Showing papers by "Shuit-Tong Lee published in 2011"

In Vivo Pharmacokinetics, Long-Term Biodistribution, and Toxicology of PEGylated Graphene in Mice

Abstract: Graphene has emerged as interesting nanomaterials with promising applications in a range of fields including biomedicine. In this work, for the first time we study the long-term in vivo biodistribution of 125I-labeled nanographene sheets (NGS) functionalized with polyethylene glycol (PEG) and systematically examine the potential toxicity of graphene over time. Our results show that PEGylated NGS mainly accumulate in the reticuloendothelial system (RES) including liver and spleen after intravenous administration and can be gradually cleared, likely by both renal and fecal excretion. PEGylated NGS do not cause appreciable toxicity at our tested dose (20 mg/kg) to the treated mice in a period of 3 months as evidenced by blood biochemistry, hematological analysis, and histological examinations. Our work greatly encourages further studies of graphene for biomedical applications.

Silicon Nanowires for Photovoltaic Solar Energy Conversion

Abstract: Semiconductor nanowires are attracting intense interest as a promising material for solar energy conversion for the new-generation photovoltaic (PV) technology. In particular, silicon nanowires (SiNWs) are under active investigation for PV applications because they offer novel approaches for solar-to-electric energy conversion leading to high-efficiency devices via simple manufacturing. This article reviews the recent developments in the utilization of SiNWs for PV applications, the relationship between SiNW-based PV device structure and performance, and the challenges to obtaining high-performance cost-effective solar cells.

Fe2O3/carbon quantum dots complex photocatalysts and their enhanced photocatalytic activity under visible light

Abstract: In this study, we report the facile fabrication of Fe2O3/CQDs nanocomposites, and investigate their effective photocatalytic activity for the photodegradation of toxic gas (gas-phase benzene and methanol) under visible light. The crucial roles of CQDs in the enhancement of photocatalytic activity of the Fe2O3/CQDs composites are illustrated.

Hybrid heterojunction solar cell based on organic-inorganic silicon nanowire array architecture.

Abstract: Silicon nanowire arrays (SiNWs) on a planar silicon wafer can be fabricated by a simple metal-assisted wet chemical etching method. They can offer an excellent light harvesting capability through light scattering and trapping. In this work, we demonstrated that the organic–inorganic solar cell based on hybrid composites of conjugated molecules and SiNWs on a planar substrate yielded an excellent power conversion efficiency (PCE) of 9.70%. The high efficiency was ascribed to two aspects: one was the improvement of the light absorption by SiNWs structure on the planar components; the other was the enhancement of charge extraction efficiency, resulting from the novel top contact by forming a thin organic layer shell around the individual silicon nanowire. On the contrary, the sole planar junction solar cell only exhibited a PCE of 6.01%, due to the lower light trapping capability and the less hole extraction efficiency. It indicated that both the SiNWs structure and the thin organic layer top contact were cr...

One-Pot Microwave Synthesis of Water-Dispersible, Ultraphoto- and pH-Stable, and Highly Fluorescent Silicon Quantum Dots

Abstract: Fluorescent silicon quantum dots (SiQDs) are facilely prepared via one-pot microwave-assisted synthesis. The as-prepared SiQDs feature excellent aqueous dispersibility, robust photo- and pH-stability, strong fluorescence, and favorable biocompatibility. Experiments show the SiQDs are superbly suitable for long-term immunofluorescent cellular imaging. Our results provide a new and invaluable methodology for large-scale synthesis of high-quality SiQDs, which are promising for various optoelectronic and biological applications.

Multicolor In Vivo Imaging of Upconversion Nanoparticles with Emissions Tuned by Luminescence Resonance Energy Transfer

Abstract: Upconversion nanoparticles (UCNPs) based on sodium yttrium fluoride (NaYF4) nanocrystals are synthesized, functionalized with an amphiphilic polymer, and loaded with fluorescent and quenching molecules by physical adsorption. The formed supramolecular UCNP−dye complexes show tuned visible emission spectra owing to the luminescence resonance energy transfer (LRET) from nanoparticles to the organic dyes under near-infrared (NIR) excitation, and can be well separated in multicolor imaging after spectral decovolution. Our work provides a facile and flexible method to modulate the upconversion luminescence (UCL) spectra of UCNPs for in vivo multicolor UCL imaging in animals.

