Doped Upconversion Nanoparticles Research Articles

Tip-Enhanced Upconversion Luminescence in Yb3+–Er3+ Codoped NaYF4 Nanocrystals

Lanthanide doped upconversion nanoparticles reveal enormous potential for biomedical applications. However, they are limited by low upconversion efficiency. In this paper, we demonstrate tip-enhanced upconversion luminescence (UCL) from a single Yb3+–Er3+-codoped NaYF4 nanoparticle with a maximum enhancement factor of 11 by the plasmonic effect, which is a solution for improving the conversion efficiency and will become a potential technique for the applications in sensitive imaging and detection via speeding up both the absorption and the emission processes of lanthanide doped upconversion nanoparticles. By investigating the optical properties of the tip-enhanced UCL at 550 and 660 nm separately in Yb3+–Er3+-codoped NaYF4 nanoparticles, we observe that the gold-coated tip influences the upconversion process in Yb3+–Er3+-codoped NaYF4 particles by improving the reception and the transmission of incident electromagnetic fields.

Near infrared light mediated release of doxorubicin using upconversion nanoparticles.

Lanthanide doped upconversion nanoparticles grafted with a photocaged analog of doxorubicin allow near IR-release of doxorubicin.

Tunable chemical release from polyester thin film by photocatalytic zinc oxide and doped LiYF4 upconverting nanoparticles.

Once manufactured or implanted, polyester release kinetics tend to be fixed with little modulation possible for optimal local chemical concentrations. Here, a typical implantable polyester was fabricated into thin films (∼50 μm thick) with additives of photocatalytic ZnO nanoparticles, lanthanide-doped LiYF4 nanoparticle upconverting nanoparticles, or a combination thereof and irradiated with either 6 mW ultraviolet (365 nm) light emitting diodes or 50 mW near-infrared (980 nm) laser diodes to induce polymer photooxidation. Irradiated polyester films with the aforementioned photoadditives had enhanced release kinetics up to 30 times more than nonirradiated, neat films with extended release times of 28 days. Near-infrared, ZnO-mediated photocatalysis had the highest light on/light off ratio release kinetics of 15.4, while doped LiYF4 upconversion nanoparticles paired with ZnO nanoparticles had the highest linear R(2) correlation of 0.98 with respect to duty cycle and release kinetics. Future applications of the technology will aim toward modulation of previously developed polymeric reagents/drugs for real-time, feedback-optimized release.

Brain Tumors: Single Ho3+‐Doped Upconversion Nanoparticles for High‐Performance T2‐Weighted Brain Tumor Diagnosis and MR/UCL/CT Multimodal Imaging (Adv. Funct. Mater. 42/2014)

Brain Tumors: Single Ho³⁺‐Doped Upconversion Nanoparticles for High‐Performance <i>T</i>₂‐Weighted Brain Tumor Diagnosis and MR/UCL/CT Multimodal Imaging (Adv. Funct. Mater. 42/2014)

A facile synthesis of NaYF4:Yb3+/Er3+nanoparticles with tunable multicolor upconversion luminescence properties for cell imaging

The ability to manipulate the upconversion luminescence of lanthanide-ion doped fluoride upconversion nanoparticles (UCNPs) is critical and highly desired due to their wide applications in color displays, multiplexing bioassays and multicolor imaging. Here, we developed a facile strategy for simultaneously tuning color output and enhancing upconversion emission of Yb3+/Er3+ doped fluoride UCNPs, based on adjusting the crystalline phases and particle size. With the transformation of crystalline phases from α, a transition state of α mixed β, and finally to β phase, the upconversion emission color output changed from red, yellow, and finally turned green. That is, the UCNPs' emission is sensitive to the crystallite size and phase. Moreover, the fluorescence intensity of the obtained UCNPs became stronger with the crystalline phase changing from a to β. Three kinds of UCNPs including α-UCNPs, α mixed β-UCNPs, and β-UCNPs were used for cell imaging, while the transition state phase α mixed β-UCNPs was the better candidate.

