Synthesis of highly fluorescent LaF3:Ln3+/LaF3 core/shell nanocrystals by a surfactant-free aqueous solution route

Sustained and Localized Drug Depot Release Using Radiation-Activated Scintillating Nanoparticles

Clinical treatment of cancer commonly incorporates X-ray radiation therapy (XRT), and developing spatially precise radiation-activatable drug delivery strategies may improve XRT efficacy while limiting off-target toxicities associated with systemically administered drugs. Nevertheless, achieving this has been challenging thus far because strategies typically rely on radical species with short lifespans, and the inherent nature of hypoxic and acidic tumor microenvironments may encourage spatially heterogeneous effects. It is hypothesized that the challenge could be bypassed by using scintillating nanoparticles that emit light upon X-ray absorption, locally forming therapeutic drug depots in tumor tissues. Thus a nanoparticle platform (Scintillating nanoparticle Drug Depot; SciDD) that enables the local release of cytotoxic payloads only after activation by XRT is developed, thereby limiting off-target toxicity. As a proof-of-principle, SciDD is used to deliver a microtubule-destabilizing payload MMAE (monomethyl auristatin E). With as little as a 2 Gy local irradiation to tumors, MMAE payloads are released effectively to kill tumor cells. XRT-mediated drug release is demonstrated in multiple mouse cancer models and showed efficacy over XRT alone (p < 0.0001). This work shows that SciDD can act as a local drug depot with spatiotemporally controlled release of cancer therapeutics.

Fabrication and characterization of core-shell microparticles containing an aqueous core

Core-shell microparticles containing an aqueous core have demonstrated their value for microencapsulation and drug delivery systems. The most important step in generating these uniquely structured microparticles is the formation of droplets and double emulsion. The droplet generator must meet the performance and reliability requirements, including accurate size control with tunability and monodispersity. Herein, we present a facile technique to generate surfactant-free core-shell droplets with an aqueous core in a microfluidic device. We demonstrate that the geometry of the core-shell droplets can be precisely adjusted by the flow rates of the droplet components. As the shell is polymerized after the formation of the core-shell droplets, the resulting solid microparticles ensure the encapsulation of the aqueous core and prevent undesired release. We then study experimentally and theoretically the behaviour of resultant microparticles under heating and compression. The microparticles demonstrate excellent stability under both thermal and mechanical loads. We show that the rupture force can be quantitatively predicted from the shell thickness relative to the outer shell radius. Experimental results and theoretical predictions confirm that the rupture force scales directly with the shell thickness.

Role of heat treatment on the structural and luminescence properties of Yb3+/Ln3+ (Ln = Tm, Ho and Er) co-doped LaF3 nanoparticles

Hexagonal LaF₃:Yb³⁺/Ln³⁺ and tetragonal LaOF:Yb³⁺/Ln³⁺ (Ln = Ho, Tm, Er) have been successfully prepared via a two-step reaction, which includes a facile aqueous ligand free solution method and the following heat treatment of the as-prepared LaF₃ precursor. The phase formation evolution from LaF₃ to LaOF with different phase structures was characterized by X-ray diffraction (XRD), scanning electron microscopy, Fourier transform infrared, and Raman spectroscopy. At an annealing temperature of 500 °C pure hexagonal LaF₃:Yb³⁺/Ln³⁺ (Ln = Ho, Tm, Er) nanoparticles with an average size of 32 nm were obtained and they showed a strong visible upconversion and a modest infrared emission upon 976 nm laser excitation. Further, using an annealing temperature of 900 °C, tetragonal LaOF:Yb³⁺/Ln³⁺ (Ln = Ho, Tm, Er) nanoparticles with a size of around 44 nm were obtained (obtained from XRD) and an expressive enhancement in the emission of the VIS and near-infrared regions was observed. These results envision applications that require efficient emissions such as fluorescent and thermal images, and LaF₃ nanocrystals have recently been widely explored for applications in biological systems.

Synthesis and Rational design of Europium and Lithium Doped Sodium Zinc Molybdate with Red Emission for Optical Imaging

Highly efficient fluorescent and biocompatible europium doped sodium zinc molybdate (NZMOE) nanoprobes were successfully synthesized via Polyol method. Non-radiative defect centres get reduced with Li+ co-doping in NZMOE nanoprobes. XRD spectra and Rietveld refinement confirmed successful incorporation of lithium ion and crystallinity was also improved with Li+ co-doping. The shape of phosphor is rod shaped, as determined by TEM. Significant enhancement in photoluminescence intensity was observed with 266, 395 and 465 nm excitations. Profound red emission was recorded for 5 at% Li+ co-doped NZMOE nanoprobes with 266 nm excitation. It shows high asymmetry ratio (~15), color purity (94.90%) and good quantum efficiency (~70%). Judd Ofelt parameters have been calculated to measure intensity parameters and radiative transition rates. In order to measure biocompatibility of the nanoprobes, cytotoxicity assays were performed with HePG2 cells. The fluorescence emitted from phosphor material treated HePG2 cells was also measured by Laser Scanning Confocal Microscopy. The bright red fluorescence in HePG2 cells treated with very low concentration (20 μg/ml) of phosphor material indicates that it could be a promising phosphor for biological detection or bio-imaging.