Air Stable, Efficient Hybrid Photovoltaic Devices Based on Poly(3-hexylthiophene) and Silicon Nanostructures

Abstract: Efficient, stable hybrid photovoltaic (PV) devices based on poly(3-hexylthiophene) (P3HT) and silicon nanowire arrays (SiNWs) are reported A two-step, chlorination/methylation procedure is used to convert Si−H bonds into Si−C ones to reduce the velocity of charge recombination at the silicon surface as well as achieve a favorable alignment of band-edge energies In addition, Pt nanodots (PtNDs) are deposited onto the surface of the SiNWs to further tune the band-edge alignment and passivate nonmethylated silicon sites Methylated silicon surfaces modified with PtNDs possess a favorable internal electric field in accord with expectations based on the electron affinity (∼37 eV) and net positive surface dipole measured on such surfaces by ultraviolet photoemission spectroscopy This attests to the degree of chemical control that can be exerted over the internal electric field in such systems by surface functionalization In concert with methyl termination and decoration with PtNDs, hybrid PV devices based

Fluorescent carbon nanoparticles: electrochemical synthesis and their pH sensitive photoluminescence properties

Abstract: Highly fluorescent carbon nanoparticles were synthesized directly from ethanol by a one-step sodium hydroxide-assisted electrochemical treatment. These nanoparticles could emit bright and colorful photoluminescence covering the entire visible spectral range and had excellent up-conversion fluorescent, stable ionic, long fluorescence lifetime and pH-sensitive photoluminescence properties.

Single-walled carbon nanotubes in biomedical imaging

Abstract: This article reviews the latest developments in using single-walled carbon nanotubes (SWNTs) for biomedical imaging. SWNTs with a number of unique intrinsic optical properties have been widely used as contrast agents in Raman imaging, near-infrared (NIR) fluorescence imaging and photoacoustic imaging in vitro and in vivo. More imaging functionalities including positron emission tomography (PET) and magnetic resonance (MR) imaging can be achieved by either utilizing external labels or the metal impurities of nanotube samples. Although there is still a long way to go before SWNTs are ready for clinical use, they are promising nanomaterials with great potential in multimodality biomedical imaging.

High-performance silicon nanowire array photoelectrochemical solar cells through surface passivation and modification.

Abstract: Nanowire solar cells: Pt nanoparticle (PtNP) decorated C/Si core/shell nanowire photoelectrochemical solar cells show high conversion efficiency of 10.86 % and excellent stability in aggressive electrolytes under 1-sun AM 1.5 G illumination. Superior device performance is achieved by improved surface passivation of the nanowires by carbon coating and enhanced interfacial charge transfer by PtNPs.

Highly Reproducible Surface‐Enhanced Raman Scattering on a Capillarity‐Assisted Gold Nanoparticle Assembly

Abstract: A facile method based on capillarity-assisted assembly is used to fabricate high-performance surface-enhanced Raman scattering (SERS) substrates employing clean Au nanoparticles (NPs). This method is better than microchannel way because the former may supply large-area uniform assembly and overcome the uneven radial distribution. Such densely-arranged assembly of Au NPs exhibits high reproducibility and large Raman enhancement factors of 3 × 10 10 , arising from strong electromagnetic fi eld coupling induced by adjacent Au NPs. The spot-to-spot SERS signals show that the relative standard deviation (RSD) in the intensity of the main Raman vibration modes (1310, 1361, 1509, 1650 cm − 1 ) of Rhodamine 6G at a concentration of 1 × 10 − 10 M are consistently less than 20%, demonstrating good spatial uniformity and reproducibility. The SERS signals of sudan dye at a 1 × 10 − 8 M concentration also shows high reproducibility with a low RSD of < 20%. Further, the assembly substrate is stable, retaining excellent uniformity and sensitivity after storage for months. This assembly strategy integrating the advantages of low-cost production, high sensitivity, and reproducibility would signifi cantly facilitate practical SERS detection.

