Two-photon fluorescent probes for biomembrane imaging: effect of chain length.

Two-photon fluorescent probes for the cellular membrane, derived from 6-acyl-2-aminonaphthalene as the fluorophore and hexanoyl (CH), lauryl (CL), and stearyl (CS) groups as the receptor, have been synthesized. Their photophysical properties and utility as membrane probes were also studied. Whereas CH cannot be used as a membrane probe due to its high water solubility, CL and CS are useful two-photon probes for membrane lateral heterogeneity, as they can easily stain cells, emit fluorescence with high sensitivity to the environment polarity, and are capable of imaging the membrane lateral heterogeneity in live cells. Moreover, CS is more likely to be located in the plasma membrane due to its negligible water solubility. Our results show that the liquid ordered-like domain covers 31-35% of the cellular surface.