Ultrasensitive Fluorescence Detection of Alzheimer's Disease Based on Polyvalent Directed Peptide Polymer Coupled to a Nanoporous ZnO Nanoplatform.

Amyloid-beta 42 (Aß42), the key biomarker of Alzheimer's disease (AD), aggregates to form neurotoxic amyloid plaques. In this work, we modified two fluorescein isothiocyanate-labeled Aß42-targeting peptides and designed an Aß42-specific ultrasensitive polyvalent-directed peptide polymer (PDPP) to enhance AD diagnosis sensitivity. The dissociation constant of Aß42 by PDPP was 103-fold higher than the single-site-directed peptide. The improved binding was due to the ability of PDPP to detect multiple receptors on the target. The power of the PDPP diagnostic probe was verified in its application to detect Aß42 in cerebrospinal fluid (CSF), which showed a lower limit of detection (LOD) in the fg mL-1 range that is more sensitive than detection by antibodies or single peptides. In addition, we present a novel ultrasensitive diagnostic system using an array of nanoporous ZnO nanoparticles, which play a role in fluorescence signal amplification, to further improve AD diagnosis sensitivity. We enhanced the signal on the basis of the properties of nanoporous ZnO nanoparticles and measured and quantified an ultralow concentration (ag mL-1 range) of Aß42. This PDPP coupled to the nanoporous ZnO-based system is a novel approach to AD diagnosis that might also be useful for the detection of other target biomarkers and clinical applications.

Copper-Organic Framework Fabricated with CuS Nanoparticles: Synthesis, Electrical Conductivity, and Electrocatalytic Activities for Oxygen Reduction Reaction.

To apply electrically nonconductive metal-organic frameworks (MOFs) in an electrocatalytic oxygen reduction reaction (ORR), we have developed a new method for fabricating various amounts of CuS nanoparticles (nano-CuS) in/on a 3D Cu-MOF, [Cu3 (BTC)2 ⋅(H2 O)3 ] (BTC=1,3,5-benzenetricarboxylate). As the amount of nano-CuS increases in the composite, the electrical conductivity increases exponentially by up to circa 109 -fold, while porosity decreases, compared with that of the pristine Cu-MOF. The composites, nano-CuS(x wt %)@Cu-BTC, exhibit significantly higher electrocatalytic ORR activities than Cu-BTC or nano-CuS in an alkaline solution. The onset potential, electron transfer number, and kinetic current density increase when the electrical conductivity of the material increases but decrease when the material has a poor porosity, which shows that the two factors should be finely tuned by the amount of nano-CuS for ORR application. Of these materials, CuS(28 wt %)@Cu-BTC exhibits the best activity, showing the onset potential of 0.91 V vs. RHE, quasi-four-electron transfer pathway, and a kinetic current density of 11.3 mA cm-2 at 0.55 V vs. RHE.

Optical and structural properties of plasma-treated ZnO nanostructures.

We studied the effect of plasma treatment on the structural and optical properties of ZnO nanostructures prepared by chemical bath deposition in an aqueous solution of Zn(NO3)2 and hexamethylenetetramine. The room-temperature photoluminescence (PL) spectrum of the as-grown ZnO nanostructures exhibited two emission bands due to exciton emission and defect emission. After treating with hydrogen plasma, the treated ZnO nanostructures exhibited stronger exciton emission than the as-grown, untreated ZnO nanostructures in their respective cathodoluminescence and PL spectra. The low-temperature PL spectrum of the hydrogen plasma-treated ZnO nanostructures showed a strong exciton emission at 3.34 eV, attributing to the bound exciton and its longitudinal optical-phonon sidebands. The strong exciton emission is thought to be due to the combined effect of exciton emission enhancement by defect passivation and optical confinement resulting from nanostructure geometry.

Direct detection of sulfide ions [S2-] in aqueous media based on fluorescence quenching of functionalized CdS QDs at trace levels: analytical applications to environmental analysis.

A novel, simple but highly selective fluorescent probe is developed for the direct detection of sulfide ions [S(2-)] based on the fluorescence quenching of the functionalized CdS QDs in aqueous solution at trace levels and successfully applied for quantitation of S(2-) from water samples in a complex matrix exclusive of pretreatment by standard addition method.

Escalating Catalytic Activity for Hydrogen Evolution Reaction on MoSe2@Graphene Functionalization.