Water‐Dispersed Near‐Infrared‐Emitting Quantum Dots of Ultrasmall Sizes for In Vitro and In Vivo Imaging

Abstract: Near-infrared (NIR)-fluorescence imaging is widely recognized as an effective method for high-resolution and highsensitivity bioimaging because of its minimized biological autofluorescence background and the increased penetration of excitation and emission light through tissues in the NIR wavelength window (700–900 nm). There have been tremendous efforts to develop high-efficiency fluorescent biological probes for NIR-fluorescence imaging. Semiconductor quantum dots (QDs) have attracted much recent attention as a new generation of fluorescent probes because of their unique optical properties such as strong luminescence, high photostability, and size-tunable emission wavelength. While QDs emitting in the range of 450–650 nm have been well developed, NIR-emitting QDs have been much less explored because of their relatively complicated synthesis and post-treatment manipulations. Furthermore, NIR-emitting QDs are usually prepared in organic phase, and additional surface modification is employed to render them waterdispersible for biological applications. The relatively complicated surface modification often results in an increase in size of the QDs. Only recently, water-dispersed NIRemitting CdTe/CdS QDs with tetrahedral structure were directly prepared in aqueous phase through the epitaxialshell-growth method. Despite these advances, much work is still needed to obtain NIR-emitting QDs that can be facilely synthesized in aqueous phase for high-sensitivity and specific bioimaging. Herein, we report the first example of ultrasmall-sized NIR-emitting CdTe QDs with excellent aqueous dispersibility, robust storage, chemical, and photostability, and strong photoluminescence (photoluminescent quantum yield (PLQY): 15–20%). Significantly, the NIR QDs are directly synthesized in aqueous phase through a facile one-step microwave-assisted method (see the Supporting Information for experimental details and mechanisms) by utilizing several attractive properties of microwave irradiation such as prompt startup, easy heat control (on and off), prompt and homogeneous heating, and so forth. More importantly, highly spectrally and spatially resolved bioimaging was possible, and efficient tumor passive targeting in live mice was shown by using the prepared QDs. QDs with different emission wavelengths in the NIR range (lmax= 700–800 nm) can be readily prepared through fine adjustment of the experimental conditions (e.g., reaction time and temperature). Figure 1a,b displays the normalized ultraviolet photoluminescence (UV-PL) spectra for a series of as-prepared QDs with controllable maximum emission wavelength ranging from 700 to 800 nm in aqueous solution. Such QD solutions are transparent under ambient light conditions, suggesting the as-prepared QDs are well-dispersed in aqueous phase without further treatment (Figure 1c). The excellent aqueous dispersibility of the QDs arises from the surfacecovering mercaptopropionic acid (MPA) that acts as a stabilizer because of the presence of negatively charged carboxylic groups. Under UV irradiation the fluorescence of the as-prepared QDs became darker and the emission wavelength gradually shifted out of the visible region (Figure 1d). The transmission electron microscopy (TEM) and highresolution TEM (HRTEM) images reveal that the NIRemitting QDs are spherical particles with good monodispersibility (Figure 2a,b). The existence of a well-resolved crystal lattice in the HRTEM image further confirms the highly crystalline structures of the QDs (Figure 2b inset). Furthermore, the size distribution histogram (Figure 2c), which was determined by measuring more than 250 particles, shows that the average size and standard deviation of the as-prepared NIR-emitting QDs is (3.74 0.67) nm. Comparatively, the [*] Prof. Y. He, Y. L. Zhong, Dr. Y. Y. Su, Y. M. Lu, Z. Y. Jiang, F. Peng, T. T. Xu, Dr. S. Su Institute of Functional Nano & Soft Materials (FUNSOM) and Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University Suzhou, Jiangsu 215123 (China) Fax: (+86)512-6588-2846 E-mail: yaohe@suda.edu.cn

Small-sized silicon nanoparticles: new nanolights and nanocatalysts

Abstract: Owing to their abundant unique properties and ready compatibility with Si microelectronic technology, Si nanostructures are becoming one of the most important classes of nano semiconductors. Particularly, small-sized Si nanoparticles possess distinctive photoluminescence (PL), biocompatibility, and active surface properties. In this review, we focus on the synthesis and PL properties of small-sized Si nanoparticles and their potential applications in the fields of bioimaging and nanocatalysis. We further highlight major challenges and promises in this area.

Solvent-free ionic liquid/poly(ionic liquid) electrolytes for quasi-solid-state dye-sensitized solar cells

Abstract: Photochemically stable poly(ionic liquids) (poly(ILs)) including poly(1-butyl-3-vinylimidazolium bromide) ([PBVIm][Br]) and poly(1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide) ([PBVIm][TFSI]) were synthesized and dissolved in the room temperature ionic liquids (ILs) to form quasi-solid-state electrolytes for dye-sensitized solar cells (DSSCs), without using any volatile organic solvent. DSSCs based on IL/[PBVIm][TFSI] gel electrolyte yielded a power conversion efficiency of 4.4% under a simulated air mass 1.5 solar spectrum illumination at 100 mW cm−2. The superior long-term stability of fabricated DSSCs indicated that the DSSCs based on solvent-free IL/poly(ILs) gel electrolytes could overcome the drawbacks of cells containing volatile solvents.

