Biomedical subjects

George Chumanov

Publications and source records attributed to George Chumanov.

8 recordsLinked to original sources

PubMed2006

Monitoring DPA release from a single germinating Bacillus subtilis endospore via surface-enhanced Raman scattering microscopy.

A method for monitoring DPA release from a single germinating Bacillus subtilis endospore is reported. High S/N ratio SERS spectra were obtained with excitation power 3 mW at 647.1 nm and 1 min spectral collection times. The method is proof-of-principle for the SERS detection limit at the single spore level. This represents a 100- to 1000-fold improvement over previously reported detection limits for SERS-based measurements of DPA in endospores.

Bacillus subtilis↗

PubMed2006

Monitoring the kinetics of Bacillus subtilis endospore germination via surface-enhanced Raman scattering spectroscopy.

Mirror sandwich SERS substrates (M3S) were used to monitor the kinetics of Bacillus subtilis endospore germination. The sandwich configuration of the substrates allows real-time observation of germination in samples that contained only several hundred endospores. The enhancement provided by the substrates is attributed to the enhanced local electromagnetic field that originates from coupling between the Ag nanoparticles and the underlying metal film as well as from coupling between the Ag nanoparticles themselves. The germination kinetics at varying concentrations of l-alanine and different temperatures were studied by monitoring the intensity and growth of the Raman peak at 1010 cm(-1), which is characteristic of dipicolinic acid. A total of four concentrations (50, 75, 100, and 150 mM) of l-alanine and three different temperatures (30, 37, and 55 degrees C) were investigated.

Alanine↗

PubMed2005

Nanoparticle-mirror sandwich substrates for surface-enhanced Raman scattering.

Sandwich surface-enhanced Raman scattering (SERS) substrates (3S) utilizing coupling between continuous metal films and plasmonic particles were fabricated using silver mirrors, electrochemically roughened films, and various sizes of silver nanoparticles. The effect of excitation wavelength and nanoparticle size on SERS spectra of poly(vinylpyridine), selected as a model compound, was studied to determine the optimum conditions for the strongest SERS signal. The Raman enhancement resulted from the plasmon coupling of silver nanoparticles to the underlying continuous film as well as the lateral plasmon coupling between the silver nanoparticles. The formation of the charge transfer complex was also observed. The 3S configuration was used to obtain SERS spectra of dipicolinic acid (DPA), a chemical signature for Bacillus anthracis.

Journal Article↗

PubMed2005

Multipole plasmon resonances of submicron silver particles.

Single crystal, silver particles of 215 +/- 10 nm size were synthesized in solution using the hydrogen reduction method and were characterized by UV-visible extinction spectroscopy and electron microscopy. The extinction spectra reveal the presence of higher order multipoles of the plasmon resonance, such as quadrupole, octupole, and hexadecapole, in addition to the dipole. The formation of higher order multipoles was continuously monitored during the particles growth. Mie extinction calculations were performed and are in good agreement with the measured extinction spectra. The frequency shift of all plasmon modes was measured as a function of the refractive index of the surrounding dielectric medium.

Microspheres↗

PubMed2005

Synthesis and optical properties of silver nanoparticles and arrays.

This Minireview systematically examines optical properties of silver nanoparticles as a function of size. Extinction, scattering, and absorption cross-sections and distance dependence of the local electromagnetic field, as well as the quadrupolar coupling of 2D assemblies of such particles are experimentally measured for a wide range of particle sizes. Such measurements were possible because of the development of a novel synthetic method for the size-controlled synthesis of chemically clean, highly crystalline silver nanoparticles of narrow size distribution. The method and its unique advantages are compared to other methods for synthesis of metal nanoparticles. Synthesis and properties of nanocomposite materials using these and other nanoparticles are also described. Important highlights in the history of the field of metal nanoparticles as well as an examination of the basic principles of plasmon resonances are included.

Crystallization↗

PubMed2004

Synthesis and characterization of titania-coated silver nanoparticles.

Silver particles of 70 +/- 10 nm mean diameter were coated with uniform layers of amorphous titania by the hydrolysis and polycondensation process using titanium(IV) n-butoxide in aqueous solution. Because of the large dielectric function of titania, a shift to the longer wavelengths was observed for the plasmon resonance maximum of coated silver nanoparticles. By changing the alkoxide to particles ratio in the reaction mixture, thickness ranging from 5 to 20 nm was obtained. Hydrothermal treatment performed on coated particles at 350 degrees C for 4 h converted amorphous titania to the anatase crystalline form. The anatase form was confirmed by X-ray powder diffraction. More red shift of the plasmon resonance was observed for the hydrothermally treated samples compared with the particles coated with amorphous titania.

Coated Materials, Biocompatible↗

PubMed2003

Light-induced coherent interactions between silver nanoparticles in two-dimensional arrays.

Silver nanoparticles arranged in two-dimensional arrays experience quadrupolar coupling of plasmon resonances when irradiated with visible light. This coupling leads to the formation of the coherent plasmon mode characterized by an intense narrow resonance in the blue spectral range in the extinction spectrum. The coupling and the intensity of this mode can be effectively controlled by varying the distance between particles. The interparticle distance was varied by biaxial stretching of the arrays prepared in transparent elastomeric film of poly(dimethylsiloxane). The observed phenomenon exemplifies a generic approach in which new optical properties of materials can be engineered by organizing metal nanoparticles in various one-, two-, and three-dimensional structures. Further development of this approach will result in the discovery of novel principles of both fundamental and practical importance.

Journal Article↗

PubMed2002

Immobilization of antibodies on glass surfaces through sugar residues.

This work characterizes substrates for immunoassays obtained through the immobilization of vectorially oriented antibodies on glass. The method of preparation is based on the condensation reaction between an aldehyde group on the F(c) portion of antibodies and the hydrazide group on the modified glass surface. Light microscopy and AFM imaging in height and phase modes were used to assess the properties of the modified surface. Both techniques are consistent with a fairly uniform antibody coverage on the micrometer and submicrometer scales. ELISA tests were used to evaluate the activity and surface distribution of immobilized antibodies as well as nonspecific binding to surfaces after various modification steps. It was shown that exposure of the surfaces to a BSA solution minimized nonspecific binding to undetectable levels.

Antibodies↗