title: Squaraine-based polymer dots with narrow, bright near-infrared fluorescence for biological applications.
abstract: 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.
authors.affiliation: Department of Chemistry, University of Washington , Seattle, Washington 98195, United States.
authors.forename: I-Che
authors.initials: IC
authors.lastname: Wu
authors.forename: Jiangbo
authors.initials: J
authors.lastname: Yu
authors.forename: Fangmao
authors.initials: F
authors.lastname: Ye
authors.forename: Yu
authors.initials: Y
authors.lastname: Rong
authors.forename: Maria Elena
authors.initials: ME
authors.lastname: Gallina
authors.forename: Bryant S
authors.initials: BS
authors.lastname: Fujimoto
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhang
authors.forename: Yang-Hsiang
authors.initials: YH
authors.lastname: Chan
authors.forename: Wei
authors.initials: W
authors.lastname: Sun
authors.forename: Xing-Hua
authors.initials: XH
authors.lastname: Zhou
authors.forename: Changfeng
authors.initials: C
authors.lastname: Wu
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Chiu
mesh_terms: D003503:Cyclobutanes / Q000138:chemical synthesis / Q000737:chemistry*; D005434:Flow Cytometry; D005453:Fluorescence; D006801:Humans; D007259:Infrared Rays; D061986:MCF-7 Cells; D015394:Molecular Structure; D009369:Neoplasms / Q000473:pathology*; D010316:Particle Size; D010636:Phenols / Q000138:chemical synthesis / Q000737:chemistry*; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry*; D045663:Quantum Dots; D012666:Semiconductors; D013499:Surface Properties
chemical_list: D003503:Cyclobutanes; D010636:Phenols; D011108:Polymers; C480596:squaraine