Saim Emin

Nanostructured semiconductors for efficient water splitting

Photoelectrochemical (PEC) water splitting, in which molecular hydrogen and oxygen are directly dissociated from water molecules using semiconductor electrodes, dates back to 1972.1 Certain factors have, however, delayed developments in this field over the last few decades. Limitations include the expense of the required materials, electrode instability against photocorrosion, and poor solar-to-hydrogen (STH) generation efficiencies.2 Recent advances in the field of nanotechnology may enable these bottlenecks to be overcome. PEC watersplitting research currently targets low-cost and Earth-abundant elements that show promising STH conversion efficiencies. The semiconductor materials used usually include inexpensive metal oxides, metal sulfides, and metal carbides. A stateof-the-art device based on tungsten-doped bismuth vanadate photoanodes3 has enabled an STH conversion efficiency of 5%. The highest efficiency to date (14%) was achieved using a titanium dioxide-coated indium phosphide photocathode.4 These recent studies show the potential for commercial PEC water-splitting devices. Surface roughness plays a vital role in improving the collection of photogenerated carriers at the semiconductor-electrolyte interface (see Figure 1).5 The water oxidation reaction at a semiconductor electrode is much more efficient if a rough surface is used instead of a smooth one. This is due to its higher surface area, which leads to more photocatalytic sites and thus to higher activity. Structures such as nanorods, nanotubes, nanoplates, and porous films can be used to introduce surface roughness in electrodes. We have developed a novel approach for the preparation of nanostructured porous tungsten trioxide (WO3) thin films.6 These textured films—see Figure 2—are composed of small individual nanoparticles and show high surface area and porosity. The films exhibit catalytic activity upon illumination with Figure 1. Minority diffusion lengths for the electron (Le , –) and hole (Lh, +) on flat and rough electrode surfaces. On the textured electrode, the distance between the surface and the location at which holes (+) are generated can be shorter in comparison with the flat semiconductor substrate.

Immobilization and stretching of 5'-pyrene-terminated DNA on carbon film deposited on electron microscope grid.

The immobilization and stretching of randomly coiled DNA molecules on hydrophobic carbon film is a challenging microscopic technique, which possess various applications, especially for genome sequencing. In this report the pyrenyl nucleus is used as an anchor moiety to acquire higher affinity of double stranded DNA to the graphite surface. DNA and pyrene are joined through a linker composed of four aliphatic methylene groups. For the preparation of pyrene‐terminated DNA a multifunctional phosphoramidite monomer compound was designed. It contains pyrenylbutoxy group as an anchor moiety for π‐stacking attachment to the carbon film, 2‐cyanoethyloxy, and diisopropylamino as coupling groups for conjugation to activated oligonucleotide chain or DNA molecule. This monomer derivative was suitable for incorporation into automated solid‐phase DNA synthesis and was attached to the 5′ terminus of the DNA chain through a phosphodiester linkage. The successful immobilization and stretching of pyrene‐terminated DNA was demonstrated by conventional 100 kV transmission electron microscope. The microscopic analysis confirmed the stretched shape of the negatively charged nucleic acid pieces on the hydrophobic carbon film. Microsc. Res. Tech. 78:994–1000, 2015.

Biotinylated vanadium and chromium sulfide nanoparticles as probes for colocalization of membrane proteins

We report the microemulsion synthesis of vanadium and chromium sulfide nanoparticles (NPs) and their biological application as nanoprobes for colocalization of membrane proteins. Spherical V2S3 and Cr2S3 NPs were prepared in reverse microemulsion droplets, as nanoreactors, obtained by the surfactant sodium bis(2‐ethylhexyl) sulfosuccinate (AOT) in nonpolar organic phase (heptane). Electron microscopic data indicated that the size distribution of the nanoparticles was uniform with an average diameter between 3 ÷ 5 nm. The prepared hydrophobic nanocrystals were transferred in aqueous phase by surface cap exchange of AOT with biotin‐dihydrolipoic ligands. This substitution allows the nanoparticles solubility in aqueous solutions and confer their bioactivity. In addition, we report the conjugation procedure between α‐Lipoic acid (LA) and biotin (abbreviated as biotin‐LA). The biotin‐LA structure was characterized by 1D and 2D NMR spectroscopy. The biotinylated vanadium and chromium sulfide nanoparticles were tested as probes for colocalization of glutamate receptors on sodium‐dodecyl‐sulfate‐digested replica prepared from rat hippocampus. The method suggests their high labeling efficiency for study of membrane biological macromolecules. Microsc. Res. Tech. 79:799–805, 2016.

Electron Microscopic Visualization of Complementary Labeled DNA With Platinum-Containing Guanine Derivative

The object of the present report is to provide a method for a visualization of DNA in TEM by complementary labeling of cytosine with guanine derivative, which contains platinum as contrast‐enhanced heavy element. The stretched single‐chain DNA was obtained by modifying double‐stranded DNA. The labeling method comprises the following steps: (i) stretching and adsorption of DNA on the support film of an electron microscope grid (the hydrophobic carbon film holding negative charged DNA); (ii) complementary labeling of the cytosine bases from the stretched single‐stranded DNA pieces on the support film with platinum containing guanine derivative to form base‐specific hydrogen bond; and (iii) producing a magnified image of the base‐specific labeled DNA. Stretched single‐stranded DNA on a support film is obtained by a rapid elongation of DNA pieces on the surface between air and aqueous buffer solution. The attached platinum‐containing guanine derivative serves as a high‐dense marker and it can be discriminated from the surrounding background of support carbon film and visualized by use of conventional TEM observation at 100 kV accelerated voltage. This method allows examination of specific nucleic macromolecules through atom‐by‐atom analysis and it is promising way toward future DNA‐sequencing or molecular diagnostics of nucleic acids by electron microscopic observation. Microsc. Res. Tech. 79:280–284, 2016.