Huan-Ming Xiong

Full-Color Light-Emitting Carbon Dots with a Surface-State-Controlled Luminescence Mechanism

Carbon dots (CDs) with tunable photoluminescence (PL) and a quantum yield of up to 35% in water were hydrothermally synthesized in one pot and separated via silica column chromatography. These separated CDs emitted bright and stable luminescence in gradient colors from blue to red under a single-wavelength UV light. They exhibited high optical uniformity; that is, every sample showed only one peak in the PL excitation spectrum, only one peak in the excitation-independent PL emission spectrum, and similar monoexponential fluorescence lifetimes. Although these samples had similar distributions of particle size and graphite structure in their carbon cores, the surface state gradually varied among the samples, especially the degree of oxidation. Therefore, the observed red shift in their emission peaks from 440 to 625 nm was ascribed to a gradual reduction in their band gaps with the increasing incorporation of oxygen species into their surface structures. These energy bands were found to depend on the surface groups and structures but not on the particle size, not as in traditional semiconductor quantum dots. In addition, because of their excellent PL properties and low cytotoxicity, these CDs could be used to image cells in different colors under a single-wavelength light source, and the red-emitting CDs could be used to image live mice because of the strong penetration capability of their fluorescence.

Stable Aqueous ZnO@Polymer Core−Shell Nanoparticles with Tunable Photoluminescence and Their Application in Cell Imaging

Stable aqueous solutions of ZnO@polymer core-shell nanoparticles with tunable photoluminescence are prepared through a simple sol-gel route. The copolymer shell has many hydrophilic external groups and a hydrophobic internal layer which connects ZnO cores through covalent bonds. The optimal samples show quantum yield above 50% and stable emission for months. These samples with their concentrations of below 0.2 mg/mL are nontoxic to human cells. After uptake of these ZnO@polymer nanoparticles, the luminescent cells have enough life under UV light for microscopic imaging.

Carbon-Coated Li4Ti5O12 as a High Rate Electrode Material for Li-Ion Intercalation

Li 4 Ti 5 O 12 is a promising electrode material for high power density lithium-ion batteries and hybrid supercapacitors, but has the drawback of low electrical conductivity. We report a thermal vapor decomposition method to coat a uniform nanothickness graphitized-carbon on the Li 4 Ti 5 O 12 particle surface. The resulting product coated at 800°C has a 5 nm thick carbon layer and a electrical conductivity of 2.05 S/cm, which is much higher than that of raw Li 4 Ti 5 O 12 (<10 -13 S/cm). As a result, it shows much better rate capability when used as a negative electrode for electrochemical supercapacitors. AC impedance measurements reveal that the carbon-coated Li 4 Ti 5 O 12 has smaller charge-transfer resistance due to large effective interface reaction area.

ZnO Nanoparticles Applied to Bioimaging and Drug Delivery

The last decade has seen significant achievements in biomedical diagnosis and therapy at the levels of cells and molecules. Nanoparticles with luminescent or magnetic properties are used as detection probes and drug carriers, both in vitro and in vivo. ZnO nanoparticles, due to their good biocompatibility and low cost, have shown promising potential in bioimaging and drug delivery. The recent exciting progress on the biomedical applications of ZnO-based nanomaterials is reviewed here, along with discussions on the advantages and limitations of these advanced materials and suggestions for improving methods.

Sonochemical Synthesis of Highly Luminescent Zinc Oxide Nanoparticles Doped with Magnesium(II)

A bright idea: Mg/ZnO nanoparticles that exhibit bright, stable photoluminescence both in colloidal dispersions and in the solid state are formed by doping Mg(II) ions into ZnO nanoparticles by sonochemical synthesis. The changes in their band gaps and luminescence properties rely on the defect concentrations inside the ZnO nanoparticles; these concentrations are determined by the Mg/Zn molar ratios (see picture).

Nanosized Li4Ti5O12 Prepared by Molten Salt Method as an Electrode Material for Hybrid Electrochemical Supercapacitors

Nanosized lithium titanium oxide (Li 4 Ti 5 O 12 ) powder has been prepared using LiCl as a high-temperature flux. X-ray diffraction, scanning electron microscope, and transmission electron microscope measurements indicate that the obtained Li 4 Ti 5 O 12 particles are uniform and the particle size of Li 4 Ti 5 O 12 powder can be controlled by flux content and heating time. Under the optimal synthetic condition, the particle-size distribution is narrow (∼100 nm). The hybrid electrochemical supercapacitors using a nanosized Li 4 Ti 5 O 12 negative electrode in combination with an activated carbon positive electrode show much better rate capability than those based on the conventional Li 4 Ti 5 O 12 prepared by solid-state reaction.

