Size-Dependent
Property and Cell Labeling of Semiconducting
Polymer Dots
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Abstract
Semiconducting polymer dots (Pdots)
represent a new class of fluorescent
nanoparticles for biological applications. In this study, we investigated
their size-dependent fluorescence and cellular labeling properties.
We demonstrate that the polymer conformation in solution phase largely
affects the polymer folding and packing during the nanoparticle preparation
process, resulting in solution-phase control over the fluorescence
properties of semiconducting polymer nanoparticles. The resulting
Pdots exhibit apparent size dependent absorption and emission, a characteristic
feature of different chain packing behaviors due to the preparation
conditions. Single-particle fluorescence imaging was employed to perform
a side-by-side comparison on the Pdot brightness, indicating a quadratic
dependence of single-particle brightness on particle size. Upon introducing
a positively charged dye Nile blue, all the three type of Pdots were
quenched very efficiently (<i>K</i><sub>sv</sub> > 1
×
10<sup>7</sup> M<sup>–1</sup>) in an applied quenching process
at low dye concentrations, but exhibit apparent difference in quenching
efficiency with increasing dye concentration. Furthermore, Pdots of
different sizes were used for cell uptake and cellular labeling involving
biotin–streptavidin interactions. Fluorescence imaging together
with flow cytometry studies clearly showed size dependent labeling
brightness. Small-sized Pdots appear to be more effective for immunolabeling
of cell surface, whereas medium-sized Pdots exhibit the highest uptake
efficiency. This study provides a concrete guidance for selecting
appropriate particle size for biological imaging and sensing applications