Developing highly efficient and durable hydrogen evolution reaction (HER) electrocatalysts is crucial for addressing the energy and environmental challenges. Among the 2D-layered chalcogenides, MoSe2 possesses superior features for HER catalysis. The van der Waals attractions and high surface energy, however, stack the MoSe2 layers, resulting in a loss of edge active catalytic sites. In addition, MoSe2 suffers from low intrinsic conductivity and weak electrical contact with active sites. To overcome the issues, this work presents a novel approach, wherein the in situ incorporated diethylene glycol solvent into the interlayers of MoSe2 during synthesis when treated thermally in an inert atmosphere at 600 °C transformed into graphene (Gr). This widened the interlayer spacing of MoSe2, thereby exposing more HER active edge sites with high conductivity offered by the incorporated Gr. The resulting MoSe2-Gr composite exhibited a significantly enhanced HER catalytic activity compared to the pristine MoSe2 in an acidic medium and demonstrated a superior HER catalytic activity compared to the state-of-the-art Pt/C catalyst, particularly at a high current density beyond ca. 55 mA cm-2. Additionally, the MoSe2-Gr catalyst demonstrated long-term electrochemical stability during HER. This work, thus, presents a facile and novel approach for obtaining an efficient MoSe2 electrocatalyst applicable in green hydrogen production.

In situ polymerization of acetylene polymer on single-walled carbon nanotube and its application to photoinduced charge transfer system.

An acetylene polymer is formed on single-walled carbon nanotubes (SWNTs) using in situ polymerization. The acetylene polymers/SWNTs composite is hydrophilic even water-soluble, and has a structure of donor/acceptor dyad. In measurements of photocurrents-voltage curves, the composite film exhibits a power conversion efficiency of 1.50 x 10(-2%) under illumination (I = 80 mW/cm2, air mass 1.5 condition).

Structural and optical properties of chemically deposited CuInSe2 thin film in acidic medium.

Thin films of nanocrystalline CuInSe2 were prepared on glass substrates using chemical bath deposition in acidic medium at room temperature. Thickness of the chemically deposited CuInSe2 thin films was approximately 100 nm which composed of closely packed irregular grains of approximately 100-120 nm in diameter. X-ray diffraction pattern of CuInSe2 thin films showed nanocrystalline structure with (112) preferential orientation. The films exhibited faint black and direct band gap energy was 0.96 eV.

Enhancement of photoconversion efficiency of ZnO nanorod-based dye-sensitized solar cells in presence of ZrO2 thin energy barrier.

In order to enhance the power conversion efficiency of ZnO nanorods-based dye-sensitized solar cells (DSSCs), ZrO2 thin energy barriers were formed on ZnO nanorods using a sol-gel method. In DSSCs, the short-circuit current was substantially increased, and the dark current was significantly reduced in the presence of the ZrO2 layer. Due to suppressed recombination in the presence of the ZrO2 layer, 81.3% increment of power conversion efficiency is achieved compared to those without ZrO2 layer.

Enhanced photocurrent generation of binary self-assembled monolayers of di-(3-aminopropyl)-viologen and methylviologen on indium tin oxide.

The binary self-assembled monolayers (SAMs) of di-(3-aminopropyl)-viologen (DAPV) and methylviologen (MV) molecules on indium tin oxide (ITO) were prepared by dipping the DAPV SAMs/ITO substrates into MV solution. The DAPV-MV SAM films were characterized by UV-vis. absorption spectroscopy, Rutherford backscattering spectroscopy, and cyclic voltammetry. Optical band gap, lowest unoccupied molecular orbital, and highest occupied molecular orbital of DAPV-MV SAMs were measured to be 1.6, -4.3, and -5.9 eV, respectively. We found that although DAPV SAMs have a quantum yield of 0.11%, the binary SAM films have a good quantum yield of 2.30%, which was 20 times higher than that of DAPV SAMs on ITO. This result may be due to the higher adsorption property of the binary SAMs for the light in visible range compared to that of DAPV SAMs. From this study, we demonstrated that the photocurrent generation systems with a high quantum yield can be obtained by the functional binary SAMs.

Photoelectrochemical polymerization of thiophene on self-assembled RuL2(NCS)2/di(3-aminopropyl)viologen on indium thin oxide.

Polythiophene layers were formed on self-assembled monolayers (SAMs)/indium tin oxide (ITO) using photoelectrochemical polymerization. The SAMs on ITO was prepared using Ru(4,4'-dicarboxylic acid-2,2'-bipyridine)2(NCS)2 and di(3-aminopropyl)viologen. The photoelectrochemically polymerized polythiophene layers on SAMs/ITO were characterized using UV-vis. absorption spectroscopy, atomic force microscopy, scanning electron microscopy, and cyclic voltammetry. The polymer layers have thickness of 360 nm, a dense surface morphology, optical gap of 2.38 eV, highest occupied molecular orbital of -5.2 eV and lowest unoccupied molecular orbital of -2.82 eV. In photoelectrochemical cells, the polythiophene on SAMs/ITO electrode showed a photocurrent of 5 microA/cm2.

