Yongquan Wu

A nonemissive iridium(III) complex that specifically lights-up the nuclei of living cells.

A nonemissive cyclometalated iridium(III) solvent complex, without conjugation with a cell-penetrating molecular transporter, [Ir(ppy)(2)(DMSO)(2)](+)PF(6)(-) (LIr1), has been developed as a first reaction-based fluorescence-turn-on agent for the nuclei of living cells. LIr1 can rapidly and selectively light-up the nuclei of living cells over fixed cells, giving rise to a significant luminescence enhancement (200-fold), and shows very low cytotoxicity at the imaging concentration (incubation time <10 min, LIr1 concentration 10 μM). More importantly, in contrast to the reported nuclear stains that are based on luminescence enhancement through interaction with nucleic acids, complex LIr1 as a nuclear stain has a reaction-based mode of action, which relies on its rapid reaction with histidine/histidine-containing proteins. Cellular uptake of LIr1 has been investigated in detail under different conditions, such as at various temperatures, with hypertonic treatment, and in the presence of metabolic and endocytic inhibitors. The results have indicated that LIr1 permeates the outer and nuclear membranes of living cells through an energy-dependent entry pathway within a few minutes. As determined by an inductively coupled plasma atomic emission spectroscopy (ICP-AEC), LIr1 is accumulated in the nuclei of living cells and converted into an intensely emissive adduct. Such novel reaction-based nuclear staining for visualizing exclusively the nuclei of living cells with a significant luminescence enhancement may extend the arsenal of currently available fluorescent stains for specific staining of cellular compartments.

Hydrothermal synthesis of NaLuF4:153Sm,Yb,Tm nanoparticles and their application in dual-modality upconversion luminescence and SPECT bioimaging.

Upconversion luminescence (UCL) properties and radioactivity have been integrated into NaLuF(4):(153)Sm,Yb,Tm nanoparticles by a facile one-step hydrothermal method, making these nanoparticles potential candidates for UCL and single-photon emission computed tomography (SPECT) dual-modal bioimaging inxa0vivo. The introduction of small amount of radioactive (153)Sm(3+) can hardly vary the upconversion luminescence properties of the nanoparticles. The as-designed nanoparticles showed very low cytotoxicity, no obvious tissue damage in 7 days, and excellent inxa0vitro and inxa0vivo performances in dual-modal bioimaging. By means of a combination of UCL and SPECT imaging inxa0vivo, the distribution of the nanoparticles in living animals has been studied, and the results indicated that these particles were mainly accumulated in the liver and spleen. Therefore, the concept of (153)Sm(3+)/Yb(3+)/Tm(3+) co-doped NaLuF(4) nanoparticles for UCL and SPECT dual-modality imaging inxa0vivo of whole-body animals may serve as a platform for next-generation probes for ultra-sensitive molecular imaging from the cellular scale to whole-body evaluation. It also introduces an easy methodology to quantify inxa0vivo biodistribution of nanomaterials which still needs further understanding as a community.

Polyphosphoric acid capping radioactive/upconverting NaLuF4:Yb,Tm,153Sm nanoparticles for blood pool imaging in vivo

Nanoparticles that circulate in the bloodstream for a prolonged period of time have important biomedicine applications. However, no example of lanthanide-based nanoparticles having a long-term circulation bloodstream has been reported to date. Herein, we report on difunctional radioactive and upconversion nanoparticles (UCNP) coated with polyphosphoric acid ligand, that is ethylenediamine tetramethylenephosphonic acid (EDTMP), for an application in single-photon emission computed tomography (SPECT) blood pool imaging. The structure, size and zeta-potential of the EDTMP-coated nanoparticles (EDTMP-UCNP) are verified using transmission electron microscopy and dynamic light scattering. Injection of radioisotope samarium-153-labeled EDTMP-UCNP (EDTMP-UCNP:(153)Sm) into mice reveal superior circulation time compared to control nanoparticles coated with citric acid (cit-UCNP:(153)Sm) and (153)Sm complex of EDTMP (EDTMP-(153)Sm). The mechanism for the extended circulation time may be attributed to the adhesion of EDTMP-UCNP on the membrane of red blood cells (RBCs). In vivo toxicity results show no toxicity of EDTMP-UCNP at the dose of 100 mg/kg, validating its safety as an agent for blood pool imaging. Our results provide a new strategy of nanoprobe for a long-term circulation bloodstream by introducing polyphosphoric acid as surface ligand.

