Upconverting nanophosphors for bioimaging.

Upconverting nanoparticles (UCNPs) when excited in the near-infrared (NIR) region display anti-Stokes emission whereby the emitted photon is higher in energy than the excitation energy. The material system achieves that by converting two or more infrared photons into visible photons. The use of the infrared confers benefits to bioimaging because of its deeper penetrating power in biological tissues and the lack of autofluorescence. We demonstrate here sub-10 nm, upconverting rare earth oxide UCNPs synthesized by a combustion method that can be stably suspended in water when amine modified. The amine modified UCNPs show specific surface immobilization onto patterned gold surfaces. Finally, the low toxicity of the UCNPs is verified by testing on the multi-cellular C. elegans nematode.