Showing papers by "Xueyuan Chen published in 2015"

Lanthanide-doped upconversion nano-bioprobes: electronic structures, optical properties, and biodetection

Abstract: Lanthanide-doped upconversion nanoparticles (UCNPs) have attracted considerable interest due to their superior physicochemical features, such as large anti-Stokes shifts, low autofluorescence background, low toxicity and high penetration depth, which make them extremely suitable for use as alternatives to conventional downshifting luminescence bioprobes like organic dyes and quantum dots for various biological applications. A fundamental understanding of the photophysics of lanthanide-doped UCNPs is of vital importance for discovering novel optical properties and exploring their new applications. In this review, we focus on the most recent advances in the development of lanthanide-doped UCNPs as potential luminescent nano-bioprobes by means of our customized lanthanide photophysics measurement platforms specially designed for upconversion luminescence, which covers from their fundamental photophysics to bioapplications, including electronic structures (energy levels and local site symmetry of emitters), excited-state dynamics, optical property designing, and their promising applications for in vitro biodetection of tumor markers. Some future prospects and efforts towards this rapidly growing field are also envisioned.

Poly(Acrylic Acid) Modification of Nd3+-Sensitized Upconversion Nanophosphors for Highly Efficient UCL Imaging and pH-Responsive Drug Delivery

Abstract: In this work, a simple method is demonstrated for the synthesis of multifunctional core-shell nanoparticles nayf4:yb,er@nayf4:yb@nandf4:yb@nayf4:yb@paa (labeled as er@y@nd@y@paa or ucnp@paa), which contain a highly effective 808-nm-to-visible ucnp core and a thin shell of poly(acrylic acid) (paa) to achieve upconversion bioimaging and ph-sensitive anticancer chemotherapy simultaneously. the core-shell nd3+-sensitized ucnps are optimized by varying the shell number, core size, and host lattices. the final optimized er@y@nd@y nanoparticle composition shows a significantly improved upconversion luminescence intensity, that is, 12.8 times higher than er@y@nd nanoparticles. after coating the nanocomposites with a thin layer of paa, the resulting ucnp@paa nanocomposite perform well as a ph-responsive nanocarrier and show clear advantages over ucnp@msio(2), which are evidenced by in vitro/in vivo experiments. histological analysis also reveals that no pathological changes or inflammatory responses occur in the heart, lungs, kidneys, liver, and spleen. in summary, this study presents a major step forward towards a new therapeutic and diagnostic treatment of tumors by using 808-nm excited ucnps to replace the traditional 980-nm excitation.

Multifunctional Nano‐Bioprobes Based on Rattle‐Structured Upconverting Luminescent Nanoparticles

Abstract: Lanthanide-doped upconversion nanoparticles (UCNPs) have shown great promise in versatile bioapplications. For the first time, organosilica-shelled β-NaLuF4:Gd/Yb/Er nanoprobes with a rattle structure have been designed for dual-modal imaging and photodynamic therapy (PDT). Benefiting from the unique rattle structure and aromatic framework, these nanoprobes are endowed with a high loading capacity and the disaggregation effect of photosensitizers. After loading of β-carboxyphthalocyanine zinc or rose Bengal into the nanoprobes, we achieved higher energy transfer efficiency from UCNPs to photosensitizers as compared to those with conventional core–shell structure or with pure-silica shell, which facilitates a large production of singlet oxygen and thus an enhanced PDT efficacy. We demonstrated the use of these nanoprobes in proof-of-concept X-ray computed tomography (CT) and UC imaging, thus revealing the great potential of this multifunctional material as an excellent nanoplatform for cancer theranostics.

Synergetic Spin Crossover and Fluorescence in One‐Dimensional Hybrid Complexes

Abstract: Hybrid materials integrated with a variety of physical properties, such as spin crossover (SCO) and fluorescence, may show synergetic effects that find applications in many fields. Herein we demonstrate a promising post-synthetic approach to achieve such materials by grafting fluorophores (1-pyrenecarboxaldehyde and Rhodamine B) on one-dimensional SCO FeII structures. The resulting hybrid materials display expected one-step SCO behavior and fluorescent properties, in particular showing a coupling between the transition temperature of SCO and the temperature where the fluorescent intensity reverses. Consequently, synergetic effect between SCO and fluorescence is incorporated into materials despite different fluorophores. This study provides an effective strategy for the design and development of novel magnetic and optical materials.

