Mikhail S. Kotelev

Spectroscopy of Scattered Light for the Characterization of Micro and Nanoscale Objects in Biology and Medicine

The biomedical uses for the spectroscopy of scattered light by micro and nanoscale objects can broadly be classified into two areas. The first, often called light scattering spectroscopy (LSS), deals with light scattered by dielectric particles, such as cellular and sub-cellular organelles, and is employed to measure their size or other physical characteristics. Examples include the use of LSS to measure the size distributions of nuclei or mitochondria. The native contrast that is achieved with LSS can serve as a non-invasive diagnostic and scientific tool. The other area for the use of the spectroscopy of scattered light in biology and medicine involves using conducting metal nanoparticles to obtain either contrast or electric field enhancement through the effect of the surface plasmon resonance (SPR). Gold and silver metal nanoparticles are non-toxic, they do not photobleach, are relatively inexpensive, are wavelength-tunable, and can be labeled with antibodies. This makes them very promising candidates for spectrally encoded molecular imaging. Metal nanoparticles can also serve as electric field enhancers of Raman signals. Surface enhanced Raman spectroscopy (SERS) is a powerful method for detecting and identifying molecules down to single molecule concentrations. In this review, we will concentrate on the common physical principles, which allow one to understand these apparently different areas using similar physical and mathematical approaches. We will also describe the major advancements in each of these areas, as well as some of the exciting recent developments.

Rapid optimization of metal nanoparticle surface modification with high-throughput gel electrophoresis.

The ability to effectively control and optimize surface modification of metal nanoparticles is paramount to the ability to employ metal nanoparticles as diagnostic and therapeutic agents in biology and medicine. Here we present a high-throughput two-dimensional-grid gel electrophoresis cell (2D-GEC)-based method, capable of optimizing the surface modification of as many as 96 samples of metal nanoparticles in approximately 1 h. The 2D-GEC method determines not only the average zeta-potential of the modified particles but also the homogeneity of the surface modification by measuring the distance between the front of the sample track and the area where the maximum optical density is achieved. The method was tested for optimizing pH and concentration of the modifiers (pM) for functionalizing gold nanorod thiol-containing acidic agents.

Natranaerobaculum magadiense gen. nov., sp. nov., an anaerobic, alkalithermophilic bacterium from soda lake sediment.

An obligately alkaliphilic, anaerobic, thermo- and halotolerant, spore-forming bacterium was isolated from sediments of soda lake Magadi (Kenya) and designated strain Z-1001(T). Cells of strain Z-1001(T) were straight, Gram-positive rods, slowly motile. Strain Z-1001(T) was found to be an obligate anaerobe. It grew within a pH range from 7.5 to 10.7 with an optimum at 9.25-9.5 (at 40 °C), a temperature range from 20 to 57 °C with an optimum at 45-50 °C, and a NaCl concentration range from 0 to 1.55 M with an optimum at 1.2-1.4 M. Peptides, such as meat and yeast extracts, peptone and tryptone, were fermented by Z-1001(T). Carbohydrates did not support growth. With yeast extract as an electron donor, strain Z-1001(T) reduced S(2)O(3)(2-), NO(-)(3), AsO(3-)(4), Fe(III) citrate and anthraquinone-2,6-disulfonate (AQDS) as electron acceptors. The isolate was able to grow oligotrophically with a very small amount of yeast extract: 0.03 g l(-1). The main fatty acids were C16 : 0, C16 : 1ω7c, C18 : 0 and C18 : 1ω9. The DNA G+C content of the isolate was 35.6 mol%. 16S rRNA gene sequence analysis showed that strain Z-1001(T) is a member of family Natranaerobiaceae, clustering with the type strain of Natranaerobius thermophilus (95.8-96.0 % sequence similarity). On the basis of physiological and phylogenetic data it is proposed that strain Z-1001(T) ( = DSM 24923(T) = VKM B-2666(T)) represents a novel genus and species, Natranaerobaculum magadiense gen. nov., sp. nov.

Ultrashort laser pulse-induced anti-Stokes photoluminescence of hot electrons in gold nanorods

We report observing anti-Stokes broadband radiation induced in gold nanorods by ultrashort laser pulses. The radiation is in the visible spectral range along with the second harmonic peak. Unlike conventional photoluminescence of metal nanoparticles, the energy of the excitation photons is smaller than the gap between the top of the d band and the Fermi level. Because the gold nanorods are irradiated with a pulse whose time is shorter than the electron–phonon equilibration time in gold, the energy is absorbed by s/p band electrons, creating a temperature difference between the electrons and the lattice, as described by the two-temperature model. Therefore, we identify the origin of the observed radiation as the recombination of hot conduction electrons with the d band holes created by the same ultrashort laser pulse.

