Study On Size-Dependent Property Of Semiconducting Polymer Dots

In recent years, semiconducting polymer nanoparticles have attracted considerableattention because of their outstanding characteristics as fluorescent probes. Thesenanoparticles, which primarily consist of π-conjugated polymers and are calledpolymer dots (Pdots) when they exhibit small particle size and high brightness, havebeen demonstrated in a wide range of applications, such as fluorescence imaging andbiosensing. The development of fluorescence imaging techniques has providedeffective research tools to investigate many fundamental processes in the life sciences.Recent research has demonstrated that Pdots exhibit excellent characteristics asfluorescent probes, including their extraordinary fluorescence brightness, fastemission rate, excellent photostability, non-blinking and non-toxic features. Inparticular, we recently carried out a systematic characterization of the opticalproperties and performance of Pdots as cellular labels, especially for fluorescenceimaging and flow cytometry. We found that single-particle brightness andcell-labeling brightness of Pdots are more than an order of magnitude higher thanthose of inorganic Qdots of comparable particle size. We have also developedseveral simple yet powerful approaches for introducing functional groups andcontrolling the surface chemistry of Pdots; successful functionalization is apre-requisite in employing these novel nanoprobes for cellular labelling and in vivoimaging, and as versatile biosensors. These developments have formed a newfrontier in nanobiotechnology and nanomedicine, and represent a new direction that isorthogonal to the more established areas of conjugated polymers for optoelectronicdevices and conjugated polyelectrolyte biosensors. The superior properties of Pdotsover other fluorescent probes have established their enormous potential in biology andmedicine as highly bright in vitro and in vivo probes.In this study, we investigated their size-dependent fluorescence and cellularlabeling properties. We demonstrate that the polymer conformation in solution phase largely affects the polymer folding and packing during the nanoparticlepreparation process, resulting in solution-phase control over the fluorescenceproperties of semiconducting polymer nanoparticles. The resulting Pdots exhibitapparent size dependent absorption and emission, a characteristic feature of differentchain packing behaviors due to the preparation conditions. Single-particlefluorescence imaging was employed to perform a side-by-side comparison on thePdot brightness, indicating a quadratic dependence of single-particle brightness onparticle size. Upon introducing a positively charged dye Nile blue, all the three typeof Pdots were quenched very efficiently in an applied quenching process at low dyeconcentrations, but exhibit apparent difference in quenching efficiency withincreasing dye concentration. Furthermore, Pdots of different sizes were used forcell uptake and cellular labeling involving biotin streptavidin interactions.Fluorescence imaging together with flow cytometry studies clearly showed sizedependent labeling brightness. Small-sized Pdots appear to be more effective forimmunolabeling of cell surface, whereas medium-sized Pdots exhibit the highestuptake efficiency. This study provides a concrete guidance for selecting appropriateparticle size for biological imaging and sensing applications.