Recent Advances in Design and Fabrication of Upconversion Nanoparticles and Their Safe Theranostic Applications

Abstract

Lanthanide (Ln) doped upconversion nanoparticles (UCNPs) have attracted enormous attention in the recent years due to their unique upconversion luminescent properties that enable the conversion of low-energy photons (near infrared photons) into high-energy photons (visible to ultraviolet photons) via the multiphoton processes. This feature makes them ideal for bioimaging applications with attractive advantages such as no autofluorescence from biotissues and a large penetration depth. In addition, by incorporating advanced features, such as specific targeting, multimodality imaging and therapeutic delivery, the application of UCNPs has been dramatically expanded. In this review, we first summarize the recent developments in the fabrication strategies of UCNPs with the desired size, enhanced and tunable upconversion luminescence, as well as the combined multifunctionality. We then discuss the chemical methods applied for UCNPs surface functionalization to make these UCNPs biocompatible and water-soluble, and further highlight some representative examples of using UCNPs for in vivo bioimaging, NIR-triggered drug/gene delivery applications and photodynamic therapy. In the perspectives, we discuss the need of systematically nanotoxicology data for rational designs of UCNPs materials, their surface chemistry in safer biomedical applications. The UCNPs can actually provide an ideal multifunctionalized platform for solutions to many key issues in the front of medical sciences such as theranostics, individualized therapeutics, multimodality medicine, etc.

Ultra-small fluorescent inorganic nanoparticles for bioimaging

“…Compared with previously mentioned fluorescent nanomaterials, up-conversion nanostructures, especially lanthanide-doped nanocrystals, have distinct advantages in fluorescence bioimaging, such as low autofluorescence background, large anti- 20 Stokes shifts, sharp emission bandwidth, high resistance to photobleaching, and high penetration depth and temporal resolution, [165][166][167][168][169][170][171] In addition, they can be used for multimodal bioimaging and therapy ( Figure 17). More bioapplications of upconversion nanoparticles can be found in recent reviews.…”

Hydrothermal synthesis of optically active fluoride particles doped with rare earth ions in the presence of ethylenediaminetetra acetic acid (EDTA)

“…Odlikuju se izvanrednom fotostabilnošću i niskom citotoksičnošću gde se pored izrade bioloških markera koriste i kao izvori svetlosti (fluorescentne lampe), u proizvodnji displeja (katodne cevi, plazma ekrani) i u zaštiti novčanica i dokumenata [1,2]. Fluoridi na bazi elemenata retkih zemalja tipa YF3 i NaYF4 predstavljaju idealnu matricu za ugradnju optički aktivnih jona retkih zemalja, jer poseduju visok stepen indeksa refrakcije, dobru hemijsku stabilnost i malu energiju fonona ~350-400 cm -1 [3,4].…”

Template-free synthesis and luminescent properties of hollow Ln:YOF (Ln = Eu or Er + Yb) microspheres

“…These UC phosphors, which show visible emission after excitation with infrared (IR) radiation, are of particular interest for bioapplications when compared with DC phosphors since, contrary to UV radiation, IR light does not cause photodamage to living organisms and penetrates deeply in tissues [17]. The hollow architecture confers to these materials low effective densities and a high encapsulation ability, which are very important for some of the above applications.…”

“…The former have the advantages of their high chemical and thermal stability, whereas fluorides are more preferred than oxides from the optical point of view, since the former have lower vibrational energies and consequently, the quenching of the exited state of the Ln cations through multiphonon relaxation is minimised, resulting in a higher quantum efficiency of luminescence [17,19]. Less attention has been paid to Ln oxyfluorides (LnOF), which have been suggested as excellent hosts since they combine the main advantages of oxides with those of fluorides [20].…”

“…Thus, Ln-based luminescent compounds, usually consisting of a host matrix doped with Ln cations, find important applications in lighting [13], display devices [14], solid state lasers [15] and biotechnology (labelling, imaging, drug delivery) [16,17], to mention a few. The main advantages of this kind of luminescent materials over other well known phosphors (quantum dots, organic dyes) are their high chemical and thermal resistance, photostability, low toxicity and their versatility, since they may be designed as down-conversion (DC) phosphors (when doped with Eu, Tb, Sm, Dy), which usually are excited by ultraviolet (UV) light, or as up-conversion (UC) phosphors (when co-doping with Yb and mainly Er or Tm) [16].…”