Near-infrared light mediated bioimaging and photodynamic therapy based on upconversion nanoparticles coupled persistent luminescence particles

Abstract

Lanthanide (Ln3+)-based upconversion nanoparticles (UCNPs) and persistent luminescent particles (PLPs) have unique optical properties that make them attractive for a wide variety of biomedicine applications. On the one hand, UCNPs stand out for their ability to convert low energy NIR photons into higher energy UV-visible photons that allows them to have great advantages over other types of luminescent compounds and materials. In addition to the excitation of UCNPs in the NIR region, they offer other interesting optical properties including sharp and strong luminescence signals, long luminescence lifetime, multiple and tunable emissions in a wide range of the electromagnetic spectrum (UV-Vis-NIR), low autofluorescence background signal and minimal attenuation by biological tissues. Meanwhile, PLPs are able to work as an optical battery, storing energy after excitation, generally in the UV-Vis region and then slowly emitting lower energy photons for a long time after the excitation light is off. Among their most interesting properties are the intense and long duration of the emission after just a few minutes of exposure to the excitation light, the possibility of their photoexcitation over a wide range of the electromagnetic spectrum (X-rays/UV/Vis) without affecting tissues (since the excitation can be performed before the injection into the patient), complete separation of the excitation and emission processes, allowing minimal tissue absorption and low autofluorescence making them suitable for biomedical fluorescence imaging. The combination of the fantastic characteristics of these two types of particles (UCNPs and PLPs) presents great potential for diagnostic and therapeutic applications (such as bioimaging and photodynamic therapy (PDT)) in which optimal signal-to-noise ratio, high spatial emission resolution, deep tissue penetration of excitation light and low autofluorescence background signal are necessary. The main objective of this proposal is the development of UCNPs/PLPs systems and evaluate their application in bioimaging and PDT for cancer, where initially the composite material can be externally excited by UV-Vis light, injected into the tissue for obtaining optical imaging or treatment by PDT and re-activated under NIR excitation of the UCNPs, which after emitting in the UV-Vis can excite the PLPs, achieving optical bioimaging or treatment by PDT during several excitation cycles. (AU)