Lanthanide-doped luminescent nano-bioprobes for the detection of tumor markers

Abstract: Sensitive and specific biodetection of tumor markers is essential for early-stage cancer diagnosis and therapy, and will ultimately increase the patient survival rate. As a new generation of luminescent bioprobes, lanthanide (Ln3+)-doped inorganic luminescent nanoparticles have attracted considerable interest for a variety of biomedical applications due to their superior physicochemical properties. In this feature article, we provide a brief overview of the most recent advances in the development of Ln3+-doped luminescent nano-bioprobes and their promising applications for in vitro detection of tumor markers with an emphasis on the establishment of state-of-the-art assay techniques, such as heterogeneous time-resolved (TR) luminescent bioassay, dissolution-enhanced luminescent bioassay, upconversion (UC) luminescent bioassay, homogeneous TR Forster resonance energy transfer (TR-FRET) and UC-FRET bioassays. Some future prospects and efforts towards this emerging field are also envisioned.

Single-composition white-emitting NaSrBO3:Ce3+,Sm3+,Tb3+ phosphors for NUV light-emitting diodes

Abstract: Single-composition (or single-phase) phosphors have been proposed as a new strategy to overcome the concerns of emission reabsorption and different degradation rates of the three primary phosphors for light-emitting diode (LED) applications. A series of Ce3+, Sm3+ and Tb3+ co-doped NaSrBO3 phosphors were synthesized via a high temperature solid-state reaction. Upon near ultraviolet (NUV) excitation, tunable emission from violet to white in the visible region was realized in NaSrBO3:Ce3+,Sm3+,Tb3+ phosphors by controlling the dopant concentrations. Particularly, highly efficient white-light emission with a quantum yield as high as 48.2% was achieved. The energy transfer mechanism between Ce3+ and Sm3+ ions in NaSrBO3 was found to be predominantly of dipole–dipole nature. Moreover, the thermal quenching effect on the photoluminescence of NaSrBO3:Ce3+,Sm3+,Tb3+ was comprehensively surveyed over the range of 300–600 K, showing a good thermal stability for LED applications. By integrating this single-composition white-emitting NaSrBO3:Ce3+,Sm3+,Tb3+ phosphor with a 360 nm NUV chip, we fabricated a high-performance white LED (WLED), which exhibited an excellent color rendering index Ra of 80.1 and a correlated color temperature of 6731 K with CIE coordinates of (0.311, 0.314). These findings demonstrate that the proposed single-composition white-emitting NaSrBO3:Ce3+,Sm3+,Tb3+ phosphors can serve as promising phosphors for NUV-excited WLEDs.

A New Cubic Phase for a NaYF4 Host Matrix Offering High Upconversion Luminescence Efficiency

Abstract: A NaYF4 host matrix with a new cubic phase is fabricated to offer high upconversion luminescence efficiency. The new cubic phase is formed through a hexagonal-to-cubic phase transition by shining intense near-infrared light on lanthanide-doped hexagonal NaYF4 materials.

Lanthanide-doped semiconductor nanocrystals: electronic structures and optical properties

Abstract: Trivalent lanthanide (Ln3+) ions doped semiconductor nanomaterials have recently attracted considerable attention owing to their distinct optical properties and their important applications in diverse fields such as optoelectronic devices, flat plane displays and luminescent biolabels. This review provides a comprehensive survey of the latest advances in the synthesis, electronic structures and optical spectra of Ln3+ ions in wide band-gap semiconductor nanocrystals (SNCs). In particular, we highlight the general wet-chemical strategies to introduce Ln3+ ions into host lattices, the local environments as well as the sensitization mechanism of Ln3+ in SNCs. The energy levels and crystal-field parameters of Ln3+ in various SNCs determined from energy-level-fitting are summarized, which is of vital importance to understanding the optical properties of Ln3+ ions in SNCs. Finally, some future prospects and challenges in this rapidly growing field are also proposed.

