posted on 2015-12-17, 06:53authored byI-Che Wu, Jiangbo Yu, Fangmao Ye, Yu Rong, Maria
Elena Gallina, Bryant S. Fujimoto, Yong Zhang, Yang-Hsiang Chan, Wei Sun, Xing-Hua Zhou, Changfeng Wu, Daniel T. Chiu
This
article describes the design and development of squaraine-based
semiconducting polymer dots (Pdots) that show large Stokes shifts
and narrow-band emissions in the near-infrared (NIR) region. Fluorescent
copolymers containing fluorene and squaraine units were synthesized
and used as precursors for preparing the Pdots, where exciton diffusion
and likely through-bond energy transfer led to highly bright and narrow-band
NIR emissions. The resulting Pdots exhibit the emission full width
at half-maximum of ∼36 nm, which is ∼2 times narrower
than those of inorganic quantum dots in the same wavelength region
(∼66 nm for Qdot705). The squaraine-based Pdots show a high
fluorescence quantum yield (QY) of 0.30 and a large Stokes shift of
∼340 nm. Single-particle analysis indicates that the average
per-particle brightness of the Pdots is ∼6 times higher than
that of Qdot705. We demonstrate bioconjugation of the squaraine Pdots
and employ the Pdot bioconjugates in flow cytometry and cellular imaging
applications. Our results suggest that the narrow bandwidth, high
QY, and large Stokes shift are promising for multiplexed biological
detections.