Star-shaped glycosylated conjugated oligomer for two-photon fluorescence imaging of live cells

A star-shaped glycosylated conjugated oligomer, 4,4′,4″-tris(4- (2-(4-(benzo[d]thiazol-2-yl)phenyl)-9,9′-bis(6-thiol-β-d-glucose) -hexyl)-fluoren-7-yl)phenylamine (TFBS), is synthesized for two-photon fluorescence imaging of live cells. The high density of hydrophilic sugar side groups induces self-assembly of TFBS into nanoparticles in water with an average diameter of 61 nm. Because of the self-assembled nanostructure, TFBS has a higher quantum yield in water (Φ = 0.10), compared to its cationic counterpart, 4,4′,4″-tris(4-(2-(4-(benzo[d]thiazol-2-yl)phenyl)-9, 9′-bis(6-N,N,N-trimethylammonium)-hexyl)-fluoren-7-yl)phenylamine (TFBC) (Φ = 0.03). In addition, TFBS has a large TPA cross section (δ_max) of ∼1200 GM at 740 nm in aqueous media, which is significantly higher than that for TFBC. TFBS can be effectively internalized by the human cervical cancer cell line and accumulates in the cytoplasm, allowing for live cell two-photon fluorescence imaging upon 800-nm excitation. TFBS has also shown low cytotoxicity, which is essential for in vitro and in vivo cellular imaging and other clinical applications. This study demonstrates the significant advantages of glycosylation in molecular engineering of water-soluble fluorescent molecules for two-photon fluorescence imaging applications.