Lanthanide doped nanoparticles (Ln:NPs) hold promise as novel luminescent probes for numerous applications in nanobiophotonics. Despite excellent photostability, narrowband photoluminescence, ...efficient anti-Stokes emission and long luminescence lifetimes, which are needed to meet the requirements of multiplexed and background free detection at prolonged observation times, concern about their toxicity is still an issue for both in vivo and in vitro applications. Similar to other chemicals or pharmaceuticals, the very same properties that are desirable and potentially useful from a biomedical perspective can also give rise to unexpected and hazardous toxicities. In engineered bionanomaterials, the potentially harmful effects may originate not only from their chemical composition but also from their small size. The latter property enables the nanoparticles to bypass the biological barriers, thus allowing deep tissue penetration and the accumulation of the nanoparticles in a number of organs. In addition, nanoparticles are known to possess high surface chemical reactivity as well as a large surface-to-volume ratio, which may seriously affect their biocompatibility. Herein we survey the underlying mechanisms of nanotoxicity and provide an overview on the nanotoxicity of lanthanides and of upconverting nanoparticles.
The synthesis using the thermal decomposition of metal trifluoroacetates is being widely used to prepare oleate-capped lanthanide-doped upconverting NaYF4:Er3+/Yb3+ nanoparticles (Ln-UCNPs). These ...nanoparticles have no inherent aqueous dispersibility and inconvenient postsynthesis treatments are required to render them water dispersible. Here, we have developed a novel and facile approach to obtain water-dispersible, ligand-free, brightly upconverting Ln-UCNPs. We show that the upconversion luminescence is affected by the local environment of the lanthanide ions at the surface of the Ln-UCNPs. We observe a dramatic difference of the integrated upconverted red:green emission ratio for Ln-UCNPs dispersed in toluene compared to Ln-UCNPs dispersed in water. We can enhance or deactivate the upconversion luminescence by pH and H/D isotope vibronic control over the competitive radiative and nonradiative relaxation pathways for the red and green excited states. Direct biofunctionalization of the ligand-free, water-dispersible Ln-UCNPs will enable myriad new opportunities in targeting and drug delivery applications.
Nanoparticles of NaGdF4 doped with trivalent erbium (Er3+) and ytterbium (Yb3+) are prepared by a modified thermal decomposition synthesis from trifluoroacetate precursors in 1‐octadecene and oleic ...acid. The nanoparticles emit visible upconverted luminescence on excitation with near‐infrared light. To minimize quenching of this luminescence by surface defects and surface‐associated ligands, the nanoparticles are coated with a shell of NaGdF4. The intensity of the upconversion luminescence is compared for nanoparticles that were coated with an undoped shell (inert shell) and similar particles coated with a Yb3+‐doped shell (active shell). Luminescence is also measured for nanoparticles lacking the shell (core only), and doped with Yb3+ at levels corresponding to the doped and undoped core/shell materials respectively. Upconversion luminescence was more intense for the core/shell materials than for the uncoated nanoparticles, and is greatest for the materials having the “active” doped shell. Increasing the Yb3+ concentration in the “core‐only” nanoparticles decreases the upconversion luminescence intensity. The processes responsible for the upconversion are presented and the potential advantages of “active‐core”/“active‐shell” nanoparticles are discussed.
Nanoparticles capable of upconverting near‐infrared (NIR) light to higher energies such as visible have demonstrated extraordinary potential in biological applications on the virtue that background fluorescence is near‐zero due to the NIR excitation. However, the efficiency of the upconversion process in lanthanide‐doped nanoparticles is still quite low. Here, a core/shell architecture is illustrated (see figure) in which the active shell readily absorbs NIR light and transfers it to the active luminescent core, thereby increasing the upconversion emission.
Planar quasi-Yagi antennas including a printed balun are designed and experimentally characterised. The parasitic array driver is a folded dipole connected to a parallel stripline. The unbalanced to ...balanced transition between the input microstrip and the folded dipole terminals is obtained by linearly tapering both the microstrip and the ground plane widths. These printed antennas are more compact and directive than their counterparts based on resonant half-wavelength dipole drivers: indeed, in the presence of one director, the size of the board is about 0.4 λ0 × 0.5 λ0 and the measured gain is 7 dB.
Tetragonal barium yttrium fluoride (BaYF5) nanocrystals doped with 0.5 mol % Tm3+ and 15 mol % Yb3+ (BaYF5:Tm3+, Yb3+) were synthesized using the thermal decomposition method yielding ...rectangular-shaped nanocrystals (15 nm × 5 nm) that can (up)convert near-infrared light to higher energies such as blue, via a process known as upconversion. The upconversion spectrum of the BaYF5:Tm3+, Yb3+ nanocrystals, following excitation with 980 nm, revealed that the upconverted blue emission from the 1G4 → 3H6 transition was more intense than the infrared 3H4 → 3H6 emission at high excitation densities (90 W/cm2) contrary to what is normally observed for Tm3+/Yb3+ codoped nanomaterials. On the other hand, the infrared emission dominates at lower excitation densities (15 W/cm2) demonstrating a lack of excited Yb3+ ions to carry on the upconversion beyond the 3H4 excited state to the 1G4 excited state. A saturation of the upconversion process was observed in the power dependence studies at excitation densities above 57 W/cm2, causing a deviation in the expected number of photons required for the upconversion process. The upconversion properties of BaYF5:Tm3+, Yb3+ nanocrystals are elucidated and discussed.