ZnO-CdS core-shell quantum dots sensitized solar cell: influence of crystalline and amorphous CdS structures in photovoltaic performance.

ZnO nanoparticles (NPs) coated with amorphous and crystalline CdS quantum dots (QDs) were successfully synthesized through chemical bath deposition (CBD) process. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) have been utilized to characterize the samples morphology and structural properties. The conduction band of CdS QDs is much higher than the ZnO conduction band facilitates electron transfer process through cascade system. The thickness and crystallinity of the CdS QDs coated on ZnO NPs critically controls the electron diffusion length and photovoltaic performance of the solar cell. The red shift from 506 to 524 nm, increased optical absorption in the UV-visible range and electron diffusion length limited by the thickness of the amorphous/crystalline CdS QDs coated on ZnO NPs film, influences the performance of the QDs sensitized solar cell (QDSSCs) under one sun illumination intensity (AM 1.5, 100 mW/cm2). The results discuss the CBD process controlled growth of CdS QDs on ZnO NPs and its influence on the photovoltaic performance of QDSSCs.

PH dependent morphological evolution of beta-Bi2O3/PANI composite for supercapacitor applications.

Crystalline beta-Bi2O3 was synthesized through pH-dependent chemical bath deposition process, altering the morphology and evolution from nanoparticles (approximately 40 nm) at pH 9 to platelets (approximately 40 nm width and 0.8 microm length) at pH 12. In-situ aniline nucleation and growth at less basic condition on the beta-Bi2O3 increased the surface area and specific capacitance of the device. The morphological change of beta-Bi2O3/PANI composite from nanoparticles to platelets like nanostructure facilitated higher specific capacitance from 210 to 430 F/g at a scan rate of 10 mV/s with enhanced ionic diffusion and retention of specific capacitance up to 84% at higher scan rates.

Effects of seed layers on structural, morphological, and optical properties of ZnO nanorods.

We studied the effects of seed layers on the structural and optical properties of ZnO nanorods. ZnO and Ag-doped ZnO (ZnO:Ag) seed layers were deposited on glass substrates by magnetron co-sputtering. ZnO nanorods were grown on these seed layers by the chemical bath deposition in an aqueous solution of Zn(NO3)2 and hexamethyltetramine. SEM micrographs clearly reveal that ZnO nanorods were successfully grown on both kinds of seed layers. The XRD patterns indicate that crystallization of ZnO nanorods is along the c-axis. Meanwhile, the packing density and the vertical alignment of the ZnO nanorods on the ZnO seed layer are better than those of the ZnO nanorods on ZnO:Ag. The enhanced growth of nanorods is thought to be due to the fact that the ZnO layer exhibits a higher crystalline quality than the ZnO:Ag layer. According to the low-temperature photoluminescence spectra, the ZnO nanorods on the ZnO seed layer show a narrow strong ultraviolet emission band centered at 369 nm, while those on ZnO:Ag exhibit multiple bands. These results are thought to be related with the crystallinity of ZnO nanorods, the morphologies of ZnO nanorods, and the reflectivities of seed layers. More detailed studies for clarification of the seed layer effect on the growth of ZnO nanorods are desirable.

Stereospecific growth of densely populated rutile mesoporous TiO2 nanoplate films: a facile low temperature chemical synthesis approach.

We report for the first time, using a simple and environmentally benign chemical method, the low temperature synthesis of densely populated upright-standing rutile TiO(2) nanoplate films onto a glass substrate from a mixture of titanium trichloride, hydrogen peroxide and thiourea in triply distilled water. The rutile TiO(2) nanoplate films (the phase is confirmed from x-ray diffraction analysis, selected area electron diffraction, energy-dispersive x-ray analysis, and Raman shift) are 20-35 nm wide and 100-120 nm long. The chemical reaction kinetics for the growth of these upright-standing TiO(2) nanoplate films is also interpreted. Films of TiO(2) nanoplates are optically transparent in the visible region with a sharp absorption edge close to 350 nm, confirming an indirect band gap energy of 3.12 eV. The Brunauer-Emmet-Teller surface area, Barret-Joyner-Halenda pore volume and pore diameter, obtained from N(2) physisorption studies, are 82 m(2) g(-1), 0.0964 cm(3) g(-1) and 3.5 nm, respectively, confirming the mesoporosity of scratched rutile TiO(2) nanoplate powder that would be ideal for the direct fabrication of nanoscaled devices including upcoming dye-sensitized solar cells and gas sensors.