Efficient multicolor tunability of ultrasmall ternary-doped LaF3 nanoparticles: energy conversion and magnetic behavior

Luminescence-tunable multicolored LaF₃:xCe³⁺,xGd³⁺,yEu³⁺ (x = 5; y = 1, 5, 10, and 15 mol%) nanoparticles have been synthesized via a low cost polyol method. Powder X-ray diffraction and high-resolution transmission electron microscopy studies confirm the hexagonal phase of the LaF₃:xCe³⁺,xGd³⁺,yEu³⁺ nanophosphors with average sizes (oval shape) ranging from 5 to 7 nm. Energy-dispersive X-ray spectroscopy analyses show the uniform distribution of Ce³⁺, Gd³⁺, and Eu³⁺ dopants in the LaF₃ host matrix. The photoluminescence spectra and electron paramagnetic resonance measurements guarantee the presence of Eu²⁺, corroborated through DC susceptibility measurements of the samples displaying paramagnetic behavior at 300 K, whereas weak ferromagnetic ordering is shown at 2 K. The non-radiative energy transfer processes from the 4f(²F_5/2) → 5d state (Ce³⁺) to the intraconfigurational 4f excited levels of rare earth ions and simultaneous emissions in the visible region from the 4f⁶5d¹ (Eu²⁺) and ⁵D₀ (Eu³⁺) emitting levels, leading to overlapped broad and narrow emission bands, have been proclaimed. The energy transfer mechanism proposes involvement of the Gd³⁺ ion sub-lattice as the bridge and finally trapping by Eu^2+/3+, upon excitation of the Ce³⁺ ion. The calculation of experimental intensity parameters (Ω_2,4) has been discussed and the highest emission quantum efficiency (η = 85%) of the Eu³⁺ ion for the y = 10 mol% sample is reported. The advantageous existence of the Eu²⁺/Eu³⁺ ratio along with variously doped nanomaterials described in this work, results in tunable emission color in the blue-white-red regions, highlighting the potential application of the samples in solid-state lighting devices, scintillation devices, and multiplex detection.

Imaging agents based on lanthanide doped nanoparticles

This review summarizes the recent progress of single and multimodal imaging agents based on lanthanide doped nanoparticles.

Neodymium-doped LaF(3) nanoparticles for fluorescence bioimaging in the second biological window

The future perspective of fluorescence imaging for real in vivo application are based on novel efficient nanoparticles which is able to emit in the second biological window (1000-1400 nm). In this work, the potential application of Nd(3+) -doped LaF(3) (Nd(3+) :LaF(3) ) nanoparticles is reported for fluorescence bioimaging in both the first and second biological windows based on their three main emission channels of Nd(3+) ions: (4) F(3/2) →(4) I(9/2) , (4) F(3/2) →(4) I(11/2) and (4) F(3/2) →(4) I(13/2) that lead to emissions at around 910, 1050, and 1330 nm, respectively. By systematically comparing the relative emission intensities, penetration depths and subtissue optical dispersion of each transition we propose that optimum subtissue images based on Nd(3+) :LaF(3) nanoparticles are obtained by using the (4) F3/2 →(4) I11/2 (1050 nm) emission band (lying in the second biological window) instead of the traditionally used (4) F(3/2) →(4) I(9/2) (910 nm, in the first biological window). After determining the optimum emission channel, it is used to obtain both in vitro and in vivo images by the controlled incorporation of Nd(3+) :LaF(3) nanoparticles in cancer cells and mice. Nd(3+) :LaF(3)nanoparticles thus emerge as very promising fluorescent nanoprobes for bioimaging in the second biological window.

The impact of shell host (NaYF₄/CaF₂) and shell deposition methods on the up-conversion enhancement in Tb³⁺, Yb³⁺ codoped colloidal α-NaYF₄ core-shell nanoparticles

Lanthanide doped, up-converting nanoparticles have found considerable interest as luminescent probes in the field of bio-detection. Although the nanoparticles (NPs) have already been successfully applied for fluorescent bio-imaging and bio-assays, the efficiency of the up-conversion process seems to be the bottle-neck in rigorous applications. In this work, we have shown enhancement of the up-conversion in colloidal α-NaYF₄:Yb(3+), Tb(3+) doped nanocrystals owing to passivation of their surface. We have studied quantitatively the influence of the shell type (NaYF₄ and CaF₂), its thickness, as well as the shell deposition method (i.e. single thick shell vs. multi-layer shell) on the luminescent properties of the nanoparticles. The results showed that up to 40-fold up-conversion intensity enhancement may be obtained for the core-shell nanoparticles in comparison with the bare core nanoparticles, irrespective of the shell type and deposition method. Moreover, the suitability of the NaYF₄:Yb(3+), Tb(3+) core-shell NPs for multi-color emission and spectral multiplexing has been presented.

