Strong two-photon-fluorescence from semiconducting polymer nanoparticles for high contrast imaging of cancerous cells

Strong two-photon-induced fluorescence was observed from a series of novel fluorescent semiconducting polymer nanoparticles using femtosecond laser pulses at 800 nm. The conjugated polymer nanoparticles were fabricated by a simple technique known as the ``mini emulsion'' technique. The quadratic dependence of the two-photon-fluorescence was confirmed by varying the laser intensity. The two-photon-absorption cross- sections of the nanoparticles were determined in aqueous dispersions by comparing with that of Rhodamine 6G. The deep penetration of the near-infrared laser together with large absorption cross-section demonstrated here, renders these fluorescent polymer nanoparticles as ideal candidates for high contrast in vivo fluorescent imaging of certain tumor cells.