The Design And Application Of Gold-Banomaterial-Based Optical Sensing Methods In Environmental And Biological Analysis

With the continuous development of industry, the severity of the environmental pollution has threatened the ecological balance and human’s health. As a results, it has become one of the research hotspots to design and develop the simple, rapid and sensitive measurement techniques for the detection of environmental pollutants and disease-related biomolecules. In recent decades, the emergence and usage of nanomaterials play significant roles in promoting the development of detection technology. Due to the unique optical properties, gold nanomaterials can be used as the units of signal transmission in the design of optical sensing methods. When combining ligands and chemical/biological reactions with the function of specific recognition, the detection of target molecules could be achieved with high sensitivity and selectivity. Accordingly, we developed a series of optical sensing methods based on the use of gold nanomaterials for the detection of heavy metal ions, anions, and disease-related biomolecules, and their application in the actual sample were also be employed. The detail contents of this thesis are as follows: 1. Colorimetric detection of organic mercury based on anti-aggregation of gold nanoparticles.In this work, we used gold nanoparticles as the the unit of signal transmission, and took advantage of color change based on the distance change between nanoparticles to realize the detection of organic mercury. When introduced 1-(2-pyridylazo)-2-naphthol(PAN), the monodisperse gold nanoparticles became aggregated, along with the color change from red to blue. However, due to the prior coordination between organic mercury and PAN, the aggregation of gold nanoparticles was inhibited and the color of solution was still keeping red. According to this phenomenon, a “blue to red” colorimetric assay was developed for the determination of organic mercury, and the proposed method showed high sensitivity and selectivity with the assistance of ethylenediaminetetraacetic acid disodium salt(EDTA). 2. Label-free colorimetric sensing of Cu2+ based on accelerating decomposition of H2O2 using gold nanorods as an indicator.In this work, a novel label-free colorimetric strategy was reported for sensitive detection of Cu2+ by using the morphology transition of gold nanorods. H2O2 was employed as the oxidant for corrosion of gold nanorods, leading to the decrease of aspect ratio of gold nanorods and a distinct color change from bluish green to purplish red. By virtue of the strong and specific catalysis of Cu2+ to the decomposition of H2O2, the rate of redox corrosion can be decelerated. Based on this sensing strategy, we developed a colorimetric method for the detection of Cu2+. The proposed colorimetric sensor showed sensitive and selective response toward Cu2+ without any other labelling or modification steps, and it has been successfully applied to detect Cu2+ in shellfish samples. 3. Horseradish peroxidase(HRP) assisted colorimetric detection of I- based on the morphology transition of gold nanorods.In this work, we utilized the color change of gold nanorods to design a colorimetric sensor for the detection of I-. In the presence of HRP, I- could be oxidized to I2 by H2O2, which could cause the etching of cetyltrimethyl ammonium bromide stabilized gold nanorods and lead to a blue shift of the longitudinal surface plasma resonance absorption peak and a color change from bluish green to purplish red. As a result, a label-free colorimetric method for the detection of I- based on the morphology transition of gold nanorods was established. The designed method was simple, rapid and sensitive, and showed ability of specific recognition toward I-. Moreover, satisfactory results were obtained when detecting I- in real water sample. 4. Highly sensitive fluorescent detection of Cu2+ based on fluorescein isothiocyanate functionalized gold nanoparticlesIn this work, an innovative fluorescence method for sensitive detection of Cu2+ was developed based on fluorescein isothiocyanate functionalized gold nanoparticles(FITC-Au NPs). Due to the strong binding affinity of isothiocyanate functional group to gold, FITC molecules could adsorb on the surfaces of Au NPs, forming a simple fluorescence resonance energy transfer(FRET) system, and the fluorescence intensity of FITC was remarkably quenched. Upon adding cysteine, FITC could be displaced from the surfaces of Au NPs because the formation constant(Kf) of Au-S linkage(Kf(AuS-)=4×1035) was much higher than Au-SCN linkage(Kf(Au(SCN)2-)=1023), leading to the recovery of fluorescence intensity. However, Cu2+ could catalyze O2 to oxidize cysteine, and the generated disulfide cystine could not remove FITC from Au NPs’ surfaces. Therefore, the recovery of fluorescence intensity was much weaker when compared with that in the absence of Cu2+. Based on this strategy, the concentration of Cu2+ could be detected quantitatively. Under optimal conditions, our method exhibited high selectivity toward Cu2+ and provided a good linear relationship in the range of 1.0–17.0 nM with the detection limit of 0.37 nM calculated by 3σ/S. 5. Naked-eye sensitive ELISA-like assay based on gold-enhanced peroxidase-like immunogold activity.Gold nanoparticles have been mostly chosen as signal-producing tags to develop sensitive molecule-recognition-based immunoassays in the past decades, however, the relatively low peroxidase-like activity of gold nanoparticles could be almost inhibited when modified with proteins. In order to solve this problem, in this work, we added gold growth solution to cause the continuous enlargement of the immobilized gold nanoparticles, and the occurrence of new shell recovered their peroxidase-like activity evaluated by the catalytic oxidation of peroxidase enzyme substrate 3,3’,5,5’-tetramethylbenzidine(TMB) which could produce a bright blue color in the presence of H2O2. Under the optimal reaction conditions, the colorimetric immunoassay presented a good linear relationship in the range of 0.7–100 ng/m L and the limit of detection of 0.3 ng/m L calculated by 3σ/S for Human IgG detection. Furthermore, the developed colorimetric immunoassay was successfully applied to determinate Human IgG in diluted human serum and fetal bovine serum samples, and predicted the broad prospect for the wide use of peroxidase-like activity involved nanomaterials in bioassay and diagnostics.