Imaging nanoprobes are a group of nanosized agents developed for providing improved contrast for bioimaging. Among various imaging probes, optical sensors capable of following biological events or progresses at the cellular and molecular levels are actually actively developed for early detection, accurate diagnosis, and monitoring of the treatment of diseases. The optical activities of nanoprobes can be tuned on demand by chemists by engineering their composition, size and surface nature. This review will focus on researches devoted to the conception of nanoprobes with particular optical properties, called persistent luminescence, and their use as new powerful bioimaging agents in preclinical assays.

Ca₂Si₅N₈:Eu²⁺,Tm³⁺ presents outstanding long lasting luminescence at about 610 nm. However, to be useful for in vivo optical imaging, persistent luminescence materials should possess high optical performance combined with sizes in the nanoscale. With this aim, we investigated two different techniques for the preparation of nanoparticles from Ca₂Si₅N₈:Eu²⁺,Tm³⁺ bulk powder. First, nanoparticles were successfully prepared with the pulsed laser ablation method in liquid (abbreviated as PLAL). Secondly, nanoparticles obtained by selective sedimentation from the bulk compound resulted in satisfactory yield and allowed to perform the first real-time in vivo imaging with Ca₂Si₅N₈:Eu²⁺,Tm³⁺ host. Finally the influence of surface functionalization on the biodistribution of the probe after systemic injection is discussed.

Based upon the ambitious idea that one single particle could serve multiple purposes at the same time, the combination and simultaneous use of imaging and therapeutics has lately arisen as one of the most promising prospects among nanotechnologies directed toward biomedical applications. Intended for both therapeutics and diagnostics in vivo, highly complex nanostructures were specifically designed to simultaneously act as optical imaging probes and delivery vehicles. Yet, such multifunctional photonic nanoplatforms usually exploit fluorescence phenomena which require constant excitation light through biological tissues and thus significantly reduce the detection sensitivity due to the autofluorescence from living animals. In order to overcome this critical issue, the present article introduces a novel multifunctional agent based on persistent luminescence mesoporous nanoparticles. Being composed of a hybrid chromium-doped zinc gallate core/mesoporous silica shell architecture, we show that this nanotechnology can be used as an efficient doxorubicin-delivery vehicle presenting a higher cytotoxicity toward U87MG cells than its unloaded counterpart in vitro. In addition, we demonstrate that a persistent luminescence signal from these doxorubicin-loaded mesoporous nanophosphors opens a new way to highly sensitive detection in vivo, giving access to the real-time biodistribution of the carrier without any autofluorescence from the animal tissues. This new persistent luminescence-based hybrid nanotechnology can be easily applied to the delivery of any therapeutic agent, thus constituting a versatile and sensitive optical nanotool dedicated to both therapeutic and diagnostic applications in vivo.