Biodistribution of sub-10 nm PEG-modified radioactive/upconversion nanoparticles

The biodistribution of lanthanide-based upconversion nanophosphors (UCNPs) has attracted increasing attention, and all of the reported UCNPs display metabolism in the liver and spleen mainly. Herein, ∼8xa0nm poly(ethylene glycol) (PEG)-coated NaYF4 nanoparticles codoped with Yb(3+), Er(3+), and (or) radioactive (153)Sm(3+) ions were synthesized, through a hydrothermal synthetic system assisted by binary cooperative ligands with oleic acid and PEG dicarboxylic acids. The as-prepared PEG-coating NaYF4:Yb,Er and NaYF4:Yb,Er,(153)Sm are denoted as PEG-UCNPs and PEG-UCNPs((153)Sm), respectively. PEG-UCNPs were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD) analysis, and Fourier-transform infrared (FTIR) spectroscopy. The PEG-UCNPs showed excellent water solubility with a hydrodynamic diameter of ∼10xa0nm and displayed upconversion luminescence (UCL) under continuous-wave excitation at 980xa0nm. At the same time, the (153)Sm-doped nanoparticles PEG-UCNPs((153)Sm) displayed radioactivity, and time-dependent biodistribution of PEG-UCNPs((153)Sm) was investigated, through single-photon emission computed tomography (SPECT) imaging and γ-counter analysis. Interestingly, PEG-UCNPs((153)Sm) had a long blood retention time and were partly eliminated through urinary pathways inxa0vivo. Therefore, the concept of fabricating PEG-coated, small nanosize (sub-10xa0nm) nanoparticles with radioactive property is a useful strategy for providing a potential method to monitor lanthanide nanoparticles renal clearable.

A water-soluble phosphorescent polymer for time-resolved assay and bioimaging of cysteine/homocysteine

A water-soluble phosphorescent bioprobe was successfully developed by introducing an iridium(iii) complex as a phosphorescent signaling unit with poly(N-isopropylacrylamide) (PNIPAM) as the stimuli-responsive backbone. The probe was used for the effective detection of cysteine (Cys)/homocysteine (Hcy) and temperature based on changes in the phosphorescence signal. The design principle was based on the fact that the aldehyde groups in the cyclometalated ligands of the iridium(iii) complex moiety can react with the β- or γ-aminothiol group to form thiazolidine or thiazinane, respectively, resulting in a phosphorescence change in the iridium(iii) complex, thereby facilitating the detection of Cys and Hcy. Moreover, a phosphorescent hydrogel based on this probe was formed upon cross-linking and was then used as a quasi-solid sensing system for detecting Cys and Hcy. Furthermore, by using a time-resolved photoluminescence technique, the probe can detect Hcy in the presence of intense background fluorescence. In addition, phase changes in temperature-responsive PNIPAM can result in a switch of microenvironment between hydrophilicity and hydrophobicity, to which the phosphorescent emission of the iridium(iii) complex is very sensitive. This bioprobe integrates water solubility, biocompatibility, and sensing capability into one system, which is advantageous for biological applications. Further investigation of the application of the bioprobe for living-cell imaging confirmed that the probe is membrane permeable and is capable of detecting Cys in living cells with notable phosphorescence enhancement. Fluorescence lifetime imaging microscopy is successfully applied for sensing and bioimaging of intracellular Cys in the presence of short-lived background fluorescence.

Iridium complex triggered white-light-emitting gel and its response to cysteine

Phenol substituted 1,8-naphthalimide derivatives acting as a donor and an iridium(III) complex which emits orange light acting as an acceptor were synthesized to fabricate a novel white-light-emitting two-component gel. The intermolecular energy transfer between the two components plays a crucial role in providing the tuneable emission in the mixed gels. The emission of white light can be obtained by carefully tuning the ratio of the two components. These gels are ideal constituents for the design of supramolecular light-harvesting materials, which afford a novel approach to displaying information in soft materials with tuneable optical properties. Furthermore, the two-component gel can respond to cysteine with an obvious change in luminescence that is visible to the naked eye.

Long-term in vivo biodistribution and toxicity of Gd(OH)3 nanorods.

The long-term retention of nanomaterials in the body is one of the biggest concerns about the safety of these materials for in vivo application. So, it is important to develop some nanomaterials which can be relatively more easily excreted. Rare earth hydroxide, that can be degraded under acidic condition in vivo, is one of the suitable candidates. Herein, Gd(OH)(3) nanorods, which are considered as magnetic resonance imaging (MRI) contrast agents, have been synthesized to evaluate their excretion process and potential toxicity. The long-term in vivo biodistribution of the materials was investigated using single photon emission computed tomography (SPECT) imaging with (153)Sm-doped Gd(OH)(3) nanorods as probes. Biodistribution results showed that the uptake and retention of the Gd(OH)(3) nanorods took place primarily in the liver, spleen and lung. Then, most of the nanorods were excreted from the bodies of mice very rapidly. Body weight data for the mice indicated that, when intravenously injected with 100 mg/kg of the nanorods, the mice survived for 150 days without any apparent adverse effects to their health. In addition, histological, hematological and biochemical analysis indicated that these nanorods have no overt toxicity.

