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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]

In this study, we describe a solutionprocedure for the preparationand surface modification of photostable colloidal silicon quantumdots (SiQDs) for imaging of cancer cells. Photoluminescent SiQDs weresynthesized by reduction of halogenated silane precursors using amicroemulsion process. It was shown that 1,8-nonadiyne molecules couldbe grafted onto the surface of hydrogen-terminated SiQDs via ultraviolet(UV)-promoted hydrosilylation, demonstrated by Fourier transform infraredspectroscopy (FTIR) measurements. In addition, various azide moleculeswere coupled onto nonadiyne-functionalized particles, rendering particlesdispersible in selected polar and nonpolar solvents. The photoluminescenceof functionalized SiQDs was stable against photobleaching and didnot vary appreciably within biologically applicable pH and temperatureranges. To demonstrate compatibility with biological systems, water-solubleSiQDs were used for fluorescent imaging of HeLa cells. In addition,the SiQDs were shown to be non-cytotoxic at concentrations up to 240μg/mL. The results presented herein provide good evidence forthe versatility of functionalized SiQDs for fluorescent bioimagingapplication. [ABSTRACT FROM AUTHOR]