Showing papers by "Xiaogang Liu published in 2015"

Stabilizing triplet excited states for ultralong organic phosphorescence

Abstract: The control of the emission properties of synthetic organic molecules through molecular design has led to the development of high-performance optoelectronic devices with tunable emission colours, high quantum efficiencies and efficient energy/charge transfer processes. However, the task of generating excited states with long lifetimes has been met with limited success, owing to the ultrafast deactivation of the highly active excited states. Here, we present a design rule that can be used to tune the emission lifetime of a wide range of luminescent organic molecules, based on effective stabilization of triplet excited states through strong coupling in H-aggregated molecules. Our experimental data revealed that luminescence lifetimes up to 1.35 s, which are several orders of magnitude longer than those of conventional organic fluorophores, can be realized under ambient conditions. These results outline a fundamental principle to design organic molecules with extended lifetimes of excited states, providing a major step forward in expanding the scope of organic phosphorescence applications.

Controlling upconversion nanocrystals for emerging applications

Abstract: Lanthanide-doped upconversion nanocrystals enable anti-Stokes emission with pump intensities several orders of magnitude lower than required by conventional nonlinear optical techniques. Their exceptional properties, namely large anti-Stokes shifts, sharp emission spectra and long excited-state lifetimes, have led to a diversity of applications. Here, we review upconversion nanocrystals from the perspective of fundamental concepts and examine the technical challenges in relation to emission colour tuning and luminescence enhancement. In particular, we highlight the advances in functionalization strategies that enable the broad utility of upconversion nanocrystals for multimodal imaging, cancer therapy, volumetric displays and photonics.

Temporal full-colour tuning through non-steady-state upconversion

Abstract: Developing light-harvesting materials with tunable emission colours has always been at the forefront of colour display technologies. The variation in materials composition, phase and structure can provide a useful tool for producing a wide range of emission colours, but controlling the colour gamut in a material with a fixed composition remains a daunting challenge. Here, we demonstrate a convenient, versatile approach to dynamically fine-tuning emission in the full colour range from a new class of core-shell upconversion nanocrystals by adjusting the pulse width of infrared laser beams. Our mechanistic investigations suggest that the unprecedented colour tunability from these nanocrystals is governed by a non-steady-state upconversion process. These findings provide keen insights into controlling energy transfer in out-of-equilibrium optical processes, while offering the possibility for the construction of true three-dimensional, full-colour display systems with high spatial resolution and locally addressable colour gamut.

Recent advances in C–S bond formation via C–H bond functionalization and decarboxylation

Abstract: The development of mild and general methods for C–S bond formation has received significant attention because the C–S bond is indispensable in many important biological and pharmaceutical compounds. Early examples for the synthesis of C–S bonds are generally limited to the condensation reaction between a metal thiolate and an organic halide. Recent chemical approaches for C–S bond formation, based upon direct C–H bond functionalization and decarboxylative reactions, not only provide new insights into the mechanistic understanding of C–S coupling reactions but also allow the synthesis of sulfur-containing compounds from more effective synthetic routes with high atom economy. This review intends to explore recent advances in C–S bond formation via C–H functionalization and decarboxylation, and the growing opportunities they present to the construction of complex chemical scaffolds for applications encompassing natural product synthesis, synthetic methodology development, and functional materials as well as nanotechnology.

Photon upconversion nanomaterials

Abstract: Photon upconversion through the use of lanthanide-doped materials has been the focus of a growing body of research in the fields of materials chemistry and physics for more than 50 years. The attraction of this field has been the ability to generate photons at shorter wavelengths than the excitation wavelength after laser stimulation. Despite its potential utility for a number of applications, photon upconversion has been primarily investigated in bulk glasses or crystalline materials. That situation dramatically changed in the mid-2000s, with the widespread research in the development of upconversion nanomaterials. As a unique class of optical materials, upconversion nanomaterials exhibit useful applications spanning from lighting to volumetric 3D displays to photovoltaics. Particularly, nanosized upconversion nanocrystals have proven valuable as luminescent labels for chemical and biological sensing with marked improvements in the sensitivity and versatility of the sensors. Recent advances in the field of upconversion nanomaterials have motivated us to initiate a thematic issue focusing on fundamental principles, synthetic strategies, materials characterization, broad applications, and a Department of Chemistry, National University of Singapore, Singapore 117543, Singapore. E-mail: chmlx@nus.edu.sg b Institute of Materials Research and Engineering, Agency for Science, Technology and Research, Singapore 117602, Singapore c Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, PKU-HKU Joint Laboratory in Rare Earth Materials and Bioinorganic Chemistry, Peking University, Beijing 100871, China. E-mail: yan@pku.edu.cn d Department of Chemistry and Biochemistry and Centre for NanoScience Research, Concordia University, Montreal, Quebec, H4B 1R6, Canada. E-mail: john.capobianco@concordia.ca † Part of the photon upconversion nanomaterials themed issue.

