Biomedical subjects

Lev A Dykman

Publications and source records attributed to Lev A Dykman.

5 recordsLinked to original sources

PubMed2005

Preparation and optical scattering characterization of gold nanorods and their application to a dot-immunogold assay.

We describe optical monitoring of the synthesis of gold nanorods (NRs) based on seed-mediated growth in the presence of the soft surfactant template cetyltrimethyilammonium bromide. To separate NRs from spheres and surfactants we fractionated samples in the density gradient of glycerol. The optical properties of NRs were characterized by extinction and differential light-scattering spectra (at 90 degrees, 450-800 nm) and by the depolarization light-scattering ratio, I(vh)/I(vv), measured at 90 degrees with a helium-neon laser. Theoretical spectra and the I(vh)/I(vv) ratios were calculated by the T-matrix method as applied to randomly oriented NRs, which were modeled by right-circular cylinders with semispherical ends. The simulated data were fitted to experimental observations by use of particle length and width as adjustable parameters, which were close to the data yielded by transmission electron microscopy. The sensitivity of the long-wavelength resonance of NRs to the dielectric surroundings was examined both experimentally and theoretically by comparison of the extinction spectra of NRs in water and in a 25% glycerol solution. Finally, we discuss the application of NR-protein A conjugates to a dot-immunogold assay with the example of biospecific staining of human IgG molecules adsorbed onto small membrane spots.

Biosensing Techniques↗

PubMed2005

Can the light scattering depolarization ratio of small particles be greater than 1/3?

According to the theory of light scattering by small randomly oriented particles, the depolarized ratio of the scattered intensities, I(vh)/I(vv), cannot exceed 1/3. Here we show that this conclusion does not hold for nonspherical plasmon resonant metal particles. Our analysis is based on the Rayleigh approximation and the exact T-matrix method as applied to spheroids and circular cylinders with semispherical ends. For small particles, the condition I(vh)/I(vv) >1/3 can be satisfied within the upper left quadrant of the complex relative dielectric permeability Real(eps) < -2 (rods) and within the upper unit semicircle centered at Real(eps) = -1 (disks). For gold nanorods with the axis ratio exceeding 2, the maximal theoretical values I(vh)/I(vv) lie between 1/3 and 3/4 at wavelengths of 550-650 nm. The extinction and static light scattering spectra (450-850 nm, at 90 degrees degrees) as well as the depolarized ratio of He-Ne laser light scattering were measured with gold nanospheres (the average diameters of 21, 29, and 46 nm) and nanorods (the longitudinal plasmon resonance peak positions at 655, 692, and 900 nm). The measured depolarization ratios of nanospheres (0.07-0.16) and nanorods (0.3-0.48) are in good agreement with theoretical calculations based on estimations of the average particle size and shape.

Anisotropy↗

PubMed2005

A protein assay based on colloidal gold conjugates with trypsin.

The standard sol particle immunoassay (SPIA) is based on a biospecific aggregation of gold nanoparticle conjugates, followed by conventional spectrophotometry. Here we propose a novel SPIA format that uses microtitration immunological plates and an enzyme-linked immunosorbent assay reader. The novel and standard assays are exemplified by determination of immunoglobulin G by using 15-nm colloidal gold-protein A conjugates. We also describe a novel sol particle-trypsin assay using conjugates of gold nanoparticles with trypsin. The method is based on measuring spectral extinction changes caused by the addition of protein to a conjugate solution. The changes in the extinction spectra are presumed to be related to aggregation of gold nanoparticles caused by polyvalent binding of protein molecules to the trypsin molecules of the conjugates.

Enzyme-Linked Immunosorbent Assay↗

PubMed2004

Studies of Listeria monocytogenes-antibody binding using electro-orientation.

An electro-optical (EO) approach has been used for studies of Listeria monocytogenes-antibody binding. The EO analyzer, which has been developed at the State Research Center for Applied Microbiology, Obolensk, was used as a basic instrument for EO measurements. AC electro-kinetic effects depend on dielectric properties of bioparticles, their composition, morphology, the medium, and the frequency of applied electrical field. Electro-orientational spectra were used for discrimination of bacteria before and after selective binding with antibodies. The measurements were performed using a discrete set of frequencies of the orienting electric field (10, 100, 250, and 500 kHz). During biospecific interactions an antibody is bound to the microorganism causing a change in the dielectric properties of the microorganism-antibody complex and the EO signal reaches its maximum at 100-200 kHz. It has been shown that the biospecific interactions of L. monocytogenes cells with anti-Listeria antibody in the presence of Escherichia coli K-12, and Azospirillum brasilense Sp7 change the EO signals significantly. Thus, the determination of the presence of particular bacteria within a mixed sample may be achieved by selection and matching of antibodies specific to individual bacterium types and by comparing spectra of bacterium in the presence and in the absence of specific antibody.

Antibodies↗

PubMedDate not supplied

Spectroimmunochemistry using colloidal gold bioconjugates.

Using surface-enhanced infrared absorption (SEIRA) spectroscopy of dry films of colloidal gold (CG) bioconjugates with protein A, it is shown that certain characteristic bands of the protein (e.g., amide I, amide II and some other vibration modes) are essentially affected by the metal surface. Thus, the method may be used for controlling the quality of such bioconjugates. Moreover, it is demonstrated that the biospecific reaction of protein A attached to CG particles with human immunoglobulin G (IgG) results in further essential changes in SEIRA spectra, providing a means for an easy and rapid IR spectroscopic detection of biospecific immunochemical interactions (i.e., spectroimmunochemistry). The results obtained can form a basis for developing test systems for detecting various biospecific interactions.

Binding Sites↗