Systematic modulation of quantum (electron) tunneling behavior by atomic layer deposition on nanoparticulate SnO2 and TiO2 photoanodes.

Ultrathin films of TiO2, ZrO2, and Al2O3 were conformally created on SnO2 and TiO2 photoelectrodes via atomic layer deposition (ALD) to examine their influence upon electron transfer (ET) from the electrodes to a representative molecular receptor, I3(-). Films thicker than 2 Å engender an exponential decrease in ET time with increasing film thickness, consistent with tunneling theory. Increasing the height of the barrier, as measured by the energy difference between the transferring electron and the bottom of the conduction band of the barrier material, results in steeper exponential drops in tunneling rate or probability. The variations are quantitatively consistent with a simple model of quantum tunneling of electrons through square barriers (i.e., barriers of individually uniform energy height) that are characterized by individually uniform physical thickness. The findings demonstrate that ALD is a remarkably uniform and precise method for modifying electrode surfaces and imply that standard tunneling theory can be used as a quantitative guide to intentionally and predictively modulating rates of ET between molecules and electrodes.

Dye stabilization and enhanced photoelectrode wettability in water-based dye-sensitized solar cells through post-assembly atomic layer deposition of TiO2.

Detachment (desorption) of molecular dyes from photoelectrodes is one of the major limitations for the long-term operation of dye-sensitized solar cells. Here we demonstrate a method to greatly inhibit this loss by growing a transparent metal oxide (TiO2) on the dye-coated photoelectrode via atomic layer deposition (ALD). TiO2-enshrouded sensitizers largely resist detachment, even in pH 10.7 ethanol, a standard solution for intentional removal of molecular dyes from photoelectrodes. Additionally, the ALD post-treatment renders the otherwise hydrophobic dye-coated surface hydrophilic, thereby enhancing photoelectrode pore-filling with aqueous solution.

Effective panchromatic sensitization of electrochemical solar cells: strategy and organizational rules for spatial separation of complementary light harvesters on high-area photoelectrodes.

Dye-sensitized solar cells, especially those comprising molecular chromophores and inorganic titania, have shown promise as an alternative to silicon for photovoltaic light-to-electrical energy conversion. Co-sensitization (the use of two or more chromophores having complementary absorption spectra) has attracted attention as a method for harvesting photons over a broad spectral range. If implemented successfully, then cosensitization can substantially enhance photocurrent densities and light-to-electrical energy conversion efficiencies. In only a few cases, however, have significant overall improvements been obtained. In most other cases, inefficiencies arise due to unconstructive energy or charge transfer between chromophores or, as we show here, because of modulation of charge-recombination behavior. Spatial isolation of differing chromophores offers a solution. We report a new and versatile method for fabricating two-color photoanodes featuring spatially isolated chromophore types that are selectively positioned in desired zones. Exploiting this methodology, we find that photocurrent densities depend on both the relative and absolute positions of chromophores and on "local" effective electron collection lengths. One version of the two-color photoanode, based on an organic push-pull dye together with a porphyrin dye, yielded high photocurrent densities (J(SC) = 14.6 mA cm(-2)) and double the efficiency of randomly mixed dyes, once the dyes were optimally positioned with respect to each other. We believe that the organizational rules and fabrication strategy will prove transferrable, thereby advancing understanding of panchromatic sensitization as well as yielding higher efficiency devices.

Glass-encapsulated light harvesters: more efficient dye-sensitized solar cells by deposition of self-aligned, conformal, and self-limited silica layers.

A major loss mechanism in dye-sensitized solar cells (DSCs) is recombination at the TiO(2)/electrolyte interface. Here we report a method to reduce greatly this loss mechanism. We deposit insulating and transparent silica (SiO(2)) onto the open areas of a nanoparticulate TiO(2) surface while avoiding any deposition of SiO(2) over or under the organic dye molecules. The SiO(2) coating covers the highly convoluted surface of the TiO(2) conformally and with a uniform thickness throughout the thousands of layers of nanoparticles. DSCs incorporating these selective and self-aligned SiO(2) layers achieved a 36% increase in relative efficiency versus control uncoated cells.

A Novel Efficient Piscine Oral Nano-Vaccine Delivery System: Modified Halloysite Nanotubes (HNTs) Preventing Streptococcosis Disease in Tilapia (Oreochromis sp.).

