Fluorescent Silicon Nanoparticles For Real-Time Fluorescence Bioimaging

In recent years,researchers have developed a variety of fluorescent nanomaterials to offer aid for a range of biological and biomedical studies involving cells or living animals.Among them,small-sized fluorescent silicon nanoparticles(SiNPs)with good optical properties and favorable biocompatibility can be used as fluorescent probes for real-time fluorescence bioimaging.In this paper,we explore the real-time fluorescence bioimaging applications of fluorescent SiNPs at both in vitro and in vivo levels.The main contents are as follows:Chapter 1:We briefly describe the development and applications of silicon-based nanomaterials in the field of biological imaging,and introduce the research progress of SiNPs-based fluorescence bioimaging applications.Then,we discuss the objectives and methods of the studies in this dissertation.Chapter 2:We give characterizations of the prepared fluorescent SiNPs,and use them as tracer agents for the real-time fluorescent imaging of the superficial sentinel lymph nodes(SLN)in mouse melanoma models.The results show that fluorescent SiNPs have good photostability and dispersion stability under the in vitro simulated physiological conditions.After the peritumoral subcutaneous injection of fluorescent SiNPs,we can observe the fluorescent labeling process of the superficial SLN in real time by naked eyes under the ultraviolet A(UV-A)irradiation.The whole imaging process is simple-operation,the only instrument be required is a handheld ultraviolet lamp.Under the guidance of fluorescent signals,we can also completely remove the SiNPs-labeled SLN.Tissue section analyses of the excised SLN confirm that the tumor metastasis has occurred in fluorescently labeled SLN.Compared with indocyanine green(ICG),a kind of SLN fluorescent tracer agent which is commonly used in clinical,fluorescent SiNPs show faster lymphatic diffusion rate and can also be absorbed by lymphatic system more easily.In addition,we study the biodistribution and metabolism of fluorescent SiNPs in mice and find that the SiNPs with hypodermic injection could be degraded and metabolized out of the body within 24 h,and they would not cause adverse effects on main organs of mice within 14 days after injection.At the same time,fluorescent SiNPs will not cause inflammation and necrosis of the skin at injection site or leave blots on skin which would be difficult to remove.Finally,we summarize the advantages and disadvantages of fluorescent SiNPs compared with the common SLN tracer agents(e.g.methylene blue dye and ICG).Chapter 3:The development,characterization and transfection efficiency of protamine sulfate(PS)-decorated SiNPs(PS@SiNPs)loaded with plasmid DNA(pDNA)(PS@SiNPs-pDNA).The pDNA are adsorbed by PS@SiNPs through the electrostatic action.It is found that this kind of gene carrier could not only deliver the adsorbed pDNA into cells to achieve the intracellular transfection of exogenous genes,but also protect pDNA from the influence of multiple physiological environments and deoxyribonuclease I(DNase I).Next,taking advantage of the good optical properties of fluorescent SiNPs,we prove the lysosomal escape function of PS@SiNPs-pDNA by analyzing the subcellular distribution of the gene carrier at different time points after co-incubation.Finally,during the long-term(25 min)and real-time fluorescence imaging of the cells incubated with PS@SiNPs-pDNA,we observe the complete dynamic process of gene carrier entering the cell nucleus by tracking the optical signals of fluorescent SiNPs.To sum up,we first investigate the capability of fluorescent SiNPs for the real-time fluorescence labeling of SLN in tumor models,and develop them into a convenient tool for SLN real-time fluorescence imaging.And then,we carry out the real-time fluorescence tracing for the cell transfection process of fluorescent SiNPs-based gene vectors.The above research findings have positive significance for further promoting the applications of silicon-based nanomaterials in the field of fluorescence bioimaging.