Marked difference in self-assembly, morphology, and cell viability of positional isomeric dipeptides generated by reversal of sequence.

In this study two positional isomeric dipeptides Boc-m-ABA-Aib-OMe () and Boc-Aib-m-ABA-OMe () synthesized by reversal of the positions of two rigid amino acids (m-ABA: m-aminobenzoic acid, Aib: α-aminoisobutyric acid) showed marked difference in morphology under the same environmental conditions. Investigation of single crystal structures reveals the difference in crystal packing and higher order self-assembly pattern for both the isomeric peptides, which might be the responsible factor for their different morphological patterns. Moreover, these isomeric dipeptides have produced different cellular viability effects towards normal bone cells. These two peptides would have utilities in the model study of isomeric peptides/proteins, where morphological difference under identical conditions brings changes in their individual bio-activities and where the reversal of sequence causes different cellular viability and generates health hazard.

A simple N,N'-dicyclohexylurea adduct of ß-alanine can self-assemble to generate nano-morphological versatility in response to different environmental conditions.

A single ω-amino acid based molecule "Boc-ß-Ala-N,N'-dicyclohexylurea" can form diverse nanostructures such as nano-vesicles, nano-tubes, nano-rods and nano-fibrils by self-assembly, in response to various environmental conditions. Interestingly, the nano-vesicular structures generated from this molecule can encapsulate the highly potent anticancer drug methotrexate, which can be released by salt triggered disruption of these vesicles. This phenomenon indicates the probability of its use in targeted delivery of drugs or any bio-active molecule, utilizing this encapsulation efficiency. Moreover, a surface-induced morphological transformation of these nano-vesicles to nano-fibers can be realized while they interact with hydrocarbon-functionalized surfaces. This phenomenon indicates the probability of their utilization in model study of peptide interaction behavior at liquid-solid interfaces and can be used in advanced study of various biological phenomena and bio-technological applications.

Location-Selective Work Function Engineering by Self-Assembled Monolayers.

Control over specific interfaces in devices represents a key challenge for modern organic electronics and photovoltaics. Such control is frequently gained by the use of self-assembled monolayers (SAMs), which, by selection of a proper anchoring group, are generally discriminative with respect to different materials but are not selective between different areas of the same material. In particular, selective tailoring of the work function may be useful for different functional devices in a circuit. Here we demonstrate an approach for solving this problem, opening a way to function-selective electrostatic engineering of chemically identical areas, such as source and drain electrodes in a specific type of organic transistor and, more importantly, the electrodes in different types of organic devices, such as p- and n-channel transistors, located on the same circuitry board. The approach is based on the ultraviolet-light-promoted exchange reaction of SAMs on gold, a standard electrode material in organic electronics.

Effect of surface plasmon resonance on the photocatalytic activity of Au/TiO2 under UV/visible illumination.

In this study, gold-loaded titanium dioxide was prepared by an impregnation method to investigate the effect of surface plasmon resonance (SPR) on photoactivity. The deposited gold nanoparticles (NPs) absorb visible light because of SPR. The effects of both the gold content and the TiO2 size of Au/TiO2 on SPR and the photocatalytic efficiency were investigated. The morphology, crystal structure, light absorption, emission from the recombination of a photoexcited electron and hole, and the degree of aggregation were investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-visible-diffuse reflectance spectra (UV-VIS-DRS), photoluminescence (PL) spectroscopy, and turbidimetry, respectively. Photocatalytic activity was evaluated by the decolorization of methyl orange solution over modified titania under UV and UV/GLED (green light emitting diode) illumination. Au/TiO2 NPs exhibited an absorption peak (530-570 nm) because of SPR. The results of our photocatalytic experiments indicated that the UV-inducedly photocatalytic reaction rate was improved by simultaneously using UV and green light illumination; this corresponds to the adsorption region of SPR. Au/TiO2 could use the enhanced electric field amplitude on the surface of the Au particle in the spectral vicinity of its plasmon resonance and thus improve the photoactivity. Experimental results show that the synergistic effect between UV and green light for the improvement of photoactivity increases with increasing the SPR absorption, which in turn is affected by the Au content and TiO2 size.

Direct formation of platinum nanoparticles by internally isopropanol-modified dendritic poly(amido amine).