Single Ho3+‐Doped Upconversion Nanoparticles for High‐Performance T2‐Weighted Brain Tumor Diagnosis and MR/UCL/CT Multimodal Imaging

Multimodal bio‐imaging has attracted great attention for early and accurate diagnosis of tumors, which, however, suffers from the intractable issues such as complicated multi‐step syntheses for composite nanostructures and interferences among different modalities like fluorescence quenching by MRI contrast agents (e.g., magnetic iron oxide NPs). Herein, the first example of T2‐weighted MR imaging of Ho3+‐doped upconversion nanoparticles (UCNPs) is presented, which, very attractively, could also be simultaneously used for upconversion luminesence (UCL) and CT imaging, thus enabling high performance multi‐modal MRI/UCL/CT imagings in single UCNPs. The new finding of T2‐MRI contrast enhancement by integrated sensitizer (Yb3+) and activator (Ho3+) in UCNPs favors accurate MR diagnosis of brain tumor and provides a new strategy for acquiring T2‐MRI/optical imaging without fluorescence quenching. Unlike other multi‐phased composite nanostructures for multimodality imaging, this Ho3+‐doped UCNPs are featured with simplicity of synthesis and highly efficient multimodal MRI/UCL/CT imaging without fluorescence quenching, thus simplify nanostructure and probe preparation and enable win–win multimodality imaging.

3-Dimensional photonic crystal surface enhanced upconversion emission for improved near-infrared photoresponse

The enhancement of upconversion luminescence of lanthanide-ion doped fluoride upconversion nanoparticles (UCNPs) is particularly important and highly required for their myriad applications in sensing, photoelectronic devices and bio-imaging. In this work, the amplification of luminescence in NaYF4:Yb/Er and NaYF4:Yb/Tm UCNPs in close proximity to the three-dimensional photonic crystal (3D PC) surface for improved near-infrared photoresponse of a carbon nanotube-based phototransistor is reported. The self-assembled opal 3D PCs with polystyrene sphere sizes of 200, 290 and 360 nm that exhibit reflection peaks of 450, 650 and 800 nm respectively were used for upconversion enhancement, and around 30 times enhancement was obtained for NaYF4:Yb/Er and NaYF4:Yb/Tm UCNPs. Time-resolved upconversion emission and 3D PC transmittance-dependent upconversion enhancement reveal that the enhanced absorption and the extraction effects, resulting from the enhanced non-resonant pump excitation field and the strong coherent scattering provided by 3D PCs respectively, are responsible for the large enhancement. As a proof-of-concept experiment, the prepared 3D PC/NaYF4:Yb/Tm UCNP coupled material layer was introduced into the carbon nanotube-based phototransistor. It is shown that the photoresponsivity of the device to near-infrared light was improved by 10 times with respect to the control device with carbon nanotubes only, which reveals the promising applications of this coupled material in photoelectronic devices such as photovoltaics and other types of phototransistors.

Functionalized Upconversion Nanoparticles: Versatile Nanoplatforms for Translational Research

The design, application, and translation of targeted multimodality molecular imaging probes based on nanotechnology have attracted increasing attentions during the last decade and will continue to play vital roles in cancer diagnosis and personalized medicine. With the growing awareness of drawbacks of traditional organic dyes and quantum dots, biocompatible lanthanide ion doped upconversion nanoparticles have emerged as promising candidates for clinically translatable imaging probes, owing to their unique features that are suitable for future targeted multimodal imaging in living subjects. In this review, we summarized the recent advances in the field of functionalized upconversion nanoparticles (f-UCNP) for biological imaging and therapy in vivo, and discussed the future research directions, obstacles ahead, and the potential use of f-UCNP in translational research.

Cysteine modified rare-earth up-converting nanoparticles for in vitro and in vivo bioimaging

Cysteine, as a small organic molecule and amino acid, is a basic building block for proteins and has special physiological functions in vivo. Cysteine has strong affinity for cells, which can be taken advantage for various applications. A new and facile surface modification method has been developed for rare-earth doped upconversion nanoparticles (UCNs) using cysteine. Compared with unmodified samples, the water-solubility and biocompatibility of the cysteine modified NaYF4:Yb,Er and NaYF4:Yb,Tm UCNs (termed as UCN-Er-Cys and UCN-Tm-Cys, respectively) have been significantly improved, while their particle size and emission properties did not change substantially. Due to the low cytotoxicity as revealed by methyl thiazolyl tetrazolium assay, the cysteine modified UCNs were successfully applied to imaging of Hela cells in vitro and nude mouse in vivo. Most significant is that the method offers the advantages of ease of synthesis and handling as well as potentially low cost for biomedical emerging applications.

