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Design of Optoelectronic Nose based on Core-Shell Plasmonic Nanostructure for Visual Detection and Discrimination of Environmental Pollutants

Feyzollahi, Zeynab | 2025

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 58538 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Hormozi Nezhad, Mohammad Reza
  7. Abstract:
  8. The unique optical properties of gold nanorods (AuNRs), arising from their anisotropic structure, have made them a subject of great interest across diverse applications. AuNRs exhibits two distinct localized surface plasmon resonance (LSPR), that, the color variation of AuNRs is primarily attributed to the dependence of their longitudinal LSPR peak on their aspect ratio; even minor shifts in the longitudinal position can lead to significant color changes. This high sensitivity and broad spectral tunability render AuNRs ideal candidates for the design of highly accurate and visually discernible colorimetric sensors. This study explores the design and development of colorimetric sensors based on gold nanorods for the detection and quantification of various anions in biological and environmental samples and total antioxidant in saliva. In the first section, a colorimetric sensor array composed of AuNRs was designed for the identification and discrimination of halide anions. Due to their nature, halides are considered critical environmental pollutants, making their precise monitoring in water sources particularly important. In this work, the sensor array was developed based on silver metallization on AuNRs (AuNRs@Ag). The redox properties, formation constants, and solubility differences of halide anions in their interactions with silver ions (Ag⁺) led to variations in the silver layer thickness on AuNRs. Consequently, a blue shift in the LSPR peak and a visible color change from red to green, blue, and purple occurred. These colorimetric changes enabled the identification and differentiation of various halide species. To analyze the spectral data, machine learning algorithms including linear discriminant analysis (LDA) and partial least squares regression (PLS) were employed. The results demonstrated linear responses across broad concentration ranges for F⁻, Cl⁻, Br⁻, and I⁻, with detection ranges of 40–250, 130–8000, 40–2000, and 10–1000 µM, respectively, and limits of detection (LOD) of 36.8, 122.4, 30.33, and 15.8 µM. These findings highlight the high performance of the developed colorimetric array sensor for the rapid and accurate monitoring of halide anions in aqueous sources, suggesting its potential use in environmental monitoring and water quality control. In the second part of the study, an innovative colorimetric sensor was developed for the detection and quantification of SCN⁻ and OSCN⁻ in saliva samples. These anions play key roles in the innate immune system and are involved in antimicrobial processes in saliva and other bodily fluids. A silver-coated AuNR-based colorimetric probe was designed to detect and quantify SCN⁻ and OSCN⁻, leveraging their differing interactions with silver ions to induce distinct, visually observable color changes. Furthermore, LDA and PLSR analyses enabled the accurate detection and quantification of these anions even in complex biological matrices such as saliva. The method achieved detection limits of 1.01 µM for SCN⁻ and 1.11 µM for OSCN⁻, indicating high sensitivity and precision for rapid detection in biological samples. Overall, the findings of this study underscore the high potential of metal nanostructure-based colorimetric sensors for anion analysis in biological and environmental settings. The proposed methods not only offer high sensitivity and selectivity but are also simple to use, rapid, and do not require complex instrumentation, making them promising tools for environmental surveillance and clinical diagnostics. In the third section, a novel approach was developed for assessing total antioxidant capacity (TAC) in biological samples based on the etching of AuNRs by NBS. Antioxidants play a crucial role in neutralizing free radicals and protecting cells against oxidative damage. Salivary antioxidant levels are highly correlated with blood plasma and can serve as a non-invasive marker of overall health status. In this study, a multicolor colorimetric probe was developed to visually differentiate and monitor TAC in saliva, utilizing the spectral responses of plasmonic nanostructures. LDA and PLSR techniques were combined for data analysis. The sensor exhibited linear responses in the ranges of 3.1–60.0, 2.6–60.0, 1.2–20.0, 0.8–20.0, and 0.7–14.0 µM for AA, CYS, GSH, UA, and TAC, respectively, with corresponding LODs of 1.1, 0.9, 0.4, 0.3, and 0.2 µM. The method’s accuracy and efficacy were validated using real saliva samples, confirming that this colorimetric probe offers a rapid, cost-effective, non-toxic, and minimally invasive approach for TAC monitoring with potential clinical diagnostic applications
  9. Keywords:
  10. Colorimetric Sensor Array ; Nanorod ; Etching ; Halide Anions ; Thiocyanate ; Water Analysis ; Core-Shell Nanostructure ; Gold Nanorods ; N-Bromosuccinimide ; Total Antioxidant Capacity (TAC)

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