Probable ideal size of Ln3+-based upconversion nanoparticles for single and multimodal imaging

In this article we will discuss single and multimodal imaging with Ln3+-based nanoparticles (NPs). The single modal imaging will comprise imaging with up-conversion (UC) and magnetic resonance (MR) imaging. UC is a non-linear process in which two or more low-energy photons are converted into one higher energy photon. UCNPs are promising bioimaging probes with attractive features, such as no auto-fluorescence but still suffer from improved penetration depth as compared to 2- and 3-photon microscopy. Furthermore, we have discussed the principle of MR relaxation and highlight the current update of Ln3+-based (Ln = Dy3+, Ho3+, and Gd3+) NPs as a potential MR imaging contrast agent. Finally, we have discussed the multimodal imaging with the Ln3+-based NPs which is a novel approach that incorporates two or more complementary imaging modalities in single examination of diagnostic.