Study On The Detection Of Ferric And Zinc Ion Based On Quantum Dots@Silica Fluorescent Sensors

Fluorescent sensors have several advantages such as simple, good selectivity, high sensitivity, and bw cost, showing broad application in bio medical research. The design and application of quantum dots ?QDs? based fluorescent sensors for biomedical research has become a research hotspot in recent years because QDs, a kind of novel nano fluorescent material, possess unique photophysical properties, such as narrow-band emission, broad-band absorption, size-dependent colour and resistance to photobleaching. QDs-based fluorescent sensor techniques become an important tool for analysis. Coating QDs with silica shells, the anti disturbance capability and fluorescent stability of QDs-based fluorescent sensors have been improved and the surfece of the silica can be easy modified, expanding their application in biomedical research. Iron and zinc are the most abundant transition metal elements in humans and play important roles in various biological systems. In this paper, a single emission florescent sensor and a ratio metric florescent sensor, based on QDs@SiO₂ material, have been designed to realize the fluorescent detection of Fe??? and Zn??? by fluorescence resonance energy transfer mechanism The main contents are as follows:1. Bule quantum dots capped by silica?bQDs@SiO₂? are synthesized based on the reverse microemulsion method and the thickness of the silica shell is about 5 nm. Besides, amino functional group is modified on the surface of silica by silane coupling agent. Green quantum dots capped by silica?gQDs@SiO₂? are synthesized based on the Stober method and the size of gQDs@SiO₂ is approximately 200 nm. QDs@SiO₂, as a kind of nano fluorescent materials, has excellent fluorescent performance and improved anti interference ability, laying the foundation for the construction of fluorescent sensors.2. Choosing bQDs@SiO₂ as fluorophores and meso-tetra ?4-sulfonatophenyl? porphine dihydrochloride ?TSPP? as receptor, a novel bQDs@SiO₂/TSPP nano-fluorescent sensor is constructed to realize the detection of Fe??? and Zn??? based on Forster resonance energy transfer ?FRET? mechanism. As the FRET donor, bQDs@SiO₂ was subtly selected to match the absorption spectra of TSPP, which serves as the Fe??? and Zn?II?-sensitive FRET receptor. TSPP is assembled on the surface of bQDs@SiO₂ by electrostatic association, quenching the photo luminescence ?PL? of bQDs@SiiO₂ via FRET process, The thin silica is utilized to control the distance and FRET process, and interrupt the photo-induced hole transfer ?PHT? process between bQDs@SiiO₂ and TSPP. The chelation of Fe?III? or Zn?H? leads to the reverse change of the FRET efficiency between bQDs@SiiO₂ and TSPP, as well as the PL of bQDs@SiiO₂. Using the PL of bQDs@SiO₂ as a signal, quantitative detection of Fe??? and Zn??? is realized and the limit of detection are 80 nMand 15 nM, respectively.3. Based on single emission florescent sensor system, a new type of double emission ratiometrie fluorescent sensor has been constructed by utilizing two different colored QDs@SiO₂ nano material to realize the visual detection of Fe??? and Zn???. Amino group modified bQDs@SiO₂ deposit on the surface of gQDs@SiO₂ by electrostatic adsorption. And then negative charged TSPP adsorbs on the surface of bQDs@SiO₂ by electrostatic association, assembled into ratiometrie fluorescent sensor. TSPP quenches the PL) of bQDs@SiO₂ via FRET process. The different thicknesses of silica contribute to the control of the interaction between QDs and TSPP. Because of the thick silica shell of gQDs@SiO₂, the FRET process between gQDs and bQDs is bloeked and the stability of fluorescence is promoted. TSPP can selectively complex Fe??? or Zn??? coexisting in serum samples with the addition of masking agent TPEN and oxidizing agent H2O₂, resulting in the change of the FRET efficiency between bQDs@SiO₂ and TSPP and the PL of bQDs@SiO₂. In the whole detection process, the PL of gQDs@SiO₂ remains unchanged. By measuring the emission intensity ratios between the two QDs, the ratiometric sensing for Fe??? and Zn??? is achieved. Due to the ratiometrie detection method, the limit of detection is reduced to 40 nM and 6 nM respectively. Meanwhile, the selectivity and visual detection performance are much promoted.