In vivo and scanning electron microscopy imaging of up-converting nanophosphors in Caenorhabditis elegans.

We show here that upconversion phosphors can be imaged both by infrared excitation and in a scanning electron microscope. We have synthesized and characterized for this work up-converting phosphor nanoparticles nonaggregated nanocrystals of size range 50-200 nm. We have investigated the optical properties of 50-200 nm nanoparticles and found a square dependence of the emitted visible fluorescence on the infrared excitation and verified that under electron excitation similar narrow band emission spectra can be obtained as is seen with IR upconversion. The viability of the nanoparticles for biological imaging was confirmed by imaging the digestive system of the nematode worm Caenorhabditis elegans, and we have confirmed using energy-dispersive X-ray analysis that the up-conversion nanoparticles can be identified in a scanning electron microscope at high spatial resolution.