We report a reducing agent-free method for preparing platinum (Pt) nanoparticles by internally isopropanol (IPA)-modified dendritic poly(amido amine) (PAMAM). The internally modified dendritic PAMAM were synthesized via divergent strategy using 1,3-diaminopropanol as a linking spacer, and NMR analyses confirm the embedded IPA moieties within the dendrimers by the appearance of characteristic proton and carbon resonances at 3.81 and 67.9 ppm, respectively. The in situ formation of stable Pt colloids was carried out by thermal treatment in the presence of internally modified dendritic PAMAM bearing either ester or alcohol peripherals, suggesting that the internal IPA functionalities dominate the reduction of Pt4+ ions. Moreover, the overall reducing rate was accelerated with increasing pH values. This result agreed with a reaction feature for preparing metal nanocomposites through polyol process in which basic environment facilitates the thermal-promoted reduction of metal ions accompanied with the oxidation of internal hydroxyl groups. The morphology of the dendrimer/Pt composite monitored by a transmission electron microscope (TEM) exhibited narrowly dispersed and roughly spherical shaped nanoparticles with a mean diameter of 5.4 nm.

Direct synthesis of Rev peptide-conjugated gold nanoparticles and their application in cancer therapeutics.

We have developed a simple approach for generating peptide-conjugated gold nanoparticles (AuNPs) from the Rev peptide and gold aqueous solution. The peptide functions as both a reducing agent and a capping molecule. AuNPs of various sizes (20-300 nm) and shapes (spheres, triangular plates, and polygons) can be obtained upon modulating the ratio of gold ions to the Rev peptide. Transmission electron microscopy, X-ray diffraction, and UV-vis spectroscopy were utilized to characterize these nanoparticles. Fourier-transform infrared and X-ray photoelectron spectroscopy measurements were performed to investigate chemical interactions between the Rev peptide and AuNPs. Lactate dehydrogenase and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays revealed that the Rev peptide-AuNP nanocomposites exhibited exceptionally high cytotoxic effects toward mouse ovarian surface epithelial cell lines, relative to the effects of equal doses of the free Rev peptide. Our study suggests a new way of utilizing biomolecule-conjugated AuNPs as potentially effective anticancer drugs.

Antireflective silicon surface with vertical-aligned silicon nanowires realized by simple wet chemical etching processes.

Silicon antireflection is realized with vertical-aligned SiNWs by using improved metal-induced etching technique. The spectral responses of the transmission, reflection, and absorption characteristics for the SiNWs of different lengths are investigated. In order to realize short SiNWs to provide sufficiently low reflection, a post chemical etching process is developed to make the nanowires have a larger length fluctuation and/or tapered structure. The use of short SiNWs can allow a faster process time and avoid the sub-bandgap absorption that frequently occurs in long nanowires. Short SiNWs can also provide more compatible material structure and fabrication procedures than long ones can for applying to make optoelectronic devices. Taking the applications to solar cells as examples, the SiNWs fabricated by the proposed technique can provide 92% of solar weighted absorption with about 720 nm long wires because of the resultant effective graded index and enhanced multiple optical scattering from the random SiNW lengths and tapered wires after KOH etching.

Improved charge separation properties of organic hetero-junction solar cells by self-assembled monolayers anchored Ag nanoparticles.

We investigate the effect of self-assembled monolayers and localized surface plasmons of silver nano-particles on an organic solar cell consisting of zinc phthalocyanine as an active layer. The device was fabricated by covalent attachment of silver nanoparticles on n-type silicon substrates using self-assembled monolayer of 4-mercaptophenol. Power conversion efficiency is increased up to 8 times as compared to a reference device with merely 0.13% photo-conversion efficiency containing no self-assembled monolayers and silver nano-particles. We believe that improved conductivity at the interface due to the aromatic self-assembled monolayer and the increased local electric field experienced by the active layer in presence of silver nano-particles act in synergy towards the higher population of excitons and dissipation of charge.

Discriminate crystallinities of tin doped indium oxide films on self-assembled monolayers modified glass substrates.

Tin doped indium oxide (ITO) films have generated tremendous research interest and received widespread applications in optoelectronic devices due to a good combination of desired optical and electrical properties. Their electrical properties vary depending on the crystallinity of the film. A good quality ITO film should have low resistivity, which can be achieved with highly crystalline films deposited at very high temperature. Thus, film quality is sensitive to the deposition conditions. Generally, low-temperature deposition of ITO results in poor quality films due to amorphous growth. In this study, we have demonstrated that crystallinity of the ITO films can be improved even at room temperature (RT) using self-assembled monolayers (SAMs) modified glass substrates. The present study demonstrates that SAM with -SH terminal group is necessary for the high-quality ITO growth, while SAMs with other terminal groups (-NH(2) and -CH(3)) generate ITO films with moderate crystallinity. Various properties of such films were investigated using X-ray diffraction, X-ray photoelectron depth profile, four-point probe, and Hall measurements. It is confirmed from such measurements that ITO film deposited on -SH terminated SAM substrate has excellent crystallinity, conductivity, and optical transmission.

