Study On The Synthesis And Appication Of QD@SiO₂ Fluorescent Probes

Fluorescent probes have several advantages such as high sensitivity, good selectivity, simple and low cost, promoting their applications in biomedical research. Due the unique photophysical properties, such as broad-band absorption, size-dependent narrow-band emission, and resistance to photobleaching, the quantum dots (QDs) based fluorescent probes for biomedical research have become hot in recent years. Coating QDs with silica shells, the stability and biocompatibility of QDs-based fluorescent probes have been improved and the surface of the silica can be easy modified, thus their application in biomedical research. In this paper, two dual-emssion QD@SiO2 fluorescent probes have been designed to realize the ratiometric detection of Zn2+ and the simultaneous detection of Zn2+ and Cd2+ based on different mechanisms. The main contents are as follows:1. Different coloured-QD@Si02 are synthesized beasd on the reverse microemulsion method and the thickness of the silica shell can be controlled, thus modifying the surface of the silica with different groups. Using different assembly methods, QD@SiO2 fluorescent probes with different constructions are established.2. Two different coloured QDs and meso-tetra(4-sulfonatophenyl)porphine dihydrochloride (TSPP) are used to realize the ratiometric detection of Zn2+ based on the mechanism of fluorescence resonance energy transfer (FRET). TSPP is chosen as the recpter of Zn2+ and the FRET acceptor, assembled on the surface of silica through electrostatic interaction. Silica shells are chosen as spacers to adjust the interactions between QDs and TSPP. The chelation of Zn2+ by TSPP leads to the reverse change of the FRET efficiency between different QDs and TSPP, as well as the PL of QDs. By measuring the emission intensity ratios between the two QDs, the ratiometric sensing for Zn2+ is achieved. Due to the ratiometric detection method, the limit of detection is reduced to 50 nM, thus enhancing the selectivity and visual detection performance.3. Two different coloured QDs, TSPP and 1,10-phenanthroline (Phen) are used to creat a nanostructure to realize the simultaneous detection of Zn2+ and Cd2+ based on the FRET and photoinduced hole transfer (PHT) mechanisms respectively. TSPP is chosen as the recpter of Zn2+ and the FRET acceptor. TSPP and red QDs are assembled on the surface of green QD@SiO2 through electrostatic interaction. Phen is chosen as the recpter of Cd2+ and the PHT acceptor, assembled on the surface of red QDs through metal affinity coordination. In the presence of Zn2+, the FRET efficiency between green QDs and TSPP is reduced. In the presence of Cd2+, Phen leave the surface of red QDs breaking the PHT process. The simultaneous detection of Zn2+ and Cd2+ can be realized through the "turn-on" mode of the green and red signals respectively. The detection signals for Zn2+ and C2d+ in this probe for are non-interfering and the limit of detection are 0.3 and 0.5 μM respectively with nice visual detection performance.