Conjugated-Polymer-Based Red-Emitting Nanoparticlesfor Two-Photon Excitation Cell Imaging with High Contrast.

Two-photonfluorescence microscopy is a widely used noninvasivebioimaging technique because of unique advantages such as a largepenetration depth and 3D mapping capability. Ideal two-photon fluorophoresrequire large two-photon absorption cross sections and red emissionwith high quantum yields. Here we report red-emitting-dye-doped conjugatedpolymer nanoparticles that display high two-photon excitation brightness.In these nanoparticles, conjugated polymer (PFV) was chosen as a two-photonlight-harvesting material, and red-emitting dyes (MgPc and Nile red)were chosen as the energy acceptors and red-emitting materials. Two-photonexcitation fluorescence of MgPc and Nile red was enhanced by up to∼53 and ∼240 times, respectively. We have successfullydemonstrated the application of these conjugated polymer-based nanoparticlesin two-photon excitation cancer cell imaging with an excellent contrastratio. This concept could become a general approach to the preparationof two-photon excitation red-emitting materials for deep-tissue live-cellimaging with high contrast. [ABSTRACT FROM AUTHOR]