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

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.

Approaches to the Multicolor Tuning of Lanthanide-Ion Doped Upconversion Nanoparticles

In recent years, lanthanide-ion doped nanocrystals have attracted considerable attention for its promising applications in multiplexed biological labeling. These materials can convert near-infrared (NIR) light into visible and offer low autofluorescence, high resistance to photobleaching, high penetration depth and large anti-Stokes shifts. With the development of these techniques, the ability to manipulate multicolor output has become more important for its biological and photovoltaic applications. This review mainly focuses on the recent development of various approaches for the multicolor tuning of lanthanide-ion doped upconversion nanoparticles.

Sensing using rare-earth-doped upconversion nanoparticles.

Optical sensing plays an important role in theranostics due to its capability to detect hint biochemical entities or molecular targets as well as to precisely monitor specific fundamental psychological processes. Rare-earth (RE) doped upconversion nanoparticles (UCNPs) are promising for these endeavors due to their unique frequency converting capability; they emit efficient and sharp visible or ultraviolet (UV) luminescence via use of ladder-like energy levels of RE ions when excited at near infrared (NIR) light that are silent to tissues. These features allow not only a high penetration depth in biological tissues but also a high detection sensitivity. Indeed, the energy transfer between UCNPs and biomolecular or chemical indicators provide opportunities for high-sensitive bio- and chemical-sensing. A temperature-sensitive change of the intensity ratio between two close UC bands promises them for use in temperature mapping of a single living cell. In this work, we review recent investigations on using UCNPs for the detection of biomolecules (avidin, ATP, etc.), ions (cyanide, mecury, etc.), small gas molecules (oxygen, carbon dioxide, ammonia, etc.), as well as for in vitro temperature sensing. We also briefly summarize chemical methods in synthesizing UCNPs of high efficiency that are important for the detection limit.

Multicolor tunability and upconversion enhancement of fluoride nanoparticles by oxygen dopant

The ability to manipulate the upconversion luminescence of lanthanide-ion doped fluoride upconversion nanoparticles (UCNPs) is particularly important and highly desired due to their wide applications in color displays, multiplexing bioassays and multicolor imaging. Here, we developed a strategy for simultaneously tuning color output and enhancing upconversion emission of Yb/Er doped fluoride UCNPs, based on adjusting the oxygen doping level. The synthesis of multicolored multifunctional NaGdF4:Yb,Er UCNPs was used as the model host system to demonstrate this protocol. Ammonium nitrate (NH4NO3) was used as the oxygen source and added into the reaction system at the beginning stage of nucleation and growth process of fluoride UCNPs, which facilitates the formation of enough oxygen atoms and the diffusion of these into the fluoride host matrix. The results revealed that multicolour output and upconversion enhancement mainly resulted from the variation of phonon energy and crystal field symmetry of the host lattice, respectively. This strategy can be further expanded to other fluoride host matrices. As an example of an application, multicolored UCNPs were used as a color converter in light emitting diodes, which can effectively convert near-infrared light into visible light. It is expected that these multicolored UCNPs will be promising for applications in multiplexing biodetection, bioimaging (optical and magnetic resonance imaging) and other optical technologies, and the present method for the control of O(2-) doping may also be used in other functional nanomaterials.

Water-soluble conjugated polyelectrolyte brush encapsulated rare-earth ion doped nanoparticles with dual-upconversion properties for multicolor cell imaging

A concise route to prepare water-soluble rare-earth ion doped upconversion nanoparticles (UCNPs) by encapsulation of grafted cationic conjugated polyelectrolyte brushes (PFNBr) is reported. Integrating two kinds of upconversion materials effectively addresses multicolor fluorescence by introducing the concept of dual-upconversion.