Plasmon-induced hyperthermia: hybrid upconversion NaYF4:Yb/Er and gold nanomaterials for oral cancer photothermal therapy

Abstract: Nanocomposites consisting of upconversion nanoparticles (UCPs) and plasmonic materials have been widely explored for bio-imaging and cancer photothermal therapy (PTT). However, several challenges, including incomprehensible efficiency of energy transfer processes and optimization of the conditions for plasmon-induced photothermal effects, still exist. In this study, we fabricated NaYF4:Yb3+/Er3+ nanoparticles (NPs) conjugated with gold nanomaterials (Au NMs), such as Au NPs and gold nanorods (Au NRs). NaYF4:Yb3+/Er3+ NPs were used as photoconverters, which could emit green and red light under excitation of a 980 nm laser; Au NPs and Au NRs were also prepared and used as heat producers. The silica shell was further coated around UCPs to improve biocompatibility and as a bridge linking UCPs and the Au NMs. Most importantly, the thickness of the silica shell was tuned precisely to investigate the effective distance of the plasmonic field for heat induction. Energy transfer was confirmed by the declining UCL photoluminescence and emission decay time after connecting to the Au NMs. Moreover, a simulative model was built using the finite element method to assess the differences in heat generation between UCP@SiO2-NPs and UCP@SiO2-NRs. The surfaces of the hybrid nanocomposites were modified with folic acid to improve the specific targeting to cancer cells. The performance of the modified hybrid nanocomposites in PTT for OECM-1 oral cancer cells was evaluated.

Inorganic lanthanide nanoprobes for background-free luminescent bioassays

Abstract: Luminescent bioassay techniques have been widely adopted in a variety of research and medical institutions. However, conventional luminescent bioassays utilizing traditional bioprobes like organic dyes and quantum dots often suffer from the interference of background noise from scattered lights and autofluorescence from biological matrices. To eliminate this disadvantage, the use of inorganic lanthanide (Ln3+)-doped nanoparticles (NPs) is an excellent option in view of their superior optical properties, such as the long-lived downshifting luminescence, near-infrared triggered anti-Stokes upconverting luminescence and excitation-free persistent luminescence. In this review, we summarize the latest advances in the development of inorganic Ln3+-doped NPs as sensitive luminescent bioprobes from their fundamental physicochemical properties to biodetection, including the chemical synthesis, surface functionalization, optical properties and their promising applications for background-free luminescent bioassays. Future efforts and prospects towards this rapidly growing field are also proposed.

Three reversible polymorphic copper(I) complexes triggered by ligand conformation: insights into polymorphic crystal habit and luminescent properties.

Abstract: Three luminescent polymorphs based on a new copper(I) complex Cu(2-QBO)(PPh3)PF6 (1, PPh3 = triphenylphosphine, 2-QBO = 2-(2′-quinolyl)benzoxazole) have been synthesized and characterized by FT-IR, UV–vis, elemental analyses, and single-crystal X-ray diffraction analyses. Each polymorph can reversibly convert from one to another through appropriate procedures. Interestingly, such interconversion can be distinguished by their intrinsic crystal morphologies and colors (namely α, dark yellow plate, β, orange block, γ, light yellow needle) as well as photoluminescent (PL) properties. X-ray crystal structure analyses of these three polymorphs show three different supramolecular structures from 1D to 3D, which are expected to be responsible for the formation of three different crystal morphologies such as needle, plate, and block. Combination of the experimental data with DFT calculations on these three polymorphs reveals that the polymorphic interconversion is triggered by the conformation isomerization of the...

Persistent luminescence from Eu3+ in SnO2 nanoparticles

Abstract: Persistent luminescence phosphors, which are capable of emitting light for a long time after ceasing excitation, have shown great promise in diverse areas as bioprobes, lighting and displays. Exploring new materials to realize efficient persistent luminescence is a goal of general concern. Herein, we report a novel persistent luminescence phosphor based on Eu3+-doped SnO2 nanoparticles (NPs). The afterglow decay behaviour, the trap depth distribution as well as the underlying mechanism for persistent luminescence of the NPs were comprehensively surveyed by means of thermoluminescence and temperature-dependent afterglow decay measurements. It was found that the thermal activation mechanism is responsible for the afterglow decay of the NPs with an inverse power-law exponent of 1.0 (or 1.7) in the temperature region below (or above) 220 K. In particular, the co-existence of uniform and exponential distributions in trap depths may result in such a unique afterglow decay behaviour. These results reveal the great potential of SnO2 NPs as an excellent host material for Eu3+ doping for the generation of efficient persistent luminescence.