Synthesis and characterization of phenanthroimidazole derivatives for applications in organic electroluminescent devices

Abstract: A series of phenanthroimidazole derivatives have been synthesized, characterized and applied as non-doped emitters in organic light-emitting devices. The compounds show high fluorescent quantum yields up to 0.75 as well as good thermal and film-forming abilities. Crystal structures of the compounds were determined by X-ray crystallography. Correlations between optoelectronic properties, energy levels and molecular structures of the materials were investigated. It was found that introduction of a thiophene ring on the C2-position of phenanthroimidazole can effectively decrease the ionization potentials (Ip) of the compounds. Fluorescent properties of the materials were found to be related to the dihedral angles in the compounds with different substituents. The low Ip (from 5.00 to 5.21 eV) of the materials enables efficient hole-injection from the hole-transporting layer and results in low turn-on (<2.7 V) and operation voltages (<5.5 V to give 1000 cd m−2).

Single-crystalline ZnTe nanowires for application as high-performance green/ultraviolet photodetector.

Abstract: Single-crystalline ZnTe nanowires were prepared by a simple vapor transport and deposition method. Photodetectors of individual ZnTe nanowires were fabricated to study photoconductivity of the nanowires. It was observed the nanowire photodetectors show the highest visible-light photoconductive gains among all reported photodetectors based on 1D nanostructure semiconductors, including CdS, CdSe, ZnSe, etc. The high photosensitivity and relatively fast response speed are attributable to the high crystal quality of the ZnTe nanowires. These results reveal that such single-crystalline ZnTe nanowires are excellent candidates for optoelectronic applications.

Distinct electroluminescent properties of triphenylamine derivatives in blue organic light-emitting devices

Abstract: Two highly fluorescent triphenylamines (TPA) end-capped respectively with one and three pyrene arms, namely N,N-diphenyl-4-(pyren-1-yl)aniline (PyTPA) and 4,4′,4′′-trispyrenylphenylamine (TPyPA), have been designed, synthesized and applied as hole-transporting emitters in organic light-emitting devices (OLEDs). While the two compounds have similar chemical structures (the only difference being the number of pyrene arms), devices based on them show distinct electroluminescent characteristics. PyTPA-based devices exhibit intense deep-blue emission with Commission Internationale de L'Eclairage coordinates (CIE) of (0.14, 0.11); whilst TPyPA-based devices emit white light with CIE of (0.31, 0.35). It is considered that the three electron-donating pyrene arms in TPyPA increase its electron-donating ability, which facilitates exciplex formation with the electron-transporter. This gives rise to a yellow exciplex emission and thus shifts the electroluminescence from deep-blue to white. More importantly, both devices can operate at record-low driving voltages (<4V at 20 mA cm−2), indicating the TPA-cored emitters offer not only high luminance efficiencies, but also good hole-injection and transporting features.

Mechanism of Cs2CO3 as an n-type dopant in organic electron-transport film

Abstract: The electronic structures of cesium carbonate (Cs2CO3) doped 4,7-diphenyl-1,10-phenanthroline (BPhen) films with various doping concentration are characterized by in situ ultraviolet and x-ray photoelectron spectroscopies, in an attempt to understand the mechanism of electron-transport enhancement in Cs2CO3-doped organic electron-transport layer for organic optoelectronic devices. The n-type electrical doping effect is evidenced by the Fermi level shift in the Cs2CO3-doped BPhen films toward unoccupied molecular states with increasing doping concentration, leading to increase in electron concentration in the electron-transport layer and reduction in electron injection barrier height. These findings originate from energetically favorable electron transfer from Cs2CO3 to BPhen.

