Upconversion processes: versatile biological applications and biosafety

Abstract

Lanthanide-doped photon upconverting nanomaterials are evolving as a new class of imaging contrast agents, offering highly promising prospects in the area of biomedical applications. Owing to their ability to convert long-wavelength near-infrared excitation radiation into shorter-wavelength emissions, these nanomaterials are well suited to yield properties of low imaging background, large anti-Stokes shift, along with high optical penetration depth of NIR light for deep tissue optical imaging or light-activated drug release and therapy. Such materials have potential for significant advantages in analytical applications compared to molecular fluorophores and quantum dots. The use of IR radiation as an excitation source diminishes autofluorescence and scattering of excitation radiation, which leads to a reduction of background in optical experiments. The upconverting nanocrystals show exceptional photostability and are constituted of materials that are not significantly toxic to biological organisms. Excitation at long wavelengths also minimizes damage to biological materials. In this detailed review, various mechanisms operating for the upconversion process, and methods that are utilized to synthesize and decorate upconverting nanoparticles are investigated to elucidate by what means absorption and emission can be tuned. Up-to-date reports concerning cellular internalization, biodistribution, excretion, cytotoxicity and in vivo toxic effects of UCNPs are discussed. Specifically, studies which assessed the relationship between the chemical and physical properties of UCNPs and their biodistribution, excretion, and toxic effects are reviewed in detail. Finally, we also deliberate the challenges of guaranteeing the biosafety of UCNPs in vivo.

Excretable Lanthanide Nanoparticle for Biomedical Imaging and Surgical Navigation in the Second Near‐Infrared Window

“…[12][13][14][15][16][17] Recently, tremendous efforts have been devoted to design and synthesize NIR-II fluorophores with high performance, including organic molecules [16][17][18][19] and inorganic nanoparticles. [15,[31][32][33][34][35][36] Current researches have elucidated that the major excretory routes including renal pathway (bladder and urine) and hepatobiliary process (bile to feces) of nanoparticles are determined primarily by the size and surface charge of the nanoparticles. [13] Compared with several other NIR-II inorganic fluorophores such as quantum dots (QDs) and singlewalled carbon nanotubes (SWNTs), growing interests have been focused to rare earth-doped nanoparticles (RENPs) because of their large Stokes shifts, narrow and multipeak emission profiles, negligible excitation-emission band overlap, and excellent photostability.…”

Upconversion nanoparticle bioconjugates characterized by capillary electrophoresis

“…Moreover, UCNPs are a great candidate for in‐depth imaging, since NIR excitation light penetrates deeper to the tissue, which is in agreement with optical transmission window of the tissue (650–1000 nm) . Another convenient feature that may overcome the limitations of traditional fluorophores is high resistance to photobleaching and photobrightening, as well as low toxicity, declared by numerous promising applications described in recent reviews .…”

“…Moreover, UCNPs are a great candidate for in-depth imaging, since NIR excitation light penetrates deeper to the tissue, which is in agreement with optical transmission window of the tissue (650-1000 nm) [3][4][5]. Another convenient feature that may overcome the limitations of traditional fluorophores is high resistance to photobleaching and photobrightening, Correspondence: Dr. Marketa Vaculovicova, Department of Chemistry and Biochemistry, Mendel University in Brno, Zemedelska 1, CZ-613 00 Brno, Czech Republic Fax: +420-5-4521-2044 E-mail: marketa.ryvolova@seznam.cz Abbreviations: COOH-UCNP, carboxyl-silica-coated upconversion nanoparticle; DLS, dynamic light scattering; EDS, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride; FA, folic acid; NIR, near-infrared; Sulfo-NHS, Nhydroxysulfosuccinimide; UCNP, upconversion nanoparticle as well as low toxicity, declared by numerous promising applications described in recent reviews [6][7][8][9].…”

Recent Advancements in Ln‐Ion‐Based Upconverting Nanomaterials and Their Biological Applications

“…In conventional host luminescent nanomaterials, anti‐Stokes emission is generated through simultaneous two‐photon absorption (STPA) and second harmonic generation (SHG) . These photon absorption processes need an ultrashort pulse laser (e.g., femtosecond pulse laser) with extremely high exciting power‐density (10 6 –10 9 W cm −2 ) to produce large numbers of excitation photons and, the use of such a pulse laser is very expensive . Another drawback is the use of non‐centrosymmetric molecular structure with a weak D–π–A configuration (D: donor, A: acceptor) that results in low two‐photon absorption (TPA) capacity .…”