Protective antigen detection using horizontally stacked hexagonal ZnO platelets.

Anthrax toxin detection before bacteremia, when toxin concentration is low, improves the chances of efficient treatment and cure. We present a novel technique for ultrasensitive detection of a protective antigen (PA(83)) of anthrax using an array of zinc oxide nanorods in conjunction with a FITC-labeled PA affinity peptide. The nanorods are composed of horizontally stacked hexagonal platelets which are uniformly spaced and grown unidirectionally upon a glass substrate via a new and simple technique. Images taken under UV emission demonstrate fluorescence sensitivity to PA as a function of antigen concentration, and a negative control using bovine serum albumin produced no fluorescence signal. The fluorescence signal of the PA-peptide complex is also significantly reduced in the absence of the nanorods, suggesting that the presence of ZnO nanorods inhibits the self-quenching properties of the fluorophore. A lower limit of detection for the assay system for PA is estimated at 150 aM, which demonstrates the possibility of using ZnO nanorods in biological sensor systems.

TiO2 nanotubes with a ZnO thin energy barrier for improved current efficiency of CdSe quantum-dot-sensitized solar cells.

This paper reports the formation of a thin ZnO energy barrier between a CdSe quantum dot (Q dots) sensitizer and TiO2 nanotubes (TONTs) for improved current efficiency of Q dot-sensitized solar cells. The formation of a ZnO barrier between TONTs and the Q dot sensitizer increased the short-circuit current under illumination and also reduced the dark current in a dark environment. The power conversion efficiency of Q dot-sensitized TONT solar cells increased by 25.9% in the presence of the ZnO thin layer due to improved charge-collecting efficiency and reduced recombination.

Electrochemically intercalated indium-tin-oxide/poly(3-hexylthiophene): A solid-state heterojunction solar cell.

A heterojunction solar cell design composed of poly(3-hexylthiophene) (P3HT) and intercalated indium-tin-oxide (ITO) donor-acceptor system is explored for the first time. Substantial change in band edge of ITO is noticed after intercalation. Structural and surface morphological studies are reported. Due to tuned band gap of ITO, an increase in short circuit current from 0.0012 to 0.46 mA/cm(2), fill factor from 0.39 to 0.51, and power conversion efficiency from 0.000 367 to 0.3% is obtained for heterojunction solar cell when compared to P3HT alone. This novel, room temperature design approach would be of great scientific interest in current solid-state solar cell scenario.

Enhanced photocurrent in the RuL2(NCS)2/ di-(3-aminopropyl)-viologen/Au nanoparticles/ITO system: use of Au nanoparticles for retardation of the back electron transfer reaction.

This paper reports the use of Au nanoparticles (NPs) as electron transfer bridge layers to improve the photocurrent of viologen/Ru complex-based photoelectrochemical cells. The Ru complex/ viologen/Au NPs on electrodes were prepared using self-assembled monolayers. The cell system showed an excellent photocurrent of 25 nA/cm2 under the 1.5 air mass condition (I = 100 mW/cm2), which is five times greater than Au NPs due to the reduced recombination reaction.

Reduced recombination and photodegradation processes of photoelectrochemical cell-based on CdSe nanofibers in the presence of PEDOT:PSS layers.

This paper reports the use of poly(3,4-ethylenedioxythiophen):poly(styrene sulfonate) (PEDOT: PSS) as a protective layer to reduce the photodegradation and recombination processes of CdSe nanofiber films. Due to reduced photodegradation and recombination processes of photoelectrochemical cell-based CdSe nanofiber films, the power conversion efficiency of CdSe nanofibers films was 1.81% in the presence of PEDOT:PSS layers under the 1.5 air mass condition (I = 80 mW/cm2), which is an 82.8% increase compared to films without PEDOT:PSS layers. Furthermore, the CdSe film was highly stable under illumination in the presence of PEDOT:PSS layers.

Improvement of device efficiency by phosphorescent materials in polymers bulk heterojunction solar cells.

To improve the performance of organic solar cells, various methods have been used to increase the light absorbance and electron transfer efficiency or decrease the internal resistance of the device. In this article, red dyes of phosphorescent materials are used to improve the performance of bulk heterojunction organic solar cells based on MDMO-PPV and PCBM. Solar cell devices doped with different red dyes showed higher performances in terms of current, voltage and conversion efficiency than those without red dyes. The efficiency was maximized in the devices with a 10% concentration of red dye 2, which was attributed to the longer exciton lifetimes that were induced by the triplet spin state of the red dyes allowing them to reach the p-n junction and thereby generate more photocurrent.