Nanoparticles Formed onto/into Halloysite Clay Tubules: Architectural Synthesis and Applications

Nanoparticles, being objects with high surface area are prone to agglomeration. Immobilization onto solid supports is a promising method to increase their stability and it allows for scalable industrial applications, such as metal nanoparticles adsorbed to mesoporous ceramic carriers. Tubular nanoclay - halloysite - can be an efficient solid support, enabling the fast and practical architectural (inside / outside) synthesis of stable metal nanoparticles. The obtained halloysite-nanoparticle composites can be employed as advanced catalysts, ion-conducting membrane modifiers, inorganic pigments, and optical markers for biomedical studies. Here, we discuss the possibilities to synthesize halloysite decorated with metal, metal chalcogenide, and carbon nanoparticles, and to use these materials in various fields, especially in catalysis and petroleum refinery.

Synthesis of large uniform gold and core–shell gold–silver nanoparticles: Effect of temperature control

The temperatures of nucleation and growth for gold and silver nanoparticles are quite close to each other in citrate-based seeded-growth synthesis. Hence, thorough temperature control during the synthesis of gold and gold–silver core–shell nanoparticles is expected to improve the yield of uniform non-aggregated nanoparticles suitable for selective contrasting of surface defects. Gold and gold–silver core–shell nanoparticles of size ranging from 20 to 160 nm were synthesized using various means of temperature control. The synthesized nanoparticles were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS) and UV–Vis spectroscopy. Model nanocracks were milled on pipeline steel specimen by focused ion beam (FIB). It was found that to produce large uniform core–shell nanoparticles, thorough temperature control is required during formation of the gold seeds and the silver shell. Moreover, the synthesized nanoparticles were used for selective contrasting of defects on metal surface.

Fluorescence and Cytotoxicity of Cadmium Sulfide Quantum Dots Stabilized on Clay Nanotubes

Quantum dots (QD) are widely used for cellular labeling due to enhanced brightness, resistance to photobleaching, and multicolor light emissions. CdS and CdxZn1−xS nanoparticles with sizes of 6–8 nm were synthesized via a ligand assisted technique inside and outside of 50 nm diameter halloysite clay nanotubes (QD were immobilized on the tube’s surface). The halloysite–QD composites were tested by labeling human skin fibroblasts and prostate cancer cells. In human cell cultures, halloysite–QD systems were internalized by living cells, and demonstrated intense and stable fluorescence combined with pronounced nanotube light scattering. The best signal stability was observed for QD that were synthesized externally on the amino-grafted halloysite. The best cell viability was observed for CdxZn1−xS QD immobilized onto the azine-grafted halloysite. The possibility to use QD clay nanotube core-shell nanoarchitectures for the intracellular labeling was demonstrated. A pronounced scattering and fluorescence by halloysite–QD systems allows for their promising usage as markers for biomedical applications.

Synthesis of bimetallic gold/silver nanoparticles via in situ seeding

A way of synthesizing bimetallic gold/silver nanoparticles with in situ seeding initiated by the addition of sodium borohydride is proposed. The obtained nanoparticles are studied by means of transmission electron microscopy (TEM). Changes in the optical density spectra of the nanoparticles during their coagulation are investigated. The technique allows the rapid acquisition of nontoxic SERS-active nanoparticles with maximum SERS enhancement factor about 105 in the near infrared range for Raman shifts typical for biological objects such as bacterial cells and spores.

Antiknock Properties of Blends of 2-Methylfuran and 2,5-Dimethylfuran with Reference Fuel

The antiknock properties of blends of 2-methylfuran and 2,5-dimethylfuran with a reference fuel containing toluene are studied. The octane numbers of blends of these substances in various concentrations and the change in sensitivity of the fuel are calculated. In the research method it is shown that the octane number of the blend reaches a maximum at an additive concentration of 10 vol. %, while the sensitivity of the fuel increases to a smaller degree when 2-methylfuran is used.

PHOTOBIOREACTOR OPERATION CONDITION OPTIMIZATION FOR HIGH-ENERGY CYANOBACTERIAL BIOMASS SYNTHESIS TO PRODUCE THIRD-GENERATION BIOFUELS

The distinctive features of cultivation of two strains of thermophilic cyanobacteria, Mastigocladus laminosus and Anabaena variabilis, in a pouring-off-filling-up type of photobioreactor are investigated. The dependence of the biomass growth rate and concentration doubling time on the carbon dioxide content in the injected air is studied and the culture medium composition is optimized. It is shown that tap water added with macro- and microelements, instead of analogous distilled water based nutrient medium, facilitates faster biomass growth. The minimum biomass doubling time is 0.9 day for Mastigocladus laminosus and 1.1 days for Anabaena variabilis when the carbon dioxide content in the injected air is 4 vol. %.