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Design of Colorimetric Sensor Arrays Based on Gold Nanorods for Speciation and Discrimination of Biomolecules and Environmental Pollutants

Orouji, Afsaneh | 2023

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 56926 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Hormozinezhad, Mohammad Reza; Ghasemi, Forough
  7. Abstract:
  8. The vivid optical properties of gold nanorods (AuNRs) arising from their unique structural anisotropy have been an object of fascination in a broad range of applications over the past decade. The pseudo-one-dimensional rod-shaped morphology of AuNRs underlies two distinct LSPR bands attributed to the longitudinal and the transversal oscillation of the surface plasmons. Indeed, the brilliant and high-contrast rainbow color tonality of AuNRs primarily emanates from the dramatic dependency of the location of the aforementioned bands on the aspect ratio of the nanorods. It is so profound that a minute increment of the aspect ratio is followed by a significant redshift of the longitudinal peak along with a slight blueshift of the transversal band. Such a high sensitivity and spectral dimensionality have sculpted an exquisite candidate out of AuNRs for the design of highly accurate visual colorimetric assays with brilliant color variations. In the first part of this research, a multicolor sensor array consisting of two types of gold nanostructures (i.e., gold nanorods (AuNRs) and gold nanospheres (AuNSs)) was designed for the discrimination and determination of critical BAs (i.e., spermine (SM), tryptamine (TT), ethylenediamine (EA), tyramine (TR), spermidine (SD), and histamine (HT)). The design principle of the probe was based on the metallization of silver ions on the surface of AuNRs and AuNSs in the presence of BAs, forming Au@Ag core−shell nanoparticles. Changes in the surface composition, size, and aspect ratio of AuNSs and AuNRs induced a blue shift in the plasmonic band, which was accompanied by sharp and rainbowlike color variations in the solution. The collected data were visually assessed and statistically analyzed by various data visualization and pattern recognition methods. Namely, linear discriminant analysis (LDA) and partial least squares (PLS) regression were employed for the qualitative and quantitative determination of BAs. The responses were linearly correlated to the concentrations of BAs in a wide range of 28.4−800.0, 9.0−800.0, 20.8−800.0, 27.5−800.0, 51.9−800.0, and 45.9−800.0 μmol L−1 with the limit of detections of 9.5, 3.0, 6.9, 9.2, 17.3, and 15.3 μmol L−1 for SD, SM, TT, HT, EA, and TR, respectively. Finally, the practical applicability of the sensor array was investigated by the determination of BAs in meat and fish samples by which the potential of the probe for on-site determination of food freshness/spoilage. In the second part of this research, by using AuNRs, silver ions, and ascorbic acid, a multicolorimetric nanosensor was designed for the potential of hydrogen (pH) measurement. The reduction of silver ions by ascorbic acid, which is strongly influenced by pH, results in silver nanoshell deposition on the surface of AuNRs. Consequently, the formation of Au@Ag core-shell NRs causes a series of blue shifts in the longitudinal peaks of AuNRs and elegant color changes according to pH values ranging from 2.0 to 12.0. As a result of spectral shifting, distinct color variations were observed from brownish pink/light green color (acidic media) to dark green/blue color (neutral media) and eventually purple/brown color (basic media). Furthermore, a paper-based analytical device was introduced for on-site pH screening. The pH-sensitive a paper-based analytical device was simply fabricated by immobilizing AuNRs on the surface of filter paper. Finally, the practical applicability of the developed plasmonic probe was investigated by the pH monitoring in urine, spoiled meat, drinking water, and seawater sample. In the third part of this research, a multicolorimetric probe based on silver-deposition-induced color variations of gold nanorods (AuNRs) was designed for identification and quantification of Cr species including Cr (III) and Cr (VI) (i.e., CrO42− and Cr2O72−) in water samples. In fact, the presence of Cr species leads to inhibition of the silver metallization of AuNRs to various degrees depending on the concentration and identity of the analyte. This process is accompanied by the blue shift of the longitudinal peak which results in sharp-contrast rainbow-like color variations, thereby providing great opportunity for highly accurate visual detection. The gathered dataset was then statistically analyzed using two pattern recognition and regression machine learning techniques. Responses were linearly related to Cr species concentrations over a wide range of 37.7−1000.0, 8.7−200.0, and 2.9−200.0 μmol L−1 with detection limits of 37.7, 8.7, and 2.9 μmol L−1 for Cr3+, CrO42−, and Cr2O72−, respectively. The practical applicability of the multicolorimetric probe was evaluated by analyzing Cr species in several water specimens comprising tap water, mineral water, river water, and seawater. In the fourth part of this research, the outstanding potentials of two inexpensive mild oxidants comprising N-bromosuccinimide (NBS) and N-chlorosuccinimide (NCS) in highly-fast and controllable etching of AuNRs at room temperature. In an attempt to elucidate the etching mechanism, the effects of various parameters including the etchant concentration, pH, as well as the kinetics of the etching process were thoroughly investigated. After all, the capability of NBS in decarboxylating the amino acids was further exploited in the design of an all-inclusive multi-colorimetric sensor array based on the etching of AuNRs for the sensitive quantification and highly-accurate discrimination of the entire 20 amino acids in the micromolar range. To this end, the acquired dataset was analyzed by two machine learning techniques including partial least square regression (PLSR) and linear discriminant analysis (LDA)
  9. Keywords:
  10. Colorimetric Sensor Array ; Gold Nanorods ; Etching ; Food Spoil ; Speciation ; Amino Acid ; Core-Shell Structure ; PH Monitoring ; Environmental Pollutant

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