Generally, the injection method is recommended as the best efficient method for vaccine applications in fish. However, labor-intensive and difficult injection for certain fish sizes is always considered as a limitation to aquatic animals. To demonstrate the effectiveness of a novel oral delivery system for the piscine vaccine with nano-delivery made from nano clay, halloysite nanotubes (HNTs) and their modified forms were loaded with killed vaccines, and we determined the ability of the system in releasing vaccines in a mimic digestive system. The efficaciousness of the oral piscine vaccine nano-delivery system was evaluated for its level of antibody production and for the level of disease prevention in tilapia. Herein, unmodified HNTs (H) and modified HNTs [HNT-Chitosan (HC), HNT-APTES (HA) and HNT-APTES-Chitosan (HAC)] successfully harbored streptococcal bivalent vaccine with inactivated S. agalactiae, designated as HF, HAF, HCF and HACF. The releasing of the loading antigens in the mimic digestive tract demonstrated a diverse pattern of protein releasing depending on the types of HNTs. Remarkably, HCF could properly release loading antigens with relevance to the increasing pH buffer. The oral vaccines revealed the greatest elevation of specific antibodies to S. agalactiae serotype Ia in HCF orally administered fish and to some extent in serotype III. The efficacy of streptococcal disease protection was determined by continually feeding with HF-, HAF-, HCF- and HACF-coated feed pellets for 7 days in the 1st and 3rd week. HCF showed significant RPS (75.00 ± 10.83%) among the other tested groups. Interestingly, the HCF-treated group exhibited noticeable efficacy similar to the bivalent-vaccine-injected group (RPS 81.25 ± 0.00%). This novel nano-delivery system for the fish vaccine was successfully developed and exhibited appropriated immune stimulation and promised disease prevention through oral administration. This delivery system can greatly support animals' immune stimulation, which conquers the limitation in vaccine applications in aquaculture systems. Moreover, this delivery system can be applied to carrying diverse types of biologics, including DNA, RNA and subunit protein vaccines.

Impedimetric detection of 2,4,6-trinitrotoluene using surface-functionalized halloysite nanotubes.

Herein, we report the application of amine-surface-functionalized halloysite nanotubes (HAs) as active materials for the quantitative detection of 2,4,6-trinitrotoluene (TNT). The findings indicated that HA could selectively capture TNT via a strong reaction between the amine groups on its surface and the TNT molecules. Plate electrodes were fabricated from HA to evaluate its TNT-sensing capacity by electrochemical impedance spectroscopy. Upon binding with TNT, the proton conductivity on the HA plate electrodes increased linearly with the TNT concentration from 1.0 × 10-11 M to 1.0 × 10-4 M. The HA plate electrodes exhibited good sensitivity with a detection limit of 1.05 × 10-12 M. Subsequently, the cycling measurements of the TNT binding/removal were performed on the HA plate electrode, and the material exhibited high stability, good regenerative ability, and good reversibility without a significant decrease in efficiency. The present work highlights the significant application potential of HAs for the electrochemical detection of TNT.

Sensitive electrochemical sensor based on nickel/PDDA/reduced graphene oxide modified screen-printed carbon electrode for nitrite detection.

A simple, rapid method of the determination of nitrite in food samples is reported by using a highly sensitive electrochemical sensor based on nickel, poly(diallyldimethylammonium chloride) (PDDA), reduced graphene oxide (rGO) and a disposable screen-printed carbon electrode (SPCE). The method is based on a modification of the electrode to enhance the sensitivity and selectivity of the disposable and applicable SPCE, which is essential for the present analytical challenge. The nitrite determination was performed by using a cyclic voltammetry (CV) method under optimum conditions. Ni/PDDA/rGO/SPCE showed a linear working range of 6 to 100 µM of nitrite concentration. The limit of detection and limit of quantification were 1.99 µM (S/N = 3) and 6.6 µM (S/N = 10), respectively. The sensitivities were 0.453 µA µM-1 cm-2 for the lower concentration range and 0.171 µA µM-1 cm-2 for the higher concentration range. The Ni/PDDA/rGO sensor also showed excellent anti-interference ability and good long-term stability. The purposed disposable sensor was successfully applied to determine nitrite in sausages and pickled vegetable samples with satisfactory recovery.

Enhanced electrocatalytic reduction of CO2 with ternary Ni-Fe4S4 and Co-Fe4S4-based biomimetic chalcogels.