The synthesis, characterization, and spectroscopy of upconverting lanthanide-doped NaYF4 nanocrystals (NCs) is presented. The monodisperse cubic NaYF4 NCs were synthesized via a thermal decomposition ...reaction of trifluoroacetate precusors in a mixture of technical grade chemicals, octadecene and the coordinating ligand oleic acid. In this straightforward method, the dissolved precursors are added slowly to the reaction solution through a stainless-steel canula resulting in highly luminescent nanocrystals with an almost monodisperse particle size distribution. The NCs were characterized through the use of transmission electron microscopy, selected area electron diffraction, 1H NMR, powder X-ray diffraction, and high-resolution luminescence spectroscopy. The NaYF4 NCs are capable of being of dispersed in nonpolar organic solvents thus forming colloidally stable solutions. The colloids of the Er3+, Yb3+ and Tm3+, Yb3+ doped NCs exhibit green/red and blue upconversion luminescence, respectively, under 980 nm laser diode excitation with low power densities.
The rapid ascent of nanoscience has garnered significant attention in recent years. Much of the interest generated has dealt with the integration of nanoparticles in various applications ranging from ...automotive and textiles to bioimaging and nanomedicine. In order for the realization of this potential, their synthesis and chemistry need to be thoroughly understood. One particularly interesting class of nanoparticles comprises a lanthanide‐doped inorganic matrix. Due to their physicochemical and optical properties, these lanthanide‐doped nanoparticles are undergoing widespread investigation in many fields, particularly for in vitro and in vivo imaging, as well as theranostics. They offer significant advantages in biological applications, particularly the extension of the system applicability to deep tissue regions of the body, a reduced scattering of the excitation wavelength, reduction of autofluorescence, and decrease in thermal loading and photodamage to the system under study. Specifically, lanthanide‐doped fluoride hosts are being propelled to the forefront of the current research efforts as they offer several advantages relative to other studied upconverting host materials. This review will take an in‐depth look at lanthanide‐doped upconverting fluoride nanoparticles with a particular emphasis on the synthesis, nucleation, and growth mechanisms and, finally, the potential to tailor particle properties.
Lanthanide‐doped fluoride nanoparticles are regarded as efficient upconverting materials. A summary of the progress achieved to date in their synthesis is presented, with a particular emphasis on the nucleation and growth processes. A fundamental understanding of the synthesis can result in the ability to tailor nanoparticles and drive the application development of lanthanide‐based nanoparticle materials.
Immunomagnetic separation (IMS) techniques employing superparamagnetic particles can successfully isolate various components from mixtures. However, their utility can be limited for large-volume ...samples, viscous samples, or those containing a high density of particulate matter because of the need to generate high field gradients for particle recovery. Therefore, a new class of immunomagnetic particles was devised utilizing a single, macroscopic Pyrex spinbar conjugated with biorecognition elements to address these limitations. Advantages include an inherent capacity for effective mixing, an almost instantaneous recovery of the spinbar that can be performed without expensive equipment and with no loss of magnetic particles during processing, and reduced transfer of sample matrix. As a result, spinbars can provide an effective means for IMS with large-volume assays composed of complex matrices.
Lanthanide‐doped metal–organic frameworks (Ln‐MOFs) have versatile luminescence properties, however it is challenging to achieve lanthanide‐based upconversion luminescence in these materials. Here, ...1,3,5‐benzenetricarboxylic acid (BTC) and trivalent Yb3+ ions were used to generate crystalline Yb‐BTC MOF 1D‐microrods with upconversion luminescence under near infrared excitation via cooperative luminescence. Subsequently, the Yb‐BTC MOFs were doped with a variety of different lanthanides to evaluate the potential for Yb3+‐based upconversion and energy transfer. Yb‐BTC MOFs doped with Er3+, Ho3+, Tb3+, and Eu3+ ions exhibit both the cooperative luminescence from Yb3+ and the characteristic emission bands of these ions under 980 nm irradiation. In contrast, only the 497 nm upconversion emission band from Yb3+ is observed in the MOFs doped with Tm3+, Pr3+, Sm3+, and Dy3+. The effects of different dopants on the efficiency of cooperative luminescence were established and will provide guidance for the exploitation of Ln‐MOFs exhibiting upconversion.
1,3,5‐Benzenetricarboxylic acid (BTC) and Yb3+ ions were assembled into Yb‐BTC metal–organic frameworks (Yb‐BTC MOFs) showing upconversion luminescence under near‐infrared excitation via cooperative luminescence. In addition, various activators were doped into the Yb‐BTC MOFs and their upconversion luminescence and energy‐transfer mechanisms were studied. These MOFs show excellent potential for optical information storage.
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