Design Of Gold Nanoparticle-based Colorimetric Sensing Assays For Sensitive And Selective Sensing Of Trace UO₂²⁺

In recent years, gold nanoparticles(AuNPs) have drawn considerable research attention in the fields of catalysis, drug delivery, imaging, diagnostics, therapy and biosensors due to their unique optical and electronic properties. In this thesis, three colorimetric sensors including OPA-AuNPs, MPG-AuNPs, L-Ser-AuNPs have been prepared for colorimetric detection of U(VI). The TEM, Uv-vis, and Zeta potential have been utilized to analyze the structure of the functionalized gold nanoparticles. The factors that affect the colorimetric assay in aqueous solution such as initial pH values and contact time have been investigated by colorimetric experiments. In addition, the sensitivity and selectivity of three colorimetric sensors have also been discussed.Based on the fact that the stability constants of U(VI)-phosphoric complexes are markedly higher than those of carboxylate complexes, a simple colorimetric sensor for the detection of UO22+ was developed using o-phosphorylethanolamine functionalized gold nanoparticles. Chelation of U(VI) by several of phosphate ligands, bound to different nanoparticles, led to nanoparticle aggregation in solution. The color change induced by 2.09 μmol·L-1 UO22+ can be easily observed by naked eyes, which is particularly applicable to on-site and real-time detection. The absorbance ratio(A650/A524) was linear with the UO22+ concentration in the range of 0.7-4.16 μmol·L-1. Under optimum conditions(pH 4.0), the detection limit of UO22+ could be as low as 0.086 μmol·L-1. The proposed sensing system provided a good selectivity for UO22+.A simple colorimetric sensor for the detection of UO22+ and Cu2+ was been developed using N-(2-Mercaptopropionyl)glycine functionalized gold nanoparticles. Chelation of U(VI) by several of amino and carboxyl ligands, bound to different nanoparticles, led to nanoparticle aggregation in solution. This gave rise to a color change from winered to blue that was discernible by the naked eye. The absorbance ratio(A650/A524) was linear with the UO22+ and Cu2+ concentration in the range of 3.5-20.8 μmol·L-1 and 5.23-30.85 μmol·L-1, respectively. Under optimum conditions(pH 3.0), the detection limit of UO22+ and Cu2+ could be as low as 0.83 μmol·L-1 and 0.97 μmol·L-1, respectively. The proposed sensing system provided a good selectivity for UO22+.A simple colorimetric sensor for the detection of UO22+ was developed using L-Serine functionalized gold nanoparticles. Chelation of U(VI) by several of carboxyl ligands, bound to different nanoparticles, led to nanoparticle aggregation in solution. This gave rise to a color change from wine red to blue that was discernible by the naked eye. The absorbance ratio(A650/A524) was linear with the UO22+ concentration in the range of 23.80-88.27 μmol·L-1. Under optimum conditions(pH 4.0), the detection limit of UO22+ was 6.76 μmol·L-1. The proposed sensing system provided a good selectivity for UO22+.