Deep, High Contrast Microscopic Cell Imaging Using Three-Photon Luminescence Of Beta-(Nayf4:Er3+/Nayf4) Nanoprobe Excited By 1480-Nm Cw Laser Of Only 1.5-Mw

It is challenging to achieve deep microscopic imaging for the strong scattering in biotissue. An efficient three-photon luminescence can effectively increase the penetration depth. Here we report that beta-NaYF4: Er3+/NaYF4 UCNPs were excited by a 1480-nm CW-laser and emitted 543/653-nm light through a three-photon process. With the merit of the hexagonal crystal phase, sub-milliwatt laser power was utilized to excite the UCNP-probed cells to minimize the heating effect. The polymer-coated UCNPs were shown to be harmless to cells. The deep, high contrast in vitro microscopic imaging was implemented through an artificial phantom. Imaging depth of 800 mu m was achieved using only 1.5 mW excitation and a 0.7 NA objective. The green/red emission intensities ratio after penetrating the phantom was studied, indicating that longer emission wavelength is preferred for deep multiphoton microscopy. The proposed and demonstrated beta-UCNPs would have great potential in three-photon microscopy. (C) 2015 Optical Society of America