Development Of New Colorimetric Sensig For Silver And Iodine Ions

In recent years, more attention has been given to colorimetric sensors based on gold nanoparticles (AuNPs) due to its advantages of good selectivity, high sensitivity and convenient detection. Furthermore, the recognition signals can be transformed into color changes which can be easily distinguished by naked eyes or observed using UV-vis absorption spectrometry without complicated instrumentations. Heavy metal exhibits serious adverse effect on human health, which is of high toxicity, chronicity and accumulation. In addition, some anions play a critical role in many chemical and biological processes, which may have a severe influence on people. Therefore, colorimetric transducers based on AuNPs provide a new way for reliable and rapid detection of toxic ions.There are three chapters in the thesis:1. The first chapter systematically introduces the definition, principle, classification, application and tendency of biosensors. Then, most attention is focused on the design of optical biosensors, the development of new nanoparticles and the application of AuNPs. Subsequently, the interaction between DNA and metal ions coupled with its application in colorimetric sensors are described. Finally, it reviews the effect of heavy metals and halogen on the human health combined with its analysis significance.2. A novel, simple, and rapid colorimetric strategy is proposed based on the aggregation of AuNPs induced by the unfolding of G-quadruplex (G4) in the presence of silver ions (Ag+). AuNPs to which compact G4structures were attached had higher stability toward salt-induced aggregation of AuNPs than those on which random coil single-stranded DNA (ssDNA) structures were anchored. In the Ag+-free system, AuNPs remained mono-dispersed. In contrast, upon addition of Ag+, the G4structure unfolded, inducing aggregation of the AuNPs. The linear range of the as-established colorimetric assay for Ag+was from2.0×10-8M to2.0×10-6M, with a detection limit of approximately7nM. Additionally, the colorimetric sensor showed good selectivity toward Ag+. The proposed method offers a new assay for metal ion-mediated aggregation-based colorimetric sensing and may pave a new way for heavy metal ions detection.3. A simple, reliable colorimetric detection method for iodide has been well-established based on the anti-aggregation effect of AuNPs in this paper. This assay is highly sensitive and selective toward iodide over other interferent anions due to the high stability of the inorganic complex formed between Hg2+and iodide. In the absence of iodide, T-rich ssDNA can specifically bind with Hg2+to form a stable T-Hg2+-T complex, inducing the solution color change from wine-red to finally violet blue with increasing concentration of Hg2+. However, when Hg2+is first treated with iodide, the T-Hg2+-T interaction will be interrupted, which results in the anti-aggregation of AuNPs. A linear response from4x10-8M to4×10-6M was obtained for iodide, and a detection limit of13nM was achieved.