Controllable Synthesis And Multicolor Tuning Of Dye-Doped Silica Nanoparticles

Dye doped silica nanoparticles have a high photostability, less prone to photodegradation or photobleaching phenomenon, the surface of the silica has good biocompatibility and easy to modify a variety of functional groups. Therefore, the dye-doped silica nanoparticles are widely applied in the field of biotechnology.The development of dye-doped silica nanoparticles starts very early. In 1992, Van Blaaderen et al. incorporated the fluorescein isothiocyanate (FITC) into silica matrix by using a silane coupling agent (APS) with a modified Stober method. From then on. many works about the dye-doped silica nanoparticles have been reported. In 1993, Arriagade group incorporated the hydrophobic dye into the silica particles with a reverse microemulsion method, and in 2005, Zeev Rosenzweig et al successfully introduced the positive dye into the silica matrix by a simple electrostatical effect. So far, most of the organic dye can be doped into the silica particles with different ways. Moreover, with the need to decipher many biological events simultaneously, multiplexed fluorescent tags were required. Multi-color dye-doped silica nanoparticles research has been greatly developed, such as Tan et al. incorporate three dyes which have matching spectra into a silica nanoparticles at the same time, the three dyes in the silica can undergo a energy transfer by excited with a single wavelength, and the particles was used as biological markers for biolabeling. However, the current system of dye-doped silica nanoparticles still have many problems, such as the doping efficiency of many dye molecules is very low during the process of incorporating to the silica matrix, especially through the amine reactive dyes, such as FITC and silica Only 10% of the doping efficiency, which is not conducive to control the dye amount in the silica particles, but also a great waste of dye resources. Second, the dye-doped silica nanoparticles have not completely eliminated the effect on the optical properties from the external environment (for example, polar solvents or oxygen in the air). Solvent molecules can penetrate into the internal particles thought the porous structure of silica, and by the interaction between the solvent and dye molecules, the luminescent properties of particles were affected seriously. There are also many issues to be addressed for Multi-color dye-doped silica nanoparticles. First of all, multi-color dye-doped silica particles face the same problems with a single species of dye-doped particles, such as low doping efficiency, effect of the solvent and so on. In addition, the multi-color dye-doped particles also face some other problem. Currently, a conventional strategy to develop the multicolor silica particles which can be excited by a single wavelength is to combine two or more dyes which can undergo Forster resonance energy transfer (FRET) into one silica particle. Under illumination, one dye which is excited acts as donor to transfer energy for subsequent excitation of other dye (acceptor). Multicolor luminescent silica particles were acquirable by changing the ratio and thus the FRET efficiency between the donor and acceptor. It is known that the efficiency of FRET is related to the dipole-dipole coupling between the donor and acceptor. As a result, to fabricate multicolor silica particles based on FRET, it is vitally important to have control over the location and distance between the dyes in each silica particle.This paper first focus on the basic problems of dye doped silica nanoparticles from the improving the doping efficiency of amino-reactive dyes (mainly FITC). In this work, we successfully encapsulate the amine reactive dye FITC in to silica particles efficiently by using a pre-hydrolyzed method. FITC was first grafted on a silica sphere surface, and by introducing such SiO2-FITC into Stober process at appropriate time, the oligomers and primary particles which hydrolyzed from TEOS can quickly aggregate with the SiO2-FITC, thus suppressing the breaking off of FITC from the silica matrix effectively and allowing the synthesis of SiO2-FITC-SiO2 composite nanoparticles with defined structure by further deposition of silica layer. Particles synthesized by this way have more uniform dye distribution and effective protect from silica layer, the fluorescent properties and stability was also improved. Next. Dense-liquid treatment was used to improve the property of Ru (phen)32+ doped nanoparticles by decreases the solvent molecules penetrate into the silicon matrix. We also studied protection effect of different thickness in various solvents with different polarity. The first two chapters were based on the above.In Chapter 3, we reported the fabrication of multicolor silica particles from two dyes which we used in the first two chapters, fluorescent (fluorescein isothiocyanate. FITC) and phosphorescent (tris(1,10-phenanathroline) ruthenium ion, Ru(phen)32+). FITC and Ru(phen)32+ showed emission maxima at 525 nm and 585 nm respectively in solution. However, the two dyes had large overlapping region in their absorption spectra around 450 nm. Their common absorbance features and different emission colors made it possible to fabricate multicolor silica particles which can be excited by a single excitation wavelength. Multicolor character of such silica particles is attributed to the superposition of the two dyes'emissions based on the trichromatic theory of color vision. It is expected that the color of the silica particles are insensitive to the location and distance between the two dyes since they could be excited by light with the same wavelength and there is no effective overlapping between the emission of FITC and absorption of Ru(phen)32+In chapter 4, we explored the feasibility of such FITC and Ru(phen)32+ co-doped silica particles as visualized pH indicator, in which the green FITC was used as the pH sensitive dye and the red Ru(phen)32+ was employed as reference dye. It is expected that the particles may present different colors under different pH since the emission intensity of FITC was sensitive to pH. Experimental results revealed that the particles showed visualized color changes from red to yellowish-green distinguishable under a 365 nm UV lamp when pH of the buffer solutions increased from 2 to 8. Specially, such ratio-metric pH indicator was very sensitive to pH around the pKa of FITC (6.4), making it potential useful for detection of intracellular pH micro-circumstance.