Enzymes that catalytically transform small molecules such as CO, formate, or protons are naturally composed of transition metal cluster units bound into a larger superstructure. Artificial biomimetic catalysts are often modeled after the active sites but are typically molecular in nature. We present here a series of fully integrated porous materials containing Fe(4)S(4) clusters, dubbed "biomimetic chalcogels". We examine the effect of third metal cations on the electrochemical and electrocatalytic properties of the chalcogels. We find that ternary biomimetic chalcogels containing Ni or Co show increased effectiveness in transformations of carbon dioxide and can be thought of as solid-state analogues of NiFe or NiFeS reaction centers in enzymes.

Photocurrent enhancement by surface plasmon resonance of silver nanoparticles in highly porous dye-sensitized solar cells.

Localized surface plasmon resonance (LSPR) by silver nanoparticles that are photochemically incorporated into an electrode-supported TiO(2) nanoparticulate framework enhances the extinction of a subsequently adsorbed dye (the ruthenium-containing molecule, N719). The enhancement arises from both an increase in the dye's effective absorption cross section and a modest increase in the framework surface area. Deployment of the silver-modified assembly as a photoanode in dye-sensitized solar cells leads to light-to-electrical energy conversion with an overall efficiency of 8.9%. This represents a 25% improvement over the performance of otherwise identical solar cells lacking corrosion-protected silver nanoparticles. As one would expect based on increased dye loading and electromagnetic field enhanced (LSPR-enhanced) absorption, the improvement is manifested chiefly as an increase in photocurrent density ascribable to improved light harvesting.

Self-Correcting Process for High Quality Patterning by Atomic Layer Deposition.

Nanoscale patterning of materials is widely used in a variety of device applications. Area selective atomic layer deposition (ALD) has shown promise for deposition of patterned structures with subnanometer thickness control. However, the current process is limited in its ability to achieve good selectivity for thicker films formed at higher number of ALD cycles. In this report, we demonstrate a strategy for achieving selective film deposition via a self-correcting process on patterned Cu/SiO2 substrates. We employ the intrinsically selective adsorption of octadecylphosphonic acid self-assembled monolayers on Cu over SiO2 surfaces to selectively create a resist layer only on Cu. ALD is then performed on the patterns to deposit a dielectric film. A mild etchant is subsequently used to selectively remove any residual dielectric film deposited on the Cu surface while leaving the dielectric film on SiO2 unaffected. The selectivity achieved after this treatment, measured by compositional analysis, is found to be 10 times greater than for conventional area selective ALD.

Post-assembly atomic layer deposition of ultrathin metal-oxide coatings enhances the performance of an organic dye-sensitized solar cell by suppressing dye aggregation.

Dye aggregation and concomitant reduction of dye excited-state lifetimes and electron-injection yields constitute a significant mechanism for diminution of light-to-electrical energy conversion efficiencies in many dye-sensitized solar cells (DSCs). For TiO2-based DSCs prepared with an archetypal donor-acceptor organic dye, (E)-2-cyano-3-(5'-(5''-(p-(diphenylamino)phenyl)-thiophen-2''-yl)thiophen-2'-yl)acrylic acid (OrgD), we find, in part via ultrafast spectroscopy measurements, that postdye-adsorption atomic layer deposition (ALD) of ultrathin layers of either TiO2 or Al2O3 effectively reverses residual aggregation. Notably, the ALD treatment is significantly more effective than the widely used aggregation-inhibiting coadsorbent, chenodeoxycholic acid. Primarily because of reversal of OrgD aggregation, and resulting improved injection yields, ALD post-treatment engenders a 30+% increase in overall energy conversion efficiency. A secondary contributor to increased currents and efficiencies is an ALD-induced attenuation of the rate of interception of injected electrons, resulting in slightly more efficient charge collection.

Improving area-selective molecular layer deposition by selective SAM removal.

Area selective molecular layer deposition (MLD) is a promising technique for achieving micro- or nanoscale patterned organic structures. However, this technique still faces challenges in attaining high selectivity, especially at large MLD cycle numbers. Here, we illustrate a new strategy for achieving high quality patterns in selective film deposition on patterned Cu/Si substrates. We employed the intrinsically selective adsorption of an octadecylphosphonic acid self-assembled monolayer (SAM) on Cu over Si surfaces to selectively create a resist layer only on Cu. MLD was then performed on the patterns to deposit organic films predominantly on the Si surface, with only small amounts growing on the Cu regions. A negative potential bias was subsequently applied to the pattern to selectively desorb the layer of SAMs electrochemically from the Cu surface while preserving the MLD films on Si. Selectivity could be enhanced up to 30-fold after this treatment.

Area selective molecular layer deposition of polyurea films.

