Recent Advances of Upconversion Nanomaterials in the Biological Field

Abstract

Rare Earth Upconversion nanoparticles (UCNPs) are a type of material that emits high-energy photons by absorbing two or more low-energy photons caused by the anti-stokes process. It can emit ultraviolet (UV) visible light or near-infrared (NIR) luminescence upon NIR light excitation. Due to its excellent physical and chemical properties, including exceptional optical stability, narrow emission band, enormous Anti-Stokes spectral shift, high light penetration in biological tissues, long luminescent lifetime, and a high signal-to-noise ratio, it shows a prodigious application potential for bio-imaging and photodynamic therapy. This paper will briefly introduce the physical mechanism of upconversion luminescence (UCL) and focus on their research progress and achievements in bio-imaging, bio-detection, and photodynamic therapy.

Light-Triggered Polymersome-Based Anticancer Therapeutics Delivery

“…Hence, unlike the vast reported light-responsive systems involving UV or short excitation radiation, UCNPs allow the drug release at longer wavelengths. Further, the anti-stokes phenomenon under NIR irradiation leads to shifted visible and UV light emission, whereas the autofluorescence background is minimal, and the light scattering of biological tissues is significantly reduced [ 280 , 281 , 282 , 283 , 284 , 285 ]. Thus, attaching light-activable moieties onto UCNPs makes upconverting the transducer possible, then absorbs NIR light with the emission of photons with a shorter wavelength and the induction of photoreactions, leading to the triggering of therapeutic agents and/or phototherapy activation.…”

Lanthanide-Doped Upconversion Luminescent Nanoparticles—Evolving Role in Bioimaging, Biosensing, and Drug Delivery

“…Using a combination of energy migration and core–shell structural engineering to improve properties for a wide range of activators would widen the range of applications for lanthanide-doped nanoparticles [ 53 , 54 , 55 ]. Surface modification is required for specific nanomaterials to fulfil various biological activities, in biosciences such as disease therapy (particularly cancer) [ 56 , 57 ], detection [ 58 ], and immunoassay [ 59 ].…”

Synthesis of near-infrared-responsive hexagonal-phase upconversion nanoparticles with controllable shape and luminescence efficiency for theranostic applications

“…26 In addition, there are five basic upconversion mechanisms for lanthanide-doped UCNs (a) excited-state absorption (ESA), (b) energy transfer upconversion (ETU), (c) cross-relaxation (CR), (d) photon avalanche (PA), and (e) cooperative sensitization upconversion (CSU). [52][53][54] In this way, the two or more photon absorptions of 980 nm photons by Yb 3+ ions are followed by double excitation of Er 3+ , multi-phonon relaxations, and emission of visible photons ( 4 I 15/2 → 4 I 11/2 → 4 F 7/2 → ( 2 H 11/2 , 4 S 3/2 , 4 F 9/2 ) → 4 I 15/2 ) for both the green and the red emission. 55 Figure 5(C) shows the upconversion luminescence spectra of UCN-50-300-1, UCN-80-300-1, and UCN-60-300-6.…”