Denys Naumenko

Graphene-enhanced Raman imaging of TiO2 nanoparticles

The interaction of anatase titanium dioxide (TiO(2)) nanoparticles with chemical vapour deposited graphene sheets transferred on glass substrates is investigated by using atomic force microscopy, Raman spectroscopy and imaging. Significant electronic interactions between the nanoparticles of TiO(2) and graphene were found. The changes in the graphene Raman peak positions and intensity ratios indicate that charge transfer between graphene and TiO(2) nanoparticles occurred, increasing the Raman signal of the TiO(2) nanoparticles up to five times. The normalized Raman intensity of TiO(2) nanoparticles per their volume increased with the disorder of the graphene structure. The complementary reason for the observed enhancement is that due to the higher density of states in the defect sites of graphene, a higher electron transfer occurs from the graphene to the anatase TiO(2) nanoparticles.

In vivo characterization of protein uptake by yeast cell envelope: single cell AFM imaging and μ-tip-enhanced Raman scattering study

Direct detection of biological transformations of single living cells in vivo has been performed by the advanced combination of local topographic imaging by Atomic Force Microscopy (AFM) and label-free sub-surface chemical characterization using new μ-Tip-Enhanced Raman Spectroscopy (μ-TERS). The enhancing mechanism for μ-TERS tips with micrometre range radius differs significantly to that of the conventional tapered structures terminated by a sharp apex and conditioned by the effects of propagating instead of localizing surface plasmon resonance phenomena. Sub-wavelength light confinement in the form of a nonradiative evanescent wave near the tip surface with penetration depth in the sub-micrometre range opens the way for monitoring of subsurface processes near or within the cell wall, inaccessible by other methods. The efficiency of the approach has been demonstrated by the analysis of the cell envelope of genetically modified (by glucose dehydrogenase (GDH) gene bearing Kluyveromyces lactis toxin signal sequence) yeast cells enriched by GDH protein. The presence of trans-membrane fragments in GDH together with the tendency to form active dimers and tetramers causes the accumulation of the proteins within the periplasmic space. These results demonstrate that the advanced combination of AFM imaging and subsurface chemical characterization by the novel μ-TERS technique provides a new analytical tool for the investigation of single living cells in vivo.

Generation of diversiform gold nanostructures inspired by honey's components: growth mechanism, characterization, and shape separation by the centrifugation-assisted sedimentation.

The green synthesis of irregular-shaped nanomaterials used for various applications in nanoplasmonics, medicine, and biotechnology creates an economical and environmental challenge. We describe the rapid wet-chemical approach to synthesis of stable and water-soluble gold nanostructues at room temperature. In addition to spherical and road-like nanoparticles, gold decahedra and triangular plates were grown using the one-step synthesis process of HAuCl(4) in the presence of honey, in which main components act as reducing (glucose) and stabilizing (fructose) agents; the mechanism of the process is discussed in details. The requirements for anisotropic phase boundaries for generation of polyhedral gold nanocrystals in solutions are highlighted. The synthesis, morphology, and separation procedure of gold nanoparticles are examined using the techniques of optical spectroscopy, transmission electron microscopy, and atomic force microscopy. We demonstrate that centrifugation can be used for efficient separation of nanoparticles with different shapes from a mixture. It was found that while centrifuging, the spheres sediment at the bottom of the tube, segregating from rods that form a deposit on the side wall, whereas polygons remain in the solution.

Picosecond laser ablation for silicon micro fuel cell fabrication

We have investigated laser ablation as a microfabrication approach to produce micro fuel cells (MFCs) in silicon. Picosecond pulses (15xa0ps) at a wavelength of 355xa0nm are used to make all of the MFC structures. To assess the benefits and drawbacks of laser ablation, reference cells have been produced by deep reactive ion etching (DRIE) using matching geometries. Ablated and etched cells have been evaluated and compared side by side. Our conclusion is that picosecond laser ablation is very well suited for MFC fabrication. The ablated cells match or excel DRIE-microfabricated cells in terms of current and power densities. Ablated MFCs achieved 47.6 mW cm−2xa0of power density and 121xa0mA cm−2xa0current density.

Confocal Raman Spectroscopy of Biological Objects under Conditions of Photoinduced Luminescence Self-Quenching

A study was carried out on the mechanism of luminescence self-quenching of heterogeneous biological objects using laser irradiation at 532 nm (50 μW/ μm2) in the format of a confocal microscope. Laser irradiation was found to reduce the luminescence intensity of material by a factor of 3–5, which permits us to obtain informative Raman scattering spectra of the dried cellular envelope of yeast. For irradiation times less than ~3-5 min, quenching is probably due either to formation of radiationless complexes of the excited chromophore molecules with the environment (excimers and/or exciplexes) or partial photodecomposition. Longer irradiation times lead to thermal degradation of the samples with the appearance of peaks corresponding to amorphous carbon.

Evanescent-field-induced Raman scattering for bio-friendly fingerprinting at sub-cellular dimension

Evanescent field induced chemical imaging concept has been realized in analytical platform based on the µ-tip-enhanced Raman scattering spectroscopy (µ-TERS). The technique aimed to minimize thermal decomposition of dried biological sample as the result of huge concentration of optical field near the tip by increasing the size of an aperture-less excitation source. µ-TERS technique is similar to classical biosensor systems based on propagating surface plasmon resonance phenomenon but with sensitive elements a few micrometers in size that can be targeted to the area of interest. The utility of the concept is exemplified by the analysis of dried single cell envelope of genetically modified Saccharomyces cerevisiae yeast cells, which do not have any heat-removing pathways, by water as in the case of the living cell. Practical excitation conditions effective for µ-TERS Raman observation of single layer dried biological samples without photodamage-related spectral distortion have been determined - the allowable limit is above 30s at 13 µW/µm(2). Finally, potential of µ-TERS spectroscopy as new bio-friendly instrumental platform for chemical fingerprinting and analytical characterization of buried nanoscale features is discussed.

Nanometer-Thick Textured ZnO Films: Preparation, Characterization and Interaction with Ethanol Vapor

A study was carried out on the effect of the reaction temperature in atomic layer deposition on the structural and piezoelectric properties of thin ZnO films (5–50 nm) by scanning electron microscopy, X-ray diffraction, piezoresponse force microscopy, and surface acoustic wave (SAW) spectroscopy. The piezoresponse was shown to be mainly a function of ZnO grain size and the monocrystalline structure perpendicular to the substrate plane. The results demonstrate promise for the use of textured ZnO films as sensitive coatings for acoustic gas sensors in instruments based on the SAW transducer amplification-frequency response.