The Design Of Silicon Nanoparticles, And Their Basic Applications Of Biological Fluorescence Imaging

Silicon nanomaterials are an important type of nanomaterials, exhibiting unique optical, electronic, or/and mechanical properties. The fast development of silicon nanomaterials with well-defined structures and required functionalities has vastly promoted the advancement of silicon nanotechology. Bulk silicon with an indirect band gap basically features poor optical properties. However, when the size of silicon particles is reduced to nanoscale(generally less than 5 nm), the overlap of the electron and hole wave functions is distinctly increased, leading to dramatic enhancement of recombination rates of electrons and holes. As a result, such small-sized SiNPs exhibit relatively strong fluorescence, showing the prospect of long-awaited optical applications. Therefore, intense studies have been intrigued to develop fluorescent SiNPs and their optics-relative applications since the first observation of porous silicon-based fluorescence. In the past three decades, scientists have made great strides in developing a great deal of fabrication techniques to prepare SiNPs. In recent two decades, many synthetic strategies have been developed for the preparation of SiNPs. However, effective methods for facile synthesis of water-dispersible, outstanding optical properties, and multicolor photoluminescence SiNPs are still much in demand.In this dissertation, we present new aqueous synthetic approach for facile one-pot synthesis of multicolor photoluminescence SiNPs. The as-prepared SiNPs have small size(2.0-3.5 nm) and are water dispersible, strong fluorescence(photoluminescence quantum yield(PLQY) of 20-25 %), favorable biocompatible, and superbly suitable for biological fluorescence imaging. The main results are as following:Chapter 1: In this chapter, we give an introduction to the recent research progressed of silicon nanomaterials.Chapter 2: In this chapter, we present a facile microwave-assisted strategy for preparation of biofunctional and fluorescent SiNPs by using proteins as hydrophilic. The as-prepared SiNPs show strong fluorescence(PLQY: 18%), robust photostability. Remarkably, the SiNPs feature excellent aqueous dispersibility and biospecific properties owing to a large number of protein molecules on the surface. Our experiment further demonstrates that such SiNPs could be directly employed for immunofluorescent cellular targeting, without requiring additional bioconjugation.Chapter 3: A large-scale synthetic strategy is developed for facile one-pot aqueous synthesis of silicon nanoparticles(SiNPs) yielding ~0.1 g SiNPs small sizes(~2.2 nm) in 10 min. The as-prepared SiNPs feature strong fluorescence(PLQY: 20-25%), favorable biocompatibility, and robust photo- and pH-stability. Moreover, the SiNPs are naturally water dispersible, requiring no additional post-treatment. Such SiNPs can serve as highly photostable bioprobes and are superbly suitable for long-term immunofluorescent cellular imaging.Chapter 4: we herein introduce a facile, low-cost photochemical method capable of rapid(< 40 min) and large-quantity(~10 g) production of highly-fluorescent(PLQY: 25%) silicon nanoparticles(SiNPs) of tunable optical properties(peak emission wavelength in the range of 470-560 nm) under ambient air conditions, by introducing 1,8-naphthalimide as reducing agent and surface ligands. The as-prepared SiNPs serving as photostable nanoprobes are superbly suitable for long-term cellular imaging. Our findings provide a powerful method for mild-condition and low-cost, large-quantity production of highly fluorescent and photostable SiNPs for various promising applications.In summary, this thesis illustrates a comprehensive investigation of the design of silicon nanoparticles and their basic applications of biological fluorescence imaging. These remarkable research results make them as a new avenue towards optical applications, including biological fluorescence imaging, light-emitting diodes(LED), and leading to a promising perspective of long-awaited silicon nanomaterials.