Two-Photon Supramolecular Nanoplatform for Ratiometric Bioimaging.

Two-photon fluorescent imaging that utilizes two near-infrared photons as an excitation source affords higher penetration depth of tissue for biomedical research, compared with one-photon fluorescent imaging. However, the high laser power levels of the excitation source may induce photobleaching of two-photon dyes and photodamage to biosamples, which hampers its wide application for in vivo imaging. Inspired by supramolecular chemistry, we have developed a two-photon excited nanoprobe (TPFN) via host-guest interaction with excellent sensitivity, selectivity, biocompatibility, water solubility, and imaging penetration depth. Notably, this supramolecular assembly can significantly amplify the fluorescence intensities of guest molecules (21-fold increase), thereby affording a detection limit of 0.127 μM for sensing H2O2, which is greatly lower than that of free guest molecules (11.98 μM). In particular, ratiometric fluorescent imaging provides more accurate analysis of intracellular H2O2 via the built-in correction of the internal reference. Importantly, TPFN excited by a two-photon laser provides higher penetration depth for visualizing H2O2 in deeper liver tissues, compared with that of one-photon excitation. Thus, TPFN can serve as a powerful nanoplatform for ratiometric imaging of various species via this facile supramolecular self-assembly strategy.