Surface functionalization of carbon micro coils and their selective immobilization on surface-modified silicon substrates.

Surface functionalization of carbon micro coils (CMCs) was performed by acid treatment at different times. Nitric acid oxidation produced CMC with acidic functional groups, although morphology of CMCs was modified after the oxidation. The selective immobilization of as-prepared CMC from an aqueous dispersion was examined on differently surface-modified silicon substrates. It was confirmed that the acid-treated CMC was selectively immobilized on a silicon substrate by chemical bonding with amine-terminated self-assembled monolayers on a silicon substrate, while the pristine CMC was not.

Unraveling the critical effects of the preoxidation process toward the morphological evolution and intrinsic properties of novel ZnCoMn trimetallic hydroxides.

A strategy for simultaneously preparing and modulating the morphological structure evolution and physical properties of novel trimetallic hydroxides is introduced. The interrelations among the level of pre-oxidation, the nanostructure evolution and the physicochemical properties of the material are thoroughly investigated. In addition, the growth mechanism for this new type of ternary hydroxide is also proposed. This work provides not only a convincing demonstration of a novel composite being used as a cheap and promising material for energy conversion, but also an effective method for rationally designing other hydroxide-based materials.

Fully Ambient-Processed Perovskite Film for Perovskite Solar Cells: Effect of Solvent Polarity on Lead Iodide.

Fully ambient-processed and highly efficient methylammonium lead iodide (MAPbI3) perovskite films are very desirable for industrial manufacturing of perovskite solar cells (PSCs). To date, most reported highly efficient MAPbI3 PSCs rely on the fabrication of lead iodide (PbI2) films inside the glovebox. Here we report a simple fabrication method using extra dry isopropanol (IPA100) for obtaining uniform and loosely packed PbI2 film, which leads to a uniform and highly crystalline MAPbI3 film under ambient conditions. Compared with recently reported results (10%-15%) using IPA treatment in the glovebox, we achieved over 16% efficiency of PSCs while fabricating perovskite films in fully ambient conditions. We have found the removal of even trace amounts of water from IPA to be a key factor for the successful ambient fabrication of PbI2 films, as the high polarity of water negatively influences the crystallinity and morphology of the PbI2 film.

Performance Characterization of Dye-Sensitized Photovoltaics under Indoor Lighting.

Indoor utilization of emerging photovoltaics is promising; however, efficiency characterization under room lighting is challenging. We report the first round-robin interlaboratory study of performance measurement for dye-sensitized photovoltaics (cells and mini-modules) and one silicon solar cell under a fluorescent dim light. Among 15 research groups, the relative deviation in power conversion efficiency (PCE) of the samples reaches an unprecedented 152%. On the basis of the comprehensive results, the gap between photometry and radiometry measurements and the response of devices to the dim illumination are identified as critical obstacles to the correct PCE. Therefore, we use an illuminometer as a prime standard with a spectroradiometer to quantify the intensity of indoor lighting and adopt the reverse-biased current-voltage (I-V) characteristics as an indicator to qualify the I-V sampling time for dye-sensitized photovoltaics. The recommendations can brighten the prospects of emerging photovoltaics for indoor applications.

Effect of irradiation dose in making an insulator from a self-assembled monolayer.

A combination of functionalization and irradiation-induced cross-linking allows fabrication of stable metal film on top of an aromatic self-assembled monolayer, [1,1';4',1' '-terphenyl]-4,4' '-dimethanethiol (TPDMT) on Au. Using X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and ion-scattering spectroscopy the optimal irradiation dose for producing a stable metal overlayer was estimated to be 40-45 mC/cm2. This dose is necessary for complete 2D-polymerization and closure of transient channels, which would otherwise allow metal penetration into the SAM. What is also important, the majority of the thiol tail groups, responsible for 2D growth and chemical adherence of the metal film, remains intact even at this high dose. The optimal dose corresponds to a crossover in the response of the TPDMT film to ionizing radiation: the irradiation-induced processes progress fast at lower doses and saturate at higher doses.

Electrochemical characterizations of nickel deposition on aromatic dithiol monolayers on gold electrodes.

The electronic properties of pristine and cross-linked (CL) self-assembled monolayers (SAMs) of [1,1';4',1' '-terphenyl]-4,4' '-dimethanethiol (TPDMT) on Au were studied by electrochemical measurements, including cyclic voltammetry and impedance spectroscopy. In addition, nickel deposition onto the TPDMT and CL-TPDMT substrates was investigated. In all cases, the TPDMT and CL-TPDMT films were found to be insulators, which effectively blocked the ionic permeation of electrolyte, preventing direct access of ions to the Au electrode. At the same time, CL-TPDMT is a better electric insulator than the pristine TPDMT SAM. The top Ni layer in the Ni/CL-TPDMT/Au arrangement was electrically isolated from the Au substrate, and no short circuits occurred. This layer was found to be conductive and relatively stable in the broad potential range in the electrolyte solution.

