Glycosylated Star-Shaped Conjugated Oligomers for Targeted Two-Photon Fluorescence Imaging

A glucopyranose functionalized star-shaped oligomer, N-tris{4,4′,4′′-[(1E)-2-(2-{(E)-2-[4-(benzo[d]thiazol-2-yl)phenyl]vinyl}-9,9-bis(6-2-amido-2-deoxy-1-thio-β-D-glucopyranose-hexyl)-9H-fluoren-7-yl)vinyl]phenyl}phenylamine (TVFVBN-S-NH2), is synthesized for two-photon fluorescence imaging. In water, TVFVBN-S-NH2 self-assembles into nanoparticles with an average diameter of ∼49 nm and shows a fluorescence quantum yield of 0.21. Two-photon fluorescence measurements reveal that TVFVBN-S-NH2 has a two-photon absorption cross-section of ∼1100 GM at 780 nm in water. The active amine group on the glucopyranose moiety allows further functionalization of TVFVBN-S-NH2 with folic acid to yield TVFVBN-S-NH2FA with similar optical and physical properties as those for TVFVBN-S-NH2. Cellular imaging studies reveal that TVFVBN-S-NH2FA has increased uptake by MCF-7 cells relative to that for TVFVBN-S-NH2, due to specific interactions between folic acid and folate receptors on the MCF-7 cell membrane. This study demonstrates the effectiveness of glycosylation as a molecular engineering strategy to yield water-soluble materials with a large two-photon absorption (TPA) cross-section for targeted cancer-cell imaging.