Abstract
Conjugated polymer nanoparticles exhibit very interesting properties for use as bio-imaging agents. In this paper, we report the synthesis of PCDTBT (poly([9-(1’-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophene-diyl)) nanoparticles of varying sizes using the mini-emulsion and emulsion/solvent evaporation approach. The effect of the size of the particles on the optical properties is investigated using UV-Vis absorption and fluorescence emission spectroscopy. It is shown that PCDTBT nanoparticles have a fluorescence emission maximum around 710 nm, within the biological near-infrared “optical window”. The photoluminescence quantum yield shows a characteristic trend as a function of size. The particles are not cytotoxic and are taken up successfully by human lung cancer carcinoma A549 cells. Irrespective of the size, all particles show excellent fluorescent brightness for bioimaging. The fidelity of the particles as fluorescent probes to study particle dynamics in situ is shown as a proof of concept by performing raster image correlation spectroscopy. Combined, these results show that PCDTBT is an excellent candidate to serve as a fluorescent probe for near-infrared bio-imaging.
Highlights
Over the past decade, conjugated polymer nanoparticles (NPs) have gained prominence in the bio-imaging field as an attractive class of fluorescent probes because of their interesting photoluminescence properties
PCDTBT nanoparticles of different size, ranging from 58 nm for the largest particles to 19 nm for the smallest particles, were synthesized by combining mini-emulsion-solvent evaporation method
Lowering the polymer concentration in the dispersed phase resulted in smaller particles
Summary
Over the past decade, conjugated polymer nanoparticles (NPs) have gained prominence in the bio-imaging field as an attractive class of fluorescent probes because of their interesting photoluminescence properties They have a high absorption cross-section, high radiative rates, excellent photostability, non-blinking behavior and less susceptible to leaching as compared to small molecular weight organic dyes [1,2]. NPs, i.e., MDMO-PPV (poly[2-methoxy-5-(30 ,70 -dimethyloctyloxy)-1,4-phenylene vinylene]) and CPM-MDMO-PPV (2-(5’-methoxycarbonylpentyloxy)-5-methoxy-1,4-phenylene vinylene), were tested in our group [11]. As the latter introduce carboxyl groups at the NP surface, the coupling of biomolecules to the nanoparticles was successfully demonstrated [12]
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