Surface enhanced IR absorption of nucleic acids from tumor cells: FTIR reflectance study.

The data on surface enhanced IR absorption (SEIRA) of nucleic acids deposited on a metal substrate were obtained using FTIR in reflectance mode. A 200-400 A thick gold film on a glass plate was the metal substrate. The approximate enhancement factors of the SEIRA for different vibrations of nucleic acids in our experimental conditions were 3-5. The roughness of the Au surface was about 50 A. Application of this method to nucleic acids isolated from tumor cells revealed some possible peculiarities of their structural organization, namely, the appearance of unusual sugar and base conformations, modification of the phosphate backbone, redistribution of the H-bond net, and so forth. This method enhanced a set of the bands, which is impossible to observe in conventional IR geometry. The SEIRA spectra of the RNA from tumor cells showed more sensitivity to the grade of tumor malignancy than the spectra of the DNA. After application of the anticancer drug doxorubicin to sensitive and resistant strains, the DNA isolated from these strains had different spectral features, especially in the region of the phosphate I and II bands. As induced by anticancer drugs, the conformational changes in the DNA from resistant and sensitive cancer strains could be characterized with different levels of structure disordering.

Analysis of the response of planar polarization interferometer to molecular layer formation: fibrinogen adsorption on silicon nitride surface.

The most sensitive optical method of interferometry was exploited for determination of changes in the refractive index following the adsorption of biological molecules onto the solid surface. Instead of having two waveguiding arms (the main and the reference) in traditional Mach-Zhender interferometer, two ortogonal TM and TE modes propagating through the SiO(2)-Si(3)N(4)-SiO(2) waveguide structure were employed in planar polarization interferometer (PPI). Multiperiodic PPI response was, therefore, formed due to the phase shift between TM and TE modes. A matrix simulation procedure was developed in order to investigate the influence of both the refractive index and molecular layer thickness on the PPI response. Nonspecifical binding of fibrinogen to silicon nitride surface was studied as a model object for PPI testing. The results obtained are in good agreement with the known information about fibrinogen adsorption on the different surfaces. An attempt to introduce the concept of 'surface molecular concentration and molecular polariziability' instead of 'molecular layer thickness and refractivity' was undertaken.

Elastic laser light scattering by GaAs surfaces.

Angle-resolved scattering (ARS) intensities were measured in the backscattering hemisphere for the (1 0 0) and (1 1 1) faces of GaAs single crystals. Three epitaxial layers were deposited onto the GaAs (1 0 0) single-crystalline wafers. The laser elastic light scattering shows the presence of a regular surface microrelief whose orientation corresponds to the crystallographic axes in the surface plane. We studied the statistical properties of this microrelief and determined the parameters that characterize the surface. We propose to use the ARS ratio for two wavelengths (in our case, 632.8 and 441.6 nm) to determine the topographical properties of scattering and to study crystal surface defects.

Atomic structure display of a real silicon surface under light scattering.

Angular dependencies of the scattered light intensity were measured on Si wafers that have different crystallographic orientations by using a He-Ne laser (λ = 632.8 nm, 80 µm spot diameter). During the experiment the Si wafer was fixed relative to the incident beam. Regular patterns were found in the azimuthal-angle-resolved scattering curves. Such patterns seem to be caused by the faceted shallow atomic structures of the surface.