. By carefully controlling reagent amounts and reaction time, we achieved the desired size, as indicated by a visible color change. The absorbance spectra of the gold nanoparticle suspensions were collected and analyzed. To better match the absorbance wavelength with the laser source, AuNRs and silver-coated AuNRs were also synthesized. AuNRs were produced using a seed-based growth method in the presence of surfactants, while the silver-coated AuNRs were formed by depositing silver onto the AuNRs. The wavelength shifts and morphology of the nanorods were characterized using UV-vis spectroscopy, SEM, and TEM, respectively. The synthesis procedures have been standardized. All these nanoparticles are ready for surface-enhanced Raman scattering detection. Generated Raman fingerprint spectra for six target pesticides using a portable Raman spectrometer and identified characteristic peaks suitable for SERS-based detection. The six pesticides targeted in this project are analyzed using a portable Raman in the lab. In brief, the pesticide power is placed on a silica substrate under a portable Raman. The Raman spectrum of each pesticide is collected accordingly and then used to identify the characteristic peaks of each pesticide in SERS-based detection. Established procedures for SERS-based pesticide detection in both liquid (solution-based) and solid (surface-based) formats using portable Raman systems. To conduct SERS-based pesticide detection, we began by focusing on methyl parathion detection both in solution and on solid substrates. For solution-based detection, the as-synthesized nanoparticle suspension was first placed in the detection chamber of a portable Raman spectrometer to collect a baseline spectrum. Methyl parathion was then gradually added (titrated) into the nanoparticle suspension at various concentrations, and the Raman spectra were collected immediately after shaking to ensure a homogeneous mixture. We systematically studied the effects of the number of nanoparticle washes, nanoparticle concentrations, and incubation time between the pesticide and nanoparticles on the resulting SERS signals. Reliable detection of methyl parathion at micromolar levels in solution was achieved with good reproducibility, and a standardized procedure for solution-based detection was developed. In parallel, we investigated detection in the format of a solid SERS substrate. In this method, a small volume of the methyl parathion-nanoparticle mixture was dropped onto a silicon substrate, and Raman spectra were collected at intervals during the drying process. Interestingly, the SERS signal increased during drying and typically peaked just before the sample was fully dry. This may be attributed to increased nanoparticle concentration, forming more "hot spots" for SERS enhancement through more frequent collisions. Once fully dry, the signal decreased, likely because the dried layer blocked light penetration to deeper regions. This dynamic behavior suggests a new strategy for optimizing SERS detection by capturing the signal at the optimal drying stage. Successfully synthesized a photocrosslinkable coumarin-containing polymer The synthesis of the photocrosslinkable coumarin-based polymer was carried out in two main steps: preparation of a coumarin-functionalized monomer and its incorporation into a polymer backbone. First, the coumarin building block was synthesized by reacting methylcoumarin with chloroethanol in the presence of potassium carbonate, using ethanol as the solvent. The reaction was stirred overnight at 78?°C, then cooled, purified through solvent extraction and drying, and yielded a white powder with a high reaction efficiency of 90%. To make the polymer, the coumarin derivative was chemically linked to a base polymer, poly(isobutylene-alt-maleic anhydride), in dimethylformamide at 90?°C under a nitrogen atmosphere. A mixture containing the coumarin compound, phenylethyl alcohol, chloroethanol, and ethanol was added to the solution and stirred overnight. The resulting product was isolated using hexane/acetone precipitation and further purified by dialysis over two days. The final coumarin-based polymer was obtained with a conversion yield exceeding 99%. The chemical structures of both the intermediate compound and the final polymer were confirmed using proton nuclear magnetic resonance (1H NMR) spectroscopy in DMSO-d6. The spectra showed characteristic peaks matching the expected structures, confirming successful synthesis and functionalization. Given that the synthesized coumarin-based polymer is both pH-sensitive and light-sensitive, its potential application in pesticide detection is currently being evaluated. Designed and 3D-printed a customized sample holder with multiple detection wells. To minimize background Raman interference from the resin, the device was sputter-coated with a thin metal layer, significantly improving SERS signal clarity. To fabricate the proposed detection device with embedded sample wells, we first designed the layout using SolidWorks software and then produced the device using a FormLabs 3D printer. Upon testing, we found that the resin material used for printing exhibited strong Raman peaks, which could interfere with SERS signal detection. Since metals do not generate Raman signals, we sputter-coated a thin layer of Au/Pd alloy onto the surface of the device. This coating blocked direct laser contact with the resin, significantly reducing background interference and improving the accuracy and performance of SERS detection within the sample wells. To make this strategy cost-effective, a low-cost silver (or aluminum) coating is currently being considered as an alternative, and the thickness of the coating layer will be optimized. Disseminated research findings through conference presentations, symposia, and peer-reviewed journal publications, specifically targeting researchers and professionals in environmental monitoring, agriculture, and sensor development. These efforts enhanced the visibility and impact of the work by reaching key audiences who can benefit from the portable, high-sensitivity detection platform - supporting faster decision-making, improved pesticide management, and reduced risks to environmental and public health. Provided hands-on training for underrepresented STEM students in nanomaterial synthesis, spectroscopic characterization, Raman-based sensing, and device fabrication, supporting workforce development in agricultural monitoring and sensor technologies. Specifically, graduate students Niloofar Zolfigol, Chen Song, and Heejeong Ryu, all female, have been working on this project. Niloofar and Chen have received extensive training in nanomaterial synthesis, characterization, and the use of various spectroscopic techniques. Additionally, Niloofar has gained specialized expertise in SERS-based detection. Heejeong has been trained in a range of analytical techniques, including Fourier Transform Infrared Spectroscopy. All three students received training in chemical safety, research ethics, and research compliance through UConn. This project not only advances scientific innovation but also prepares a skilled and diverse workforce capable of addressing future challenges in agricultural and environmental monitoring.

Publications

• Type: Peer Reviewed Journal Articles Status: Published Year Published: 2024 Citation: Heejeong Ryu, Dorian Thompson, Lei Jin, Jie He, Yu Lei. rGO/HfO2 nanocomposite-enabled electrochemical sensor for high-performance pesticide detection. Talanta, 2025. 287 (15), 127606. https://doi.org/10.1016/j.talanta.2025.127606
• Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: Yu Lei, SERS Enabled Sensitive Detection of Pesticides, Nanoscale Science and Engineering for Agriculture and Food Systems, Gordon Research Conference, 06/23/2024-06/28/2024
• Type: Conference Papers and Presentations Status: Other Year Published: 2024 Citation: Yu Lei, (Bio)Sensors for Agriculture Applications. UConn - CT Agricultural Experiment Station Symposium, 06/04/2024