Synthesis and Characterization of Water-Soluble Conjugated Oligoelectrolytes for Near-Infrared Fluorescence Biological Imaging

• Published in: ACS applied materials & interfaces 2016-06, Vol.8 (25), p.15937-15947
• Main Authors: Woo, Shin-Jae, Park, Sungmin, Jeong, Ji-Eun, Hong, Yoochan, Ku, Minhee, Kim, Bo Yun, Jang, Il Ho, Heo, Soon Chul, Wang, Taejun, Kim, Ki Hean, Yang, Jaemoon, Kim, Jae Ho, Woo, Han Young
• Format: Article
• Language: English
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.6b04276

Near-infrared (NIR) fluorophores attract increasing attention as a molecular marker (or probe) for in vivo and in vitro biological fluorescence imaging. Three types of new NIR fluorescent conjugated oligoelectrolytes (COEs: Q-FlTBTTFl, Q-FlBBTFl, and Q-FlTBBTTFl) are synthesized with quaternized ammonium ionic groups in their side-chains for water solubility. The emission wavelength is modulated in the range 600–1300 nm, by adjusting the intramolecular charge transfer in the molecular backbone based on the electron-rich fluorene (and/or thiophene) and electron-deficient benzo­[2,1,3]­thiadiazole (or benzo­[1,2-c:4,5-c′]­bis­[1,2,5]­thiadiazole) moieties. The COEs show a remarkably larger Stokes shift (147–276 nm) compared to commercial rhodamine and cyanine dyes in water, avoiding self-quenching and interference from the excitation backscattered light. The photoluminescence (PL) quantum efficiency is improved substantially by up to 27.8% in water by fabricating a vesicular complex, COE/v, with a block ionomer, poly­[(ethylene oxide)-block-(sodium 2-acrylamido-2-methyl-1-propanesulfonate)]. In vitro cellular uptake images with the COEs are obtained with good biocompatibility by confocal single-photon and two-photon microscopy. The ex vivo and in vivo images of a mouse xenograft model treated with the Q-FlBBTFl/v exhibit a substantially stronger fluorescence signal at the tumor site than at the other organs, highlighting the potential of the COE/v as an NIR fluorescent imaging agent for the diagnosis of cancer.