Fig. 1. Construction and characterization of the two-photon fluorescent covalent organic framework nanoprobe TpASH-NPHS. (A) Synthesis of TpASH and its sequential post-synthesis modification. (B) TEM and (C) SEM images of TpASH, TpASH-Glc and TpASH-NPHS. (D) FTIR spectra of TpASH after sequential post-synthesis modification. (E) AFM image of the COF nanoprobe TpASH-NPHS. Inset: the image of the Tyndall effect of the TpASH-NPHS suspension (left: TpASH-NPHS and right: water; source of laser light on the left). (F) The size distribution of the COF nanoprobe TpASH-NPHS by DLS.