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. Biological imaging: A star-shaped two-photon absorbing material (see scheme) with folic acid functionalization has been synthesized for targeted two-photon fluorescence imaging of MCF-7 cancer cells.