Highly Luminescent Water-Dispersible Silicon Nanowires for Long-Term Immunofluorescent Cellular Imaging†

Abstract: Hybrid nanomaterials that incorporate different classes of nanostructures, such as nanoparticles, nanowires, and nanotubes, have been intensively studied, both in theory and application. Compared to a unitary nanostructure, nanohybrids feature many attractive merits. For example, desirable properties can be rationally designed by tailoring the architecture of nanohybrids, which are significant for fundamental understanding of the relationship between physical/ chemical properties and nanostructures. Moreover, multifunctional nanohybrids can be prepared by combinations of nanostructures of with unique merits to address various applications. Silicon nanostructures have shown great promise for various applications owing to their unique optical/electronic/catalytic properties, convenient surface functionality, and compatibility with silicon technologies, etc. For example, silicon-based nanohybrids made of silicon nanowires (SiNWs) decorated with noble-metal nanoparticles (for example Au, Ag, Pt) have been recently developed and utilized for solar cells, catalysts, and chemical/biological sensors. Herein, we present a novel kind of multicolor quantumdot (QD)-decorated SiNW, which are directly prepared in the aqueous phase by a facile one-pot strategy assisted by microwave irradiation. Remarkably, the SiNWs exhibit strong fluorescence (quantum yield of ca. 30–35%) with controllable emission wavelengths of 520–620 nm and excellent photostability, and they are well-suited to long-term and real-time immunofluorescent cellular imaging. Figure 1a presents a representation of our synthetic strategy. In brief, SiNWs are first modified by 3-mercaptopropionic acid (MPA) molecules (A!B) at 100–160 8C by microwave-induced

Controllable Fabrication of Three-Dimensional Radial ZnO Nanowire/Silicon Microrod Hybrid Architectures

Abstract: A facile method by combining bottom-up and top-down approaches was developed to construct uniform three-dimensional (3D) ZnO nanowires (NWs)/silicon microrod (SiMR) hybrid architectures. Patterned SiMR arrays with controlled geometry and density were structured by photolithography and chemical etching on single-crystal silicon wafers, which subsequently served as 3D scaffolds for the ZnO NW growth. In contrast to the top-down approach to fabricate SiMR scaffolds, the radial ZnO NWs grown conformally on the SiMRs follow a bottom-up method by employing a modified carbon-assisted self-catalytic growth via chemical vapor deposition. The light absorption and the photocatalytic capability of methyl red of ZnO NW arrays were demonstrated to improve significantly by the 3D constructions. The method is expected to be applicable to the synthesis of 3D hybrid structures of other nanomaterials. The heterojunction and ultralarge surface area of the 3D architectures are promising for diverse applications in photovoltai...

Enhanced performance in polymer photovoltaic cells with chloroform treated indium tin oxide anode modification

Abstract: Enhanced performance of a poly(3-hexylthiophene):(6,6)-phenyl C61 butyric acid methyl ester bulk heterojunction polymer photovoltaic cell is reported by modifying the indium tin oxide (ITO) anode with chloroform solution. Instead of the traditional UV-ozone treatment, the optimized chloroform modification on ITO anode can result in an enhancement in the power conversion efficiency of an identical device, originating from an increase in the photocurrent with negligible change in the open-circuit voltage. The performance enhancement is attributed to the work function modification of the ITO substrate through the surface incorporation of the chlorine, and thus improved charge collection efficiency.

Reductive Self-Assembling of Ag Nanoparticles on Germanium Nanowires and Their Application in Ultrasensitive Surface-Enhanced Raman Spectroscopy

Abstract: Silver nanoparticles (AgNPs) have been reductively fabricated on the hydrogen-terminated surface of germanium nanowires (GeNWs), which exhibited moderate reactivity toward the direct reduction of Ag (I) ion to metal nanoparticles in aqueous solution at room temperature. The electronic properties of the AgNPs/GeNWs system have been studied by X-ray photoelectron spectroscopy. The Ag nanoparticle-embedded germanium nanowires have been used as a unique surface-enhanced Raman scattering substrate, which could achieve the single molecule detection. The observed enhancement factor of the fabricated AgNPs/GeNWs substrate was estimated to be 107.

Silicon nanowires with permanent electrostatic charges for nanogenerators.

Abstract: Electrets are dielectric materials possessing a quasi-permanent electric charge or dipole polarization. Frequently, the electrets are adversely affected by environmental temperature and humidity, leading to charge instability, which severely restricts applications. Here we show that silicon nanowires (SiNWs) via modified oxide-assisted growth can surprisingly serve as electrets with permanent electrostatic charges and surface potential up to 7.7 mV. Significantly, the extraordinary electret behavior of SiNWs is extremely robust, remaining stable against immersion in water for over 2 months. The SiNWs were utilized to fabricate a nanogenerator, which yielded an output electrical power of 2.19 × 10–11 W with a conversion efficiency of 2.2%. The nanogenerator consists of only one movable part, giving highly sustainable and stable output signals, and thus holds promise for various self-powered applications. The permanent electrostatic charges on SiNWs are attributed to the formation of α-quartz in SiNWs.