Subtissue thermal sensing based on neodymium-doped LaF₃ nanoparticles

In this work, we report the multifunctional character of neodymium-doped LaF₃ core/shell nanoparticles. Because of the spectral overlap of the neodymium emission bands with the transparency windows of human tissues, these nanoparticles emerge as relevant subtissue optical probes. For neodymium contents optimizing the luminescence brightness of Nd³⁺:LaF₃ nanoparticles, subtissue penetration depths of several millimeters have been demonstrated. At the same time, it has been found that the infrared emission bands of Nd³⁺:LaF₃ nanoparticles show a remarkable thermal sensitivity, so that they can be advantageously used as luminescent nanothermometers for subtissue thermal sensing. This possibility has been demonstrated in this work: Nd³⁺:LaF₃ nanoparticles have been used to provide optical control over subtissue temperature in a single-beam plasmonic-mediated heating experiment. In this experiment, gold nanorods are used as nanoheaters while thermal reading is performed by the Nd³⁺:LaF₃ nanoparticles. The possibility of a real single-beam-controlled subtissue hyperthermia process is, therefore, pointed out.

Dual-emitting nanocomposites derived from rare-earth compound nanotubes for ratiometric fluorescence sensing applications

A new class of ratiometric fluorescence sensors composed of rare-earth (RE) compound nanotubes is described. Polyethylenimine-coated yttrium hydroxide fluoride nanotubes (YHF NTs) that were synthesized hydrothermally exhibit highly efficient fluorescence when doped with RE ions. The polyethylenimine on the NTs facilitates the incorporation of phosphors such as quantum dots or organic dyes onto the NT surface to produce dual-emitting nanocomposites which are excellent ratiometric fluorescence sensors. The phosphor layer and underlying tubes in the nanocomposites act as the indicator and reference probes, respectively. This ratiometric fluorescence method which can be applied to the detection of heavy metals in solutions, temperature sensing, and pH sensing boasts high sensitivity and selectivity as well as better accuracy than traditional intensity-based fluorescence methods.

Efficient manganese luminescence induced by Ce3+-Mn2+ energy transfer in rare earth fluoride and phosphate nanocrystals

Manganese materials with attractive optical properties have been proposed for applications in such areas as photonics, light-emitting diodes, and bioimaging. In this paper, we have demonstrated multicolor Mn2+ luminescence in the visible region by controlling Ce3+-Mn2+ energy transfer in rare earth nanocrystals [NCs]. CeF3 and CePO4 NCs doped with Mn2+ have been prepared and can be well dispersed in aqueous solutions. Under ultraviolet light excitation, both the CeF3:Mn and CePO4:Mn NCs exhibit Mn2+ luminescence, yet their output colors are green and orange, respectively. By optimizing Mn2+ doping concentrations, Mn2+ luminescence quantum efficiency and Ce3+-Mn2+ energy transfer efficiency can respectively reach 14% and 60% in the CeF3:Mn NCs.

Up-conversion luminescence of the NaRF4-NaR'F4 (R: Y, Yb, Er) core-shell nanomaterials

Up-converting NaRF(4)-NaR'F(4) (R: Y, Yb, Er) nanomaterials with different core-shell combinations were prepared with the co-precipitation method. The X-ray powder diffraction (XPD) measurements revealed the presence of both the cubic and hexagonal NaRF(4) phases. The crystallite sizes calculated with the Scherrer formula were 100 and 150 nm for the cubic and hexagonal phases, respectively. The FT-IR spectra showed water impurities. The up-conversion luminescence and luminescence decays were studied with NIR laser excitation at 970 nm. The up-conversion luminescence spectra showed strong red (640-685 nm) ((4)F(9/2) → (4)I(15/2)) and moderate green (515-560 nm) ((2)H(11/2,) (4)S(3/2) → (4)I(15/2)) Er(3+) luminescence. The strongest up-conversion luminescence and longest red luminescence decay was obtained from the Na(Y,Yb)F(4)-NaErF(4) core-shell combination.

Controllable energy transfer in fluorescence upconversion of NdF3 and NaNdF4 nanocrystals

The synthesized Nd fluoride nanocrystals exhibited different upconversion behaviors as dispersed and aggregated samples due to the different energy transfer mechanisms. When they were dispersed in water, the NaNdF(4) nanocrystals exhibited approximately 400 times stronger upconversion fluorescence than the NdF(3) nanocrystals. Remarkable upconversion behaviors were found when the nanocrystals were aggregated in the films. For the NdF(3) nanocrystals, the energy transfer processes (4)I(13/2)<--(4)F(3/2)-->(4)G(7/2) in the films generated avalanche upconversion emissions with a high slope of approximately 12.0, which could be due to the large avalanche cross relaxation rates and spectral broadening effect. In contrast, the spectral broadening effect in the NaNdF(4) NCs films increased the energy transfer (4)I(15/2)<--(4)F(3/2)-->(4)G(5/2) of the Nd(3+) ions, and induced a new upconversion emission at approximately 680 nm with the slope increased from 1.0 to 3.2.