High-efficiency in vitro and in vivo detection of Zn2+ by dye-assembled upconversion nanoparticles.

Abstract: Development of highly sensitive and selective sensing systems of divalent zinc ion (Zn2+) in organisms has been a growing interest in the past decades owing to its pivotal role in cellular metabolism, apoptosis, and neurotransmission. Herein, we report the rational design and synthesis of a Zn2+ fluorescent-based probe by assembling lanthanide-doped upconversion nanoparticles (UCNPs) with chromophores. Specifically, upconversion luminescence (UCL) can be effectively quenched by the chromophores on the surface of nanoparticles via a fluorescence resonant energy transfer (FRET) process and subsequently recovered upon the addition of Zn2+, thus allowing for quantitative monitoring of Zn2+. Importantly, the sensing system enables detection of Zn2+ in real biological samples. We demonstrate that this chromophore–UCNP nanosystem is capable of implementing an efficient in vitro and in vivo detection of Zn2+ in mouse brain slice with Alzheimer’s disease and zebrafish, respectively.

Co3O4 nanoparticles decorated carbon nanofiber mat as binder-free air-cathode for high performance rechargeable zinc-air batteries

Abstract: An efficient, durable and low cost air-cathode is essential for a high performance metal-air battery for practical applications. Herein, we report a composite bifunctional catalyst, Co3O4 nanoparticles-decorated carbon nanofibers (CNFs), working as an efficient air-cathode in high performance rechargeable Zn-air batteries (ZnABs). The particles-on-fibers nanohybrid materials were derived from electrospun metal-ion containing polymer fibers followed by thermal carbonization and a post annealing process in air at a moderate temperature. Electrochemical studies suggest that the nanohybrid material effectively catalyzes oxygen reduction reaction via an ideal 4-electron transfer process and outperforms Pt/C in catalyzing oxygen evolution reactions. Accordingly, the prototype ZnABs exhibit a low discharge–charge voltage gap (e.g. 0.7 V, discharge–charge at 2 mA cm−2) with higher stability and longer cycle life compared to their counterparts constructed using Pt/C in air-cathode. Importantly, the hybrid nanofiber mat readily serves as an integrated air-cathode without the need of any further modification. Benefitting from its efficient catalytic activities and structural advantages, particularly the 3D architecture of highly conductive CNFs and the high loading density of strongly attached Co3O4 NPs on their surfaces, the resultant ZnABs show significantly improved performance with respect to the rate capability, cycling stability and current density, promising good potential in practical applications.

Probing the nature of upconversion nanocrystals: instrumentation matters

Abstract: Probing the nature of nanocrystalline materials such as the surface state, crystal structure, morphology, composition, optical and magnetic characteristics is a crucial step in understanding their chemical and physical performance and in exploring their potential applications. Upconversion nanocrystals have recently attracted remarkable interest due to their unique nonlinear optical properties capable of converting incident near-infrared photons to visible and even ultraviolet emissions. These optical nanomaterials also hold great promise for a broad range of applications spanning from biolabeling to optoelectronic devices. In this review, we overview the instrumentation techniques commonly utilized for the characterization of upconversion nanocrystals. A considerable emphasis is placed on the analytical tools for probing the optical properties of the luminescent nanocrystals. The advantages and limitations of each analytical technique are compared in an effort to provide a general guideline, allowing optimal conditions to be employed for the characterization of such nanocrystals. Parallel efforts are devoted to new strategies that utilize a combination of advanced emerging tools to characterize such nanosized phosphors.

Lanthanide-doped upconversion nanoparticles

Abstract: A new class of nanomaterials that convert near-IR radiation into tunable visible light has important implications for many fields of science and technology

Quantitatively Mapping Cellular Viscosity with Detailed Organelle Information via a Designed PET Fluorescent Probe

Abstract: Viscosity is a fundamental physical parameter that influences diffusion in biological processes. The distribution of intracellular viscosity is highly heterogeneous, and it is challenging to obtain a full map of cellular viscosity with detailed organelle information. In this work, we report 1 as the first fluorescent viscosity probe which is able to quantitatively map cellular viscosity with detailed organelle information based on the PET mechanism. This probe exhibited a significant ratiometric fluorescence intensity enhancement as solvent viscosity increases. The emission intensity increase was attributed to combined effects of the inhibition of PET due to restricted conformational access (favorable for FRET, but not for PET), and the decreased PET efficiency caused by viscosity-dependent twisted intramolecular charge transfer (TICT). A full map of subcellular viscosity was successfully constructed via fluorescent ratiometric detection and fluorescence lifetime imaging; it was found that lysosomal regions in a cell possess the highest viscosity, followed by mitochondrial regions.

