Hybrid semiconducting polymer dot-quantum dot with narrow-band emission, near-infrared fluorescence, and high brightness

Abstract

This communication describes a new class of semiconducting polymer nanoparticle-quantum dot hybrid with high brightness, narrow emission, near-IR fluorescence, and excellent cellular targeting capability. Using this approach, we circumvented the current difficulty with obtaining narrow-band-emitting and near-IR-fluorescing semiconducting polymer nanoparticles while combining the advantages of both semiconducting polymer nanoparticles and quantum dots. We further demonstrated the use of this new class of hybrid nanomaterial for effective and specific cellular and subcellular labeling without any noticeable nonspecific binding. This hybrid nanomaterial is anticipated to find use in a variety of in vitro and in vivo biological applications.

Figure 1

(A) Schematic showing the preparation of Pdot-Qdot hydrid nanoparticles (NPs). PFBT with amino terminal groups was converted to thiols first in order to covalently bind PFBT to the surfaces of Qdots, after which the Pdot-Qdot solution was mixed with PS-PEG-COOH in THF and then co-condensed in water via nanoprecipitation under vigorous sonication to form Qdot-embedded Pdots. (B) TEM (transmission electron microscopy) images of Pdot-Qdot NPs. The inset in the upper-left corner shows the enlarged view of a single Pdot-Qdot NP. The blue and white scale bars represent 20 nm and 2 nm, respectively. (C) DLS (dynamic light scattering) measurements showing the hydrodynamic diameters (histogram; average diameter was ~25 nm) of Pdot-Qdot NPs. QD represents Qdot.

Figure 2

Characterization of Pdot-Qdot nanoparticles (NPs). (A) UV-visible spectrum of Pdot-Qdot NPs in water. (B) Emission spectra of QD655 (dashed red line), QD705 (dashed purple line), and QD800 (dashed pink line) in decane. Emission spectra of their corresponding Pdot-Qdot forms after nanoprecipitation were shown in solid lines. (C) Single-particle fluorescence images of PFBT-DBT Pdots (PFBT blended with 4,7-di-2-thienyl-2,1,3-benzothiadiazole) (upper graph) and the corresponding histograms showing the intensity distributions (bottom graph). (D) Single-particle fluorescence images of PFBT-QD655 Pdots (upper graph) and the corresponding histograms showing the intensity distributions (bottom graph). The scale bars are 4 µm. Each histogram is based on the measurements of at least 700 individual particles.

Figure 3

Two-color confocal microscopy images of microtubules in HeLa cells labeled with Pdot-QD705-streptavidin. The blue fluorescence was from nuclear counterstain Hoechst 34580 and the red fluorescence was from Pdot-QD705-streptavidin. (A) Image of nucleus. (B) Image of microtubules. (C) The overlay of panels (A) and (B). (D–F) Images of negative control samples where cells were incubated with Pdot-QD705-streptavidin but in the absence of biotinylated primary antibody. The scale bars are 20 µm. (G–H) Flow cytometry detection of Pdot-Qdot labeled MCF-7 cells. The purple and pink lines show the fluorescence intensity distributions of Pdot-QD705-streptavidin and Pdot-QD800-streptavidin labeled cells, respectively. The black lines represent the results of negative control samples where no primary Biotin anti-human CD326 EpCAM antibody was present.