Preparation and Two-Photon Imaging of a Water-Soluble Fluorescent Nanoparticle

A water-soluble polymeric fluorescent nanoparticle (PTCN) has been proposed for two-photon fluorescence (TPF) imaging of living cells. PTCN was firstly prepared by chemical crosslinking of polyethyleneimine using a dual carboxyl 1, 8-naphthalimide derivative as the crosslinker. Subsequently, the investigations on its structure, morphology, one- and two-photon fluorescence properties and cytotoxicity were carried out. It was found that PTCN was spherical with the diameters of 5-10 nm. It could emit fluorescence at 536 nm with the excitation wavelengths of 443 nm and 800 nm, respectively. PTCN possessed good pH stability and photostability. Its fluorescence did not change in the pH range of 4.0-9.0. In pH 7.4 buffer solution, when it was detected at lambda(ex)/lambda(em) = 443 nm/536 nm for 12000 times, the decrease in fluorescence intensity was less than 1%. Cytotoxic assays indicated it was low toxic upon interactions with Hela cells for 24 h at a concentration of 15.0 mg/L. Finally, the application of PTCN for imaging live cells was assessed by TPF microscopy technique. After Hela cells were incubated with PTCN for 2 h, the green fluorescence was observed in the cellsap at the excitation wavelength of 800 nm. The proposed nanoparticle is potential in the development of targeting TPF probes.