Photon Upconversion Through Tb3+‐Mediated Interfacial Energy Transfer

Abstract: A strategy of interfacial energy transfer upconversion is demonstrated through the use of a terbium (Tb(3+) ) dopant as energy donor or energy migrator in core-shell-structured nanocrystals. This mechanistic investigation presents a new pathway for photon upconversion, and, more importantly, contributes to the better control of energy transfer at the nanometer length scale.

Intracellular Adenosine Triphosphate Deprivation through Lanthanide-Doped Nanoparticles.

Abstract: Growing interest in lanthanide-doped nanoparticles for biological and medical uses has brought particular attention to their safety concerns. However, the intrinsic toxicity of this new class of optical nanomaterials in biological systems has not been fully evaluated. In this work, we systematically evaluate the long-term cytotoxicity of lanthanide-doped nanoparticles (NaGdF4 and NaYF4) to HeLa cells by monitoring cell viability (mitochondrial activity), adenosine triphosphate (ATP) level, and cell membrane integrity (lactate dehydrogenase release), respectively. Importantly, we find that ligand-free lanthanide-doped nanoparticles induce intracellular ATP deprivation of HeLa cells, resulting in a significant decrease in cell viability after exposure for 7 days. We attribute the particle-induced cell death to two distinct cell death pathways, autophagy and apoptosis, which are primarily mediated via the interaction between the nanoparticle and the phosphate group of cellular ATP. The understanding gained f...

Energy Migration Upconversion in Manganese(II)-Doped Nanoparticles

Abstract: We report the synthesis and characterization of cubic NaGdF4:Yb/Tm@NaGdF4:Mn core-shell structures. By taking advantage of energy transfer through Yb→Tm→Gd→Mn in these core-shell nanoparticles, we have realized upconversion emission of Mn(2+) at room temperature in lanthanide tetrafluoride based host lattices. The upconverted Mn(2+) emission, enabled by trapping the excitation energy through a Gd(3+) lattice, was validated by the observation of a decreased lifetime from 941 to 532 μs in the emission of Gd(3+) at 310 nm ((6)P(7/2)→(8)S(7/2)). This multiphoton upconversion process can be further enhanced under pulsed laser excitation at high power densities. Both experimental and theoretical studies provide evidence for Mn(2+) doping in the lanthanide-based host lattice arising from the formation of F(-) vacancies around Mn(2+) ions to maintain charge neutrality in the shell layer.

Subwavelength imaging through ion-beam-induced upconversion

Abstract: The combination of an optical microscope and a luminescent probe plays a pivotal role in biological imaging because it allows for probing subcellular structures. However, the optical resolutions are largely constrained by Abbe's diffraction limit, and the common dye probes often suffer from photobleaching. Here we present a new method for subwavelength imaging by combining lanthanide-doped upconversion nanocrystals with the ionoluminescence imaging technique. We experimentally observed that the ion beam can be used as a new form of excitation source to induce photon upconversion in lanthanide-doped nanocrystals. This approach enables luminescence imaging and simultaneous mapping of cellular structures with a spatial resolution of sub-30 nm.

Bivariate Genome-Wide Association Study Implicates ATP6V1G1 as a Novel Pleiotropic Locus Underlying Osteoporosis and Age at Menarche.

Abstract: Objective: Age at menarche (AAM) is determined by the overall duration of endocrine-tissue sex hormone exposure levels. Osteoporosis, the most common metabolic bone disease, is characterized primarily by reduced bone mineral density (BMD) and an increased risk of low trauma fractures. Bone was an endocrine organ regulating the synthesis and secretion of sex steroid hormones. The mutual dependence between bone and gonads underscore the importance of genetic approaches to identify novel pleiotropic genetic factors coregulating BMD and AAM. In this study, we performed a bivariate genome-wide association study (GWAS) to explore novel ethnic common loci and/or genes that may influence both AAM and BMD. Methods: We analyzed genotyping data available for 826 unrelated Chinese subjects using genome-wide human genotyping arrays. After quality control, a total of 702 413 single-nucleotide polymorphisms (SNPs) were tested for association using a bivariate linear regression model. The interesting SNPs were replicated...