The cellular uptake and localization of non-emissive iridium(III) complexes as cellular reaction-based luminescence probes

Improvement of cellular uptake and subcellular resolution remains a major obstacle in the successful and broad application of cellular optical probes. In this context, we design and synthesize seven non-emissive cyclometalated iridium(III) solvent complexes [Ir(CˆN)(2)(solv)(2)](+)L(-) (LIr2-LIr8, in which CˆN = 2-phenylpyridine (ppy) or its derivative; solv = DMSO, H(2)O or CH(3)CN; L(-) = PF(6)(-) or OTf(-)) applicable in live cell imaging to facilitate selective visualization of cellular structures. Based on the above variations (including different counter ions, solvent ligands, and CˆN ligands), structure-activity relationship analyses reveal a number of clear correlations: (1) variations in counter anions and solvent ligands of iridium(III) complexes do not affect cellular imaging behavior, and (2) length of the side carbon chain in CˆN ligands has significant effects on cellular uptake and localization/accumulation of iridium complexes in living cells. Moreover, investigation of the uptake mechanism via low-temperature and metabolism inhibitor assays reveal that [Ir(4-Meppy)(2)(CH(3)CN)(2)](+)OTf(-) (LIr5) with 2-phenylpyridine derivative with side-chain of methyl group at the 4-position as CˆN ligand permeates the outer and nuclear membranes of living cells through an energy-dependent, non-endocytic entry pathway, and translocation of the complex from the cell periphery towards the perinuclear region possibly occurs through a microtubule-dependent transport pathway. Nuclear pore complexes (NPCs) appear to selectively control the transport of iridium(III) complexes between the cytoplasm and nucleus. A generalization of trends in behavior and structure-activity relationships is presented, which should provide further insights into the design and optimization of future probes.

Visible-light-excited and europium-emissive nanoparticles for highly-luminescent bioimaging in vivo.

Europium(III)-based material showing special milliseconds photoluminescence lifetime has been considered as an ideal time-gated luminescence probe for bioimaging, but is still limited in application in luminescent small-animal bioimaging inxa0vivo. Here, a water-soluble, stable, highly-luminescent nanosystem, Ir-Eu-MSN (MSNxa0=xa0mesoporous silica nanoparticles, Ir-Euxa0=xa0[Ir(dfppy)2(pic-OH)]3Eu·2H2O, dfppyxa0=xa02-(2,4-difluorophenyl)pyridine, pic-OHxa0=xa03-hydroxy-2-carboxypyridine), was developed by an in situ coordination reaction to form an insoluble dinuclear iridium(III) complex-sensitized-europium(III) emissive complex within mesoporous silica nanoparticles (MSNs) which had high loading efficiency. Compared with the usual approach of physical adsorption, this in-situ reaction strategy provided 20-fold the loading efficiency (43.2%) of the insoluble Ir-Eu complex in MSNs. These nanoparticles in solid state showed bright red luminescence with high quantum yield of 55.2%, and the excitation window extended up to 470xa0nm. These Ir-Eu-MSN nanoparticles were used for luminescence imaging in living cells under excitation at 458xa0nm with confocal microscopy, which was confirmed by flow cytometry. Furthermore, the Ir-Eu-MSN nanoparticles were successfully applied into high-contrast luminescent lymphatic imaging inxa0vivo under low power density excitation of 5xa0mWxa0cm(-2). This synthetic method provides a universal strategy of combining hydrophobic complexes with hydrophilic MSNs for inxa0vivo bioimaging.

Phosphorescent platinum(II) complexes containing different β-diketonate ligands: synthesis, tunable excited-state properties, and their application in bioimaging

A series of square-planar Pt(II) complexes [Pt(C^N)(O^O)] (1–5) (C^N = 2-phenylpyridine, O^O denotes a series of β-diketonate ligands) is reported. Detailed studies of theoretical calculations, electrochemical and photophysical properties have shown that their excited states can be attributed to the mixing of 3MLCT, 3LLCT and 3LC/3ILCT transitions. For 1, the excited state is dominated by the C^N ligand. The excited states of complexes 2–5, however, are dominated by O^O ligands. Through variation of the β-diketonate ligands, the emission colors of 1–5 can be tuned from blue-green to yellow. Further investigations have revealed that the emission of 4 in the solid state can be attributed to the 3MLCT and 3LLLCT transitions, which has been confirmed by X-ray diffraction studies as well as theoretical calculations. Moreover, exclusive staining of cytoplasm and low cytotoxicity have been observed for 1–4, which makes them promising candidates as phosphorescent probes for bioimaging.