Design And Biological Imaging Of Fluorescent Nanodots Based On Semiconducting Polymer

Semicinducting polymer dots (Pdots) are excellent fluorescent probes with manysuperior properties such as high brightness, fast emission rate, excellent photostability,outstanding colloidal stability and good biocompatibility. Although Pdots have beenwidely used in biological applications, they encounter challenges such as broademission spectra. The properties of Pdots can be improved by a doping or blendingstragety with functional fluorescent dyes. In the regenerative medical field,mesenchymal stem cells (MSCs) have accecpted tremendous attentions due to theirgreat potential for disease treatment. Reliable methods to image and track stem cellsin vivo are urgently required in order to verify the fate of stem cells in the targetorgans. A variety of fluorescent probes have been developed for the tracking ofMSCs. However, those probes were always limited by stabilities and safeties. Toovercome the problems, Pdots will be employed to investigate the labeling andtracking the MSCs in vitro and in vivo. The results of this dissertation can bedescribed as follows.1. We developed a ratiometric fluorescent sensor based on semiconducting polymerdots chelated with terbium ions to detect Bacillus anthracis spores in aqueoussolution. Fluorescent polyfluorene (PFO) dots serve as a scaffold to coordinatewith lanthanide ions that can be sensitized by calcium dipicolinate (CaDPA), aunique biomarker of Bacillus spores. The absorption band of PFO dots extendsto deep UV region, allowing both the reference and the sensitizer can be excitedwith a single wavelength (~275nm). The fluorescence of PFO remains constantas a reference, while the Tb3+ions exhibit enhanced luminescence upon bindingwith DPA. The sharp fluorescence peaks of-phase PFO dots and thenarrow-band emissions of Tb3+ions enable ratiometric and sensitive CaDPAdetection with linear response over nanomolar concentration and a detection limitof~0.2nM. The Pdots based sensor also show excellent selectivity to CaDPAover other aromatic ligands. Our results indicate that the Tb3+chelated Pdotssensor is promising for sensitive and rapid detection of Bacillus anthracis spores. 2. We described on a europium-complex grafted polymer for preparing stablenanoparticle probes with high luminescence brightness, narrow emissionbandwidth, and long luminescence lifetimes. A Eu complex bearing an aminogroup was used to react with a functional copolymer poly(styrene-co-maleicanhydride) by the spontaneous amidation reaction, producing the polymer graftedwith Eu complexes in the side chains. The Eu-complex grafted polymer wasfurther used to prepare Eu-complex grafted Pdots and Eu-complex blendedpoly(9-vinylcarbazole) composite Pdots, which showed improved colloidalstability as compared to those directly doped with Eu-complex molecules.The efficient cell uptake and specific cell surface labeling observed in mammaliancells suggest their potential applications in time-resolved bioassays and cellularimaging.3. We employed the highly fluorescent semiconducting polymer dots (Pdots) assuperior probes for labeling and tracking of umbilical cord stem cells. The Pdotswere conjugated to a cell penetrating peptide (R8), and the cellular uptake ofR8-Pdot bioconjugates were markedly enhanced15times than that of carboxylPdots and more than100times than that of bare Pdots. The Pdots exhibitoutstanding cell tracking capability with minimal cyto-toxicity. Fluorescentsignal from the Pdot-labeled stem cells can be detected in the17thgenerationcultured in vitro and the labeled cells can be traced for15days afterpost-transplantation in mice. Moreover, biodistribution studies demonstrate thatthe stem cells mainly accumulated in the lung, different from the distribution offree Pdots that were trapped by the reticuloendothelial system (RES). With thebright labeling, great biocompatibility, and excellent long-term tracking capability,the Pdots are promising for their applications in stem cell therapy.