Enhancing Luminescence in Lanthanide-Doped Upconversion Nanoparticles

Abstract: The enthusiasm for research on lanthanide-doped upconversion nanoparticles is driven by both a fundamental interest in the optical properties of lanthanides embedded in different host lattices and their promise for broad applications ranging from biological imaging to photodynamic therapy. Despite the considerable progress made in the past decade, the field of upconversion nanoparticles has been hindered by significant experimental challenges associated with low upconversion conversion efficiencies. Recent experimental and theoretical studies on upconversion nanoparticles have, however, led to the development of several effective approaches to enhancing upconversion luminescence, which could have profound implications for a range of applications. Herein we present the underlying principles of controlling energy transfer through lanthanide doping, overview the major advances and key challenging issues in improving upconversion luminescence, and consider the likely directions of future research in the field.

Coumarin 545: an emission reference dye with a record-low temperature coefficient for ratiometric fluorescence based temperature measurements

Abstract: The emission intensities of coumarin 545 solution exhibit a low temperature dependence, with a record-low temperature coefficient of only ∼0.025% per °C. This monomer-aggregate coupled fluorescence system can be used for ratiometric temperature measurements with high spatial and temporal resolutions; three different working modes have been demonstrated.

Recent Advances in C—S Bond Formation via C—H Bond Functionalization and Decarboxylation

Abstract: The development of mild and general methods for C–S bond formation has received significant attention because the C–S bond is indispensable in many important biological and pharmaceutical compounds. Early examples for the synthesis of C–S bonds are generally limited to the condensation reaction between a metal thiolate and an organic halide. Recent chemical approaches for C–S bond formation, based upon direct C–H bond functionalization and decarboxylative reactions, not only provide new insights into the mechanistic understanding of C–S coupling reactions but also allow the synthesis of sulfur-containing compounds from more effective synthetic routes with high atom economy. This review intends to explore recent advances in C–S bond formation via C–H functionalization and decarboxylation, and the growing opportunities they present to the construction of complex chemical scaffolds for applications encompassing natural product synthesis, synthetic methodology development, and functional materials as well as nanotechnology.

Supramolecular polymers: Chain growth in control.

Abstract: Supramolecular polymerizations typically proceed through stepwise intermolecular mechanisms, concomitant with many side reactions to yield aggregates of unpredictable size, shape and mass. Now, a chain-growth strategy is shown to allow assembly of molecules into supramolecular chain structures endowed with precisely controlled characteristics.

Catalytic behavior and synergistic effect of nonthermal plasma and CuO/AC catalyst for benzene destruction

Abstract: Nonthermal plasma-catalysis hybrid technology (NTP-C) operated at ambient temperature and pressure offers an innovative and effective approach to solving the problem of dilute volatile organic compounds pollution. Herein, the destruction of benzene (50–450 ppm) over an in-plasma NTP-C composite system was investigated. The AO x /active carbon (AO x /AC), AO x /3A molecular sieve (AO x /MS), and AO x /γ-Al2O3 (A = Fe, Ag, Zn, Mn, and Cu) catalysts were prepared by the incipient-wetness impregnation method. The destruction performances of NTP alone and NTP-C are compared under different reaction conditions, such as inlet reactant concentration, catalyst type, and energy density. AC exhibits the best benzene removal efficiency among three catalyst supports, and the performances of AO x /AC under different conditions follow the trend of CuO/AC > MnO/AC > MnO2/AC > Fe2O3/AC > AC > ZnO/AC > Ag2O/AC. The NTP with CuO/AC system exhibits the highest benzene elimination capability with almost 90.6 % inlet benzene removed at energy density of 70 and 270 J L−1. The strong adsorption ability of AC and the optimal catalytic ability of crystalline structure of CuO on the AC support may be contributed to the excellent performance of CuO/AC. It is found that the NO x by-product also can be well controlled over NTP-CuO/AC system. Additionally, the surface of CuO/AC is more slipperier and homogeneous with the reaction proceeding, indicating higher stability of CuO/AC.

Core-shell nanoparticle and method of generating an optical signal using the same

Abstract: A core-shell nanoparticle is provided. The core-shell nanoparticle has a core comprising a metal fluoride doped with a first sensitizer and a shell surrounding the core, wherein the shell comprises a first layer comprising the metal fluoride doped with a second sensitizer and a first activator, and a second layer comprising the metal fluoride doped with a third sensitizer and a second activator, wherein the first activator and the second activator are different, and each is independently selected from the group consisting of Tm 3+ , Ho 3+ , and combinations thereof. A method of generating an optical signal using the core-shell nanoparticle and a method of preparing the core-shell nanoparticle is also provided.