Photoluminescent ZnO nanoparticles modified by polymers

Photoluminescent ZnO nanoparticles, due to nontoxicity and cheapness, are promising materials applied in UV laser devices and biological labels. ZnO photoluminescence is usually composed of two parts: UV emission arising from the typical band gap transition and visible emission due to the oxygen vacancies. In order to protect ZnO nanoparticles and improve their optical properties, polymers are mixed with ZnO or modified on ZnO surfaces to produce various nanocomposites. In the meantime, some new luminescent phenomena are found when polymers and ZnO nanoparticles together participate in the luminescent process. This review will focus on the synthetic methods, structural features and photoluminescent properties of the polymer–ZnO nanocomposites.

Luminescent carbon quantum dots and their application in cell imaging

A facile hydrothermal method was used to synthesize luminescent carbon dots from single-walled carbon nanotubes (SWNTs). Then 4,7,10-trioxa-1,13-tridecanediamine (TTDDA) was grafted onto the carbon dots to increase their water solubility and luminescent properties. The as-prepared carbon dots were characterized by UV-Vis absorption, infrared (IR), Raman, fluorescence, and transmission electron microscopy (TEM). The results confirmed that these carbon dots were monodispersed in water and emitted bright yellow fluorescence. The surface modified carbon dots were used to label biological cells, and the images obtained by a laser scanning confocal microscope showed that the carbon dots were gradually taken up by HeLa cells. The cytotoxicity of such carbon dots toward HeLa cells was very low, for 24 h the LC50 was over 5 mg mL−1.

One-pot synthesis of water-dispersible Ag2S quantum dots with bright fluorescent emission in the second near-infrared window

The second near-infrared window (NIR-II, wavelength of 1.0-1.4 μm) is optimal for the bioimaging of live animals due to their low albedo and endogenous autofluorescence. Herein, we report a facile and one-pot biomimetic synthesis approach to prepare water-dispersible NIR-II-emitting ultrasmall Ag(2)S quantum dots (QDs). Photoluminescence spectra showed that the emission peaks could be tuned from 1294 to 1050 nm as the size of the Ag(2)S QDs varied from 6.8 to 1.6 nm. The x-ray diffraction patterns and x-ray photoelectron spectra confirmed that the products were monoclinic α-Ag(2)S. Fourier transform infrared spectrograph analysis indicated that the products were protein-conjugated Ag(2)S QDs. Examination of cytotoxicity and the hemolysis test showed that the obtained Ag(2)S QDs had good biocompatibility, indicating that such a nanomaterial could be a new kind of fluorescent label for in vivo imaging.

ZnO-poly(methyl methacrylate) nanobeads for enriching and desalting low-abundant proteins followed by directly MALDI-TOF MS analysis

A fast solid-phase microextraction method using core-shell ZnO-poly (methyl methacrylate) nanobeads (ZnO-PMMA) as adsorbent was established. This fast method with high enriching efficiency and salt tolerance capability depends on the structure of the core-shell nanobeads. First, the large surface area of the PMMA shell makes the dispersive nanobeads capture samples quickly, by virtue of multi-interactions between ZnO-PMMA and samples except for the interaction with salts. Second, the small nanosize of the ZnO-core (2.1 nm) and the flexible hydrophobic PMMA shell, which can prevent the cores from aggregation, make the nanobeads form a homogeneous layer on the matrix-assisted laser desorption/ionization (MALDI) plate and do not hinder the cocrystallization of the matrix and samples. Third, the ZnO core also prevents PMMA from fragmentation and ionization in mass spectrometer. In this article, approximately 80% bovine serum albumin digests were enriched by ZnO-PMMA from 100 amol/muL solution within 10-min incubation, and the solid phase can be directly analyzed by MALDI mass spectrometry. Mass intensity can be increased 5-10-fold (ZnO-PMMA enrichment vs lyophilization). High-quality mass spectra can be obtained, even with the presence of saturated NaCl (6.2 M), saturated NH 4HCO 3 (2.6 M), or 1 M urea. This method has been successfully applied to human colorectal cancer proteome research, and eight new proteins have been found.