Mingyuan Gao

Electroluminescence of different colors from polycation/CdTe nanocrystal self-assembled films

Water soluble thiol capped CdTe nanocrystals are assembled into ultrathin films in combination with poly(diallyldimethylammonium chloride) (PDDA) by the self-assembly method of layer-by-layer adsorption of oppositely charged polyelectrolytes. Electroluminescent devices, which produce different color emissions, are fabricated by sandwiching CdTe/PDDA films between indium–tin–oxide (ITO) and aluminum electrodes using CdTe nanocrystals of different sizes. It is shown that the electroluminescence (EL) spectra of the CdTe/polymer films are nearly identical to the photoluminescence spectra of the corresponding CdTe nanocrystals in aqueous solutions. The devices produce room-light visible light output with an external quantum efficiency up to 0.1%. Light emission is observed at current densities of 10 mA/cm2 and at low onset voltages of 2.5–3.5 V, which depends on the thickness of the film indicating field-dependent current injection. A variation of the EL efficiency with the size of the CdTe particles is observ...

Receptor-mediated delivery of magnetic nanoparticles across the blood-brain barrier.

A brain delivery probe was prepared by covalently conjugating lactoferrin (Lf) to a poly(ethylene glycol) (PEG)-coated Fe(3)O(4) nanoparticle in order to facilitate the transport of the nanoparticles across the blood-brain barrier (BBB) by receptor-mediated transcytosis via the Lf receptor present on cerebral endothelial cells. The efficacy of the Fe(3)O(4)-Lf conjugate to cross the BBB was evaluated in vitro using a cell culture model for the blood-brain barrier as well as in vivo in SD rats. For an in vitro experiment, a well-established porcine BBB model was used based on the primary culture of cerebral capillary endothelial cells grown on filter supports, thus allowing one to follow the transfer of nanoparticles from the apical (blood) to the basolateral (brain) side. For in vivo experiments, SD rats were used as animal model to detect the passage of the nanoparticles through the BBB by MRI techniques. The results of both in vitro and in vivo experiments revealed that the Fe(3)O(4)-Lf probe exhibited an enhanced ability to cross the BBB in comparison to the PEG-coated Fe(3)O(4) nanoparticles and further suggested that the Lf-receptor-mediated transcytosis was an effective measure for delivering the nanoparticles across the BBB.

In vivo covalent cross-linking of photon-converted rare-earth nanostructures for tumour localization and theranostics

The development of precision nanomedicines to direct nanostructure-based reagents into tumour-targeted areas remains a critical challenge in clinics. Chemical reaction-mediated localization in response to tumour environmental perturbations offers promising opportunities for rational design of effective nano-theranostics. Here, we present a unique microenvironment-sensitive strategy for localization of peptide-premodified upconversion nanocrystals (UCNs) within tumour areas. Upon tumour-specific cathepsin protease reactions, the cleavage of peptides induces covalent cross-linking between the exposed cysteine and 2-cyanobenzothiazole on neighbouring particles, thus triggering the accumulation of UCNs into tumour site. Such enzyme-triggered cross-linking of UCNs leads to enhanced upconversion emission upon 808 nm laser irradiation, and in turn amplifies the singlet oxygen generation from the photosensitizers attached on UCNs. Importantly, this design enables remarkable tumour inhibition through either intratumoral UCNs injection or intravenous injection of nanoparticles modified with the targeting ligand. Our strategy may provide a multimodality solution for effective molecular sensing and site-specific tumour treatment.

Lateral flow immunochromatographic assay for sensitive pesticide detection by using Fe3O4 nanoparticle aggregates as color reagents.

Magnetic Fe(3)O(4) particle aggregates were prepared by cross-linking Fe(3)O(4) nanoparticles bearing surface carbonyl groups with poly-L-lysine. Upon further coupling with antiparaoxon methyl polyclonal antibody, the resultant particle aggregate-based probes were used in a lateral flow immunochromatographic assay (LFIA) of pesticide residue of paraoxon methyl. The results were compared with that achieved by using the mother Fe(3)O(4) nanoparticles. More quantitative results on the signal amplification effect endowed by the controlled aggregation of Fe(3)O(4) nanoparticles were extracted by relative optical density analysis. Under optimized conditions, a detection limit of 1.7 ng/mL for paraoxon methyl was achieved by using the particle aggregates, which is almost 40-fold lower than that based on the mother Fe(3)O(4) nanoparticles.

Facile synthesis of ultrasmall PEGylated iron oxide nanoparticles for dual-contrast T1- and T2-weighted magnetic resonance imaging

The development of new types of high-performance nanoparticulate MR contrast agents with either positive (T(1)) or dual-contrast (both positive and negative, T(1) + T(2)) ability is of great importance. Here we report a facile synthesis of ultrasmall PEGylated iron oxide nanoparticles for dual-contrast T(1)- and T(2)-weighted MRI. The produced superparamagnetic iron oxide nanoparticles (SPIONs) are of high crystallinity and size uniformity with an average diameter of 5.4 nm, and can be individually dispersed in the physiological buffer with high stability. The SPIONs reveal an impressive saturation magnetization of 94 emu g(-1) Fe(3)O(4), the highest r(1) of 19.7 mM(-1) s(-1) and the lowest r(2)/r(1) ratio of 2.0 at 1.5 T reported so far for PEGylated iron oxide nanoparticles. T(1)- and T(2)-weighted MR images showed that the SPIONs could not only improve surrounding water proton signals in the T(1)-weighted image, but induce significant signal reduction in the T(2)-weighted image. The good contrast effect of the SPIONs as T(1) + T(2) dual-contrast agents might be due to its high magnetization, optimal nanoparticle size for T(1) + T(2) dual-contrast agents, high size monodispersity and excellent colloidal stability. In vitro cell experiments showed that the SPIONs have little effect on HeLa cell viability.

