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Optical Sensor Arrays Based on Nanostructured Materials for Quantitative Detection and Qualitative Discrimination of Pesticides and Structural Isomers

Fahimi-Kashani, Nafiseh | 2018

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 51397 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Hormozi-Nezhad, Mohammad Reza
  7. Abstract:
  8. There is a growing interest in developing high-performance sensors monitoring organophosphate pesticides, primarily due to their broad usage and harmful effects on mammals. In the first part of this research, by introducing conditional sensor elements (CSE), a colorimetric sensor array has been proposed for the detection and discrimination of several organophosphate pesticides (OPs). citrate-capped 13 nm gold nanoparticles (AuNPs) at nine different pH/ionic strengths were employed as simple plasmonic sensing elements in the development of a colorimetric sensor array for the detection and discrimination of five organophosphate pesticides, including azinphos-methyl (AM), chlorpyrifos (CP), fenamiphos (FP), pirimiphos-methyl (PM) and phosalone (PS), at concentration ranges of 120-400 ng. mL-1. The variety of functional groups in OP structures leads to aggregation of AuNPs. On the other hand, the aggregation behavior of AuNPs against OPs are completely different at different pH and ionic strength media. The aggregation induced spectral changes of AuNPs upon OP addition has been analyzed with pattern recognition techniques, including hierarchical cluster analysis (HCA) and linear discriminant analysis (LDA). The proposed colorimetric array could efficiently discriminate among individual OPs and their mixtures. Finally, it was found that the sensor array can detect various OPs in real samples, successfully.Most array-based sensing platforms, to date, utilize static response patterns for discrimination of a wide variety of analytes, but only a few studies have focused on the important task of quantitatively resolving structural isomers, which are nowadays important because of their broad usage in medicines and industries. A possible way of accomplishing this feat is to combine kinetic (rather than static) sensor response profiles with the chemical tongue strategy to allow the development of arraybased sensors for isomeric discrimination. In the second part of this research, by adding the time dimension, a simple and novel gold nanorod (AuNR)-based chrono-colorimetric sensor array is proposed for chemical discrimination applications. Because of their similar structure but different redox potentials, dihydroxybenzene (DHB) structural isomers have been chosen, as models, to evaluate the applicability of the proposed array. The principle of the array relies on various growth rates of silver shells on AuNRs at different silver ion/ AuNR concentration ratios owing to the different kinetic behaviors of DHBs, which can be used as fingerprints to identify DHBs with the help of multivariate analysis methods. The combinatorial colorimetric response of AuNRs upon DHB addition has been analyzed by linear discriminant analysis and hierarchical cluster analysis. Finally, identification of individual DHBs or their mixtures in real samples confirms the potential application of the proposed array.In the third part of this study, a reliable, simple, and sensitive fluorescence method was developed for the determination of methyl parathion (MP) in rice using MoS2 Quantum Dots (QDs). Rapid hydrolysis of MP under alkaline condition and thus formation of p-nitrophenol (p-NP) can be used for MP detection. The functional mechanism of the nanoprobe relies on p-nitrophenol-induced photoluminescence quenching of MoS2 QDs. The high probability of resonance energy transfer (RET) stems from the spectral overlap of MoS2 QDs emission spectra and absorption spectra of p-NP. The high value of Stern-Volmer constant (KSV=3.73× 104 M−1) suggests efficient quenching of MoS2 QDs by MP in the course of ET process. Under optimum conditions, a linear calibration curve was obtained for the range of 0.1 µg.mL-1 to 30 µg.mL-1 of MP with a detection limit as low as 0.085 µg.mL-1 (S/N=3). Furthermore, this platform allows detection of MP in rice and tap water with satisfactory results. This nanoprobe can be utilized as a new generation of Flurescent sensor elements in the array techniques
  9. Keywords:
  10. Gold Nanorods ; Conditional Sensor Elements ; Spherical Gold Nanoparticles ; Silver Nanoshell Growth ; Structural Dyhydroxy Benzen Isomers

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