Patterned organic thin films with submicrometer features are of great importance in applications such as nanoelectronics and optoelectronics. We present here a new approach for creating patterned organic films using area selective molecular layer deposition (MLD). MLD is a technique that allows for conformal deposition of nanoscale organic thin films with exceptional control over vertical thickness and composition. By expanding the technique to allow for area selective MLD, lateral patterning of the film can be achieved. In this work, polyurea thin films were deposited by alternating pulses of 1,4-phenylenediisocyanate (PDIC) and ethylenediamine (ED) in a layer-by-layer fashion with a linear growth rate of 5.3 Å/cycle. Studies were carried out to determine whether self-assembled monolayer (SAM) formed from octadecyltrichlorosilane (ODTS) could block MLD on silicon substrates. Results show that the MLD process is impeded by the SAM. To test lateral patterning in MLD, SAMs were patterned onto silicon substrates using two different approaches. In one approach, SiO2-coated Si(100) substrates were patterned with an ODTS SAM by soft lithography in a well-controlled environment. In the second approach, patterned ODTS SAM was formed on H-Si/SiO2 patterned wafers by employing the chemically selective adsorption of ODTS on SiO2 over H-Si. Auger electron spectroscopy results revealed that the polyurea film is deposited predominantly on the ODTS-free regions of both patterned substrates, indicating sufficient blocking of MLD by the ODTS SAM layer to replicate the pattern. The method we describe here offers a novel approach for fabricating high quality, three-dimensional organic structures.

Fast transporting ZnO-TiO2 coaxial photoanodes for dye-sensitized solar cells based on ALD-modified SiO2 aerogel frameworks.

A doubly coaxial photoanode architecture based on templated SiO(2) aerogels was fabricated on transparent conducting oxides for use in dye-sensitized solar cells (DSSCs). These templates were coated with ZnO via atomic layer deposition (ALD) to yield an electronically interconnected, low-density, high-surface-area, semiconductor framework. Addition of a thin conformal layer of a second metal oxide (alumina, zirconia, or titania) via ALD was found to suppress the dissolution of ZnO that otherwise occurs when it is soaked in alcohol solutions containing acidic dyes used for sensitization or in acetonitrile solutions containing a pyridine derivative and the iodide/tri-iodide (I(-)/I(-)(3)) redox shuttle. Electron transport in SiO(2)-ZnO-TiO(2) photoelectrodes was found to be nearly 2 orders of magnitude faster than in SiO(2)-TiO(2) structures, implying that the interior ZnO sheath serves as the primary electron conduit. In contrast, rates of electron interception by the oxidized form of the redox shuttle were observed to decrease when a TiO(2) shell was added to SiO(2)-ZnO, with the decreases becoming more significant as the thickness of the titania shell increases. These effects lead to improvements in efficiency for DSSCs that utilize I(-)/I(-)(3), but much larger improvements for DSSCs utilizing ferrocene/ferrocenium, a notoriously fast redox shuttle. For the former, overall energy conversion efficiencies maximize at 4.0%. From a variety of experiments, the primary factor limiting aerogel-based DSSC performance is light loss due to scattering. Nevertheless, variants of the doubly coaxial structure may prove useful in devising DSSCs that can achieve excellent energy conversion efficiencies even with fast redox shuttles.

Novel 3-nitro-1H-1,2,4-triazole-based aliphatic and aromatic amines as anti-chagasic agents.

A series of novel 2-nitro-1H-imidazole- and 3-nitro-1H-1,2,4-triazole-based aromatic and aliphatic amines were screened for antitrypanosomal activity and mammalian cytotoxicity by the Drugs for Neglected Diseases initiative (DNDi). Out of 42 compounds tested, 18 3-nitro-1,2,4-triazoles and one 2-nitroimidazole displayed significant growth inhibitory properties against T. cruzi amastigotes (IC(50) ranging from 40 nM to 1.97 µM), without concomitant toxicity toward the host cells (L6 cells), having selectivity indices (SI) 44-1320. Most (16) of these active compounds were up to 33.8-fold more potent than the reference drug benznidazole, tested in parallel. Five novel 3-nitro-1,2,4-triazoles were active against bloodstream-form (BSF) T. b. rhodesiense trypomastigotes (IC(50) at nM levels and SI 220-993). An NADH-dependent nitroreductase (TbNTR) plays a role in the antiparasitic activity because BSF T. b. brucei trypomastigotes with elevated TbNTR levels were hypersensitive to tested compounds. Therefore, a novel class of affordable 3-nitro-1,2,4-triazole-based compounds with antitrypanosomal activity has been identified.