Positive and Negative Lattice Shielding Effects Co-existing in Gd (III) Ion Doped Bifunctional Upconversion Nanoprobes

Gadolinium (Gd) doped upconversion nanoparticles (UCNPs) have been well documented as T1-MR and fluorescent imaging agents. However, the performance of Gd3+ ions located differently in the crystal lattice still remains debatable. Here, a well-designed model was built based on a seed-mediated growth technique to systematically probe the longitudinal relaxivity of Gd3+ ions within the crystal lattice and at the surface of UCNPs. We found, for the first time, a nearly 100% loss of relaxivity of Gd3+ ions buried deeply within crystal lattices (> 4 nm), which we named a negative lattice shielding effect (n-LSE) as compared to the positive lattice shielding effect (p-LSE) for the enhanced upconversion fluorescent intensity. As-observed n-LSE was further found to be shell thickness dependent. By suppressing the n-LSE as far as possible, we optimized the UCNPs' structure design and achieved the highest r1 value (6.18 mM-1s-1 per Gd3+ ion) among previously reported counterparts. The potential bimodal imaging application both in vitro and in vivo of as-designed nano-probes was also demonstrated. This study clears the debate over the role of bulk and surface Gd3+ ions in MRI contrast imaging and paves the way for modulation of other Gd-doped nanostructures for highly efficient T1-MR and upconversion fluorescent bimodal imaging.

Multicolor output and shape controlled synthesis of lanthanide-ion doped fluorides upconversion nanoparticles

A general and facile approach for tailoring the multicolor output and shapes of lanthanide-ion doped fluoride upconversion nanoparticles (UCNPs) within a given composition is presented. By adjusting the temperature and time in the thermolysis procedure, the color output and shapes of NaYF(4):20%Yb, 2%Er UCNPs can be readily manipulated. The nanoparticles were characterized through the use of transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and upconversion luminescence spectroscopy. It is shown that the relative intensities of green emissions gradually increased with the rise of temperature and prolongation of growth time under excitation of 980 nm, which resulted in multicolor output of NaYF(4):20%Yb, 2%Er UCNPs. Simultaneously, the shapes for UCNPs can also be controlled. TEM images, estimated micro-stress by Williamson-Hall methodology and a series of control experiments and analyses reveal that crystallinity is mainly responsible for the multicolor output of UCNPs. Based on the above method, the tailoring of color output is also successfully realized in Ho(3+) and Tm(3+) ions. It is expected that this method may be used to tune the physical properties of other nanoparticles, and these multicolored UCNPs are promising for applications in multiplexed bioimaging, biodetection, display, other optical technologies, etc.

A facile and general approach for the multicolor tuning of lanthanide-ion doped NaYF4 upconversion nanoparticles within a fixed composition

In this paper, we report a general and facile approach for subtly tuning the multicolor output of lanthanide-ion doped NaYF4 upconversion nanoparticles (UCNPs) within a given composition under single wavelength excitation of 980 nm. By adjusting the molar ratio of octadecylamine (OM) and oleamide in reaction solution under a thermolysis procedure, the color output of NaYF4:20%Yb,2%Er UCNPs can be fine tuned. X-Ray diffraction (XRD), transmission electron microscopy (TEM), upconversion photoluminescence spectroscopy, FT-IR and 1H-NMR were employed to characterize the obtained samples. 1H-NMR analysis and a series of control experiments have revealed that the tunability of multicolor output mainly resulted from different ratios of two coordinating ligands bonded onto the particle surface. We also synthesized NaYF4:20%Yb,2%Er UCNPs with multicolor output in three pairs of mixtures, namely OM and oleic acid (OA), OM and N-octadecyloleamide (OOA), as well as OA and OOA, based on the above method. Moreover, this approach was further extended to the preparation of multicolored NaYF4:20%Yb,2%Ho and NaYF4:20%Yb,0.5%Tm UCNPs. It is expected these multicolored UCNPs have great potential for applications in biology, displays and other optical technologies.

Synthesis of colour tunable lanthanide-ion doped NaYF4 upconversion nanoparticles by controlling temperature

A simple and general method is reported to tune the multicolour output of lanthanide-ion doped NaYF(4) upconversion nanoparticles within a given composition by controlling the reaction temperature in the thermolysis procedure.