Are rare-earth nanoparticles suitable for in vivo applications?

Rare earth (RE) nanoparticles have attracted considerable attention due to their unique optical and magnetic properties associated with f-electrons. The recent accomplishments in RE nanoparticle synthesis have aroused great interest of scientists to further explore their biomedical applications. This Research News summarizes recent achievements in controlled synthesis of magnetic and luminescent RE nanoparticles, surface modification, and toxicity studies of RE nanomaterials, and highlights state-of-the-art in in vivo applications of RE nanoparticles.

Aqueous Based Semiconductor Nanocrystals

This review summarizes traditional and recent nonconventional, bioinspired, methods for the aqueous synthesis of colloidal semiconductor quantum dots (QDs). The basic chemistry concepts are critically emphasized at the very beginning as these are strongly correlated with the selection of ligands and the optimal formation of aqueous QDs and their more sophisticated structures. The synergies of biomimetic and biosynthetic methods that can combine biospecific reactivity with the robust and strong optical responses of QDs have also resulted in new approaches to the synthesis of the nanoparticles themselves. A related new avenue is the recent extension of QD synthesis to form nanoparticles endowed with chiral optical properties. The optical characteristics of QD materials and their advanced forms such as core/shell heterostructures, alloys, and doped QDs are discussed: from the design considerations of optical band gap tuning, the control and reduction of the impact of surface traps, the consideration of charge carrier processes that affect emission and energy and charge transfer, to the impact and influence of lattice strain. We also describe the considerable progress in some selected QD applications such as in bioimaging and theranostics. The review concludes with future strategies and identification of key challenges that still need to be resolved in reaching very attractive, scalable, yet versatile aqueous syntheses that may widen the scope of commercial applications for semiconductor nanocrystals.

Magnetically Engineered Semiconductor Quantum Dots as Multimodal Imaging Probes

Light-emitting semiconductor quantum dots (QDs) combined with magnetic resonance imaging contrast agents within a single nanoparticle platform are considered to perform as multimodal imaging probes in biomedical research and related clinical applications. The principles of their rational design are outlined and contemporary synthetic strategies are reviewed (heterocrystalline growth; co-encapsulation or assembly of preformed QDs and magnetic nanoparticles; conjugation of magnetic chelates onto QDs; and doping of QDs with transition metal ions), identifying the strengths and weaknesses of different approaches. Some of the opportunities and benefits that arise through in vivo imaging using these dual-mode probes are highlighted where tumor location and delineation is demonstrated in both MRI and fluorescence modality. Work on the toxicological assessments of QD/magnetic nanoparticles is also reviewed, along with progress in reducing their toxicological side effects for eventual clinical use. The review concludes with an outlook for future biomedical imaging and the identification of key challenges in reaching clinical applications.

Polyaniline/Fe3O4 Nanoparticle Composite : Synthesis and Reaction Mechanism

Polyaniline/Fe(3)O(4) nanoparticle composite was prepared by polymerizing aniline in the presence of Fe(3)O(4) nanoparticles upon the use of H(2)O(2) as oxidant. The polymerization was monitored by ultraviolet-visible absorption spectroscopy. The microstructure of the resultant composite was characterized by transmission electron microscopy. The molecular structure of the resultant polyaniline in the composite was investigated by both Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, while the magnetic property of the composite was characterized by vibrating sample magnetometer. Furthermore, the microwave absorption property of the resultant composite was measured in a frequency range of 2-18 GHz. Systematic investigations revealed that carboxylic acid in the buffer presented a determined role in the polymerization of aniline. To discover the role of carboxylic acid in the polymerization of aniline, more control experiments were designed and carried out by theoretical calculation in combination with electron spin resonance measurements. It was for the first time found out that carboxylic acid such as acetic acid and succinic acid can not only catalyze the polymerization of aniline but also facilitate the generation of hydroxyl radical via the decomposition of H(2)O(2).

Magnetically engineered Cd-free quantum dots as dual-modality probes for fluorescence/magnetic resonance imaging of tumors.

Magnetically engineered Cd-free CuInS2@ZnS:Mn quantum dots (QDs) were designed, synthesized, and evaluated as potential dual-modality probes for fluorescence and magnetic resonance imaging (MRI) of tumors in vivo. The synthesis of Mn-doped core-shell structured CuInS2@ZnS mainly comprised three steps, i.e., the preparation of fluorescent CuInS2 seeds, the particle surface coating of ZnS, and the Mn-doping of the ZnS shells. Systematic spectroscopy studies were carried out to illustrate the impacts of ZnS coating and the following Mn-doping on the optical properties of the QDs. In combination with conventional fluorescence, fluorescence excitation, and time-resolved fluorescence measurements, the structure of CuInS2@ZnS:Mn QDs prepared under optimized conditions presented a Zn gradient CuInS2 core and a ZnS outer shell, while Mn ions were mainly located in the ZnS shell, which well balanced the optical and magnetic properties of the resultant QDs. For the following in vivo imaging experiments, the hydrophobic CuInS2@ZnS:Mn QDs were transferred into water upon ligand exchange reactions by replacing the 1-dodecanethiol ligand with dihydrolipoic acid-poly(ethylene glycol) (DHLA-PEG) ligand. The MTT assays based on HeLa cells were carried out to evaluate the cytotoxicity of the current Cd-free CuInS2@ZnS:Mn QDs for comparing with that of water soluble CdTe QDs. Further in vivo fluorescence and MR imaging experiments suggested that the PEGylated CuInS2@ZnS:Mn QDs could well target both subcutaneous and intraperitoneal tumors in vivo.