Time‐Resolved Luminescent Biosensing Based on Inorganic Lanthanide‐Doped Nanoprobes

Abstract: Time-resolved (TR) photoluminescence (PL) biosensing has been widely adopted in many research and medical institutions. However, commercial molecular TRPL bioprobes like lanthanide (Ln3+)-chelates suffer from poor photochemical stability and long-term toxicity. Inorganic Ln3+-doped nanocrystals (NCs), owing to their superior physicochemical properties over Ln3+-chelates, are regarded as a new generation of luminescent nanoprobes for TRPL biosensing. The long-lived PL of Ln3+-doped NCs combined with the TRPL technique is able to completely suppress the interference of the short-lived background, resulting in a background-free signal and therefore a remarkable sensitivity for biosensing. In this feature article, we summarize the latest advancements in inorganic Ln3+-doped NCs as TRPL nano-bioprobes from their fundamental optical properties to their potential applications for ultrasensitive biodetection and high-resolution bioimaging. Future efforts towards the commercialization of these nanoprobes are also proposed.

Reply to Comment on “Breakdown of Crystallographic Site Symmetry in Lanthanide‐Doped NaYF4 Crystals”

Abstract: Karbowiak et al. recently commented on our Communication “Breakdown of Crystallographic Site Symmetry in Lanthanide-Doped NaYF4 Crystals”. [1] They attempted to criticize the crystal-field (CF) analysis of Eu in disordered NaYF4 based on their surmise. Unfortunately, there are numerous misunderstandings in their correspondence. In this reply, we respond to their comment and clarify our interpretations of the issues they raised. Regarding the adoption of the CF parameters (CFPs) of Eu in Gd2O3 as the starting values in the fit, it is true that the coordination environments of Gd2O3 and NaYF4 host are somewhat different. However, it should be pointed out that both aand b-NaYF4 are disordered crystals, where the site symmetry of Y isOh and C3h, respectively. [3] Once Eu ions are doped into such disordered crystals to substitute for Y, the symmetry of spectroscopic sites of Eu may differ drastically from that of crystallographic sites of Y, which is due to the mismatch of ionic radius between Eu and Y. The local site symmetry of Eu in NaYF4 can be revealed by the high-resolution emission spectra (Figure 1), selective excitation spectra, and photoluminescence (PL) decays at low temperature (Supporting Information, Figure S1). Note that our emission pattern of b-NaYF4:Eu 3+ is consistent with that reported by other groups. For instance, the line positions and splittings reported by Jia et al. are nearly identical to our results (Figure 1). In the PL pattern, the most crucial fingerprint to corroborate the low site symmetry in NaYF4:Eu 3+ crystals is the appearance of the D0!F0 peak. Furthermore, three and five CF transition lines of D0 to F1 and F2 were observed, which demonstrated the highest site symmetry of Eu in b-NaYF4, distorted from C3h, should be Cs. Such breakdown of crystallographic site symmetry in Eu-doped NaYF4 crystals was not only corroborated by these PL spectra, but also confirmed by the CF level fitting. To the best of our knowledge, until now no data on the CFPs of NaYF4 or other disordered crystals with similar structure and local site symmetry are available. The choice of the set of CFPs values of Gd2O3 as the starting ones in the fit is technically feasible based on the following considerations. First, as mentioned in Ref. [1], the highest spectroscopic site symmetries of Eu are found to descend from crystallographic Oh to Cs (or C2) in a-NaYF4, and from crystallographic C3h to Cs in b-NaYF4, respectively. Similar to the wellestablished CFP fitting strategy in this field, to rationally reduce the number of freely varied CFPs in the fit, we performed the energy level fitting by reasonably assuming the highest site symmetry of Cs for both aand b-NaYF4 in view of the same set of allowed CFPs for the site symmetry of Cs or C2. [7] Second, by using the CFPs of Gd2O3:Eu 3+ as starting values, the energy-level fitting yielded a relatively small root-mean-square deviations for aand b-NaYF4, namely, 13.5 and 13.8 cm 1 (with energy shifts in a range of 0–30 cm 1 for most of the levels), respectively, an important indicator for the goodness of the fit. Note that total 48 CF levels of Eu in a-NaYF4, instead of 41 levels as they criticized in their comment, were included in our fit. Figure 1. 10 K PL emission spectra of b-NaYF4:Eu 3+ reported in Ref. [5a] (upper) and our original work (lower), respectively. The CF transition line from D0 to F0 is marked by an asterisk.

Plasmon-Modulated polarized upconversion emissions from single gold nanorod-nanophosphors hybrid nanostructures

Abstract: We demonstrate plasmon-modulated polarized upconversion emissions from single gold nanorod@SiO2@CaF2:Yb3+,Er3+ hybrid core-shell nanostructures. By varying the SiO2 spacer thickness, the polarization state and photoluminescence intensity of green and red emissions can be flexibly tuned.