Edge promoted ultrasensitive electrochemical detection of organic bio-molecules on epitaxial graphene nanowalls.

We report the simultaneous electrochemical detection of dopamine (DA), uric acid (UA) and ascorbic acid (AA) on three dimensional (3D) unmodified 'as-grown' epitaxial graphene nanowall arrays (EGNWs). The 3D few layer EGNWs, unlike the 2D planar graphene, offers an abundance of vertically oriented nano-graphitic-edges that exhibit fast electron-transfer kinetics and high electroactive surface area to geometrical area (EAA/GA≈134%), as evident from the Fe(CN)6(3-/4-) redox kinetic study. The hexagonal sp(2)-C domains, on the basal plane of the EGNWs, facilitate efficient adsorption via spontaneous π-π interaction with the aromatic rings in DA and UA. Such affinity together with the fast electron kinetics enables simultaneous and unambiguous identification of individual AA, DA and UA from their mixture. The unique edge dominant EGNWs result in an unprecedented low limit of detection (experimental) of 0.033 nM and highest sensitivity of 476.2 µA/µM/cm(2), for UA, which are orders of magnitude higher than comparable existing reports. A reaction kinetics based modeling of the edge-oriented 3D EGNW system is proposed to illustrate the superior electro-activity for bio-sensing applications.

Study of the nano-morphological versatility by self-assembly of a peptide mimetic molecule in response to physical and chemical stimuli.

A small peptide mimetic molecule can form diverse nanostructures such as nano-vesicles, nano-tubes and nano-ribbons/fibrils by self-assembly, in response to various physical and chemical stimulations.

A bifunctional copolymer additive to utilize photoenergy transfer and to improve hole mobility for organic ternary bulk-heterojunction solar cell.

To realize the high efficiency organic photovoltaics (OPVs), two critical requirements have to be fulfilled: (1) increasing the photon energy absorption range of the active layer, and (2) improving charge separation and transport in the active layer. This study reports the utilization of THC8, a novel fluorescence-based polymer containing propeller-shaped di-triarylamine and fluorene moieties in the active layer consisting of poly-3-hexylthiophene and [6,6]-phenyl-C61-butyric acid methyl ester to form a ternary bulk heterojunction. The results showed that the high absorbance and strong fluorescence of THC8 at 420 and 510 nm, respectively, broadened the spectral absorption of the OPV, possibly through Förster resonance energy transfer. In addition, the morphology of the device active layer was improved with the addition of a suitable amount of THC8. Consequently, the charge transport property of the active layer was improved. The best power conversion efficiency (PCE) of the device with THC8 was 3.88%, a 25% increase compared to the PCE of a pristine OPV.

Improving the efficiency of ZnO-based organic solar cell by self-assembled monolayer assisted modulation on the properties of ZnO acceptor layer.

In this study, we fabricated a bilayer hybrid organic solar cell with P3HT as the donor and ZnO as the acceptor (ITO/ZnO/P3HT/Au). We show that passivating a self-assembled monolayer (SAM) over the ITO electrode surface before fabricating the ZnO layer improves the crystallinity of the ZnO layer and of the P3HT layer spin-coated on top of the ZnO layer. The SAM modification resulted in improved charge mobility in the ZnO and P3HT layers. As a consequence, the short circuit current of the photovoltaic device were enhanced. The power conversion efficiency of the SAM-modified device was approximately 60% higher than that of the untreated device. Our findings suggest that the performance of metal oxide-based organic solar cells can be improved by SAM-assisted modulation of metal oxide crystallinity.

Self-assembled monolayer immobilized gold nanoparticles for plasmonic effects in small molecule organic photovoltaic.

The aim of this study was to investigate the effect of gold nanoparticle (Au NP)-induced surface plasmons on the performance of organic photovoltaics (OPVs) that consist of copper phthalocyanine and fullerene as the active materials. The photon absorption can be enhanced by immobilization of surfactant-stabilized Au NPs on a self-assembled monolayer-modified indium tin oxide (ITO) electrode, and thus, the photocurrent as well as the power conversion efficiency (PCE) of these OPVs can be improved. Varying the density of the immobilized Au NPs in the devices provided no significant variation in the charge mobility but it did enhance the photocurrent. In addition, device simulation results demonstrated that the improvement in photocurrent was due to the enhancement of light absorption and the increase in charge separation, which was facilitated by the Au NPs. Overall, we attributed the improvement in PCE of OPVs to a localized surface plasmon resonance effect generated by the Au NPs.