Biomedical subjects

Vitalii Silin

Publications and source records attributed to Vitalii Silin.

3 recordsLinked to original sources

PubMed2004

Control of protein adsorption: molecular level structural and spatial variables.

The adsorption of fibrinogen (Fb) and bovine serum albumin onto polycrystalline Au coated with HS(CH2)3O(CH2CH2O)5CH3 was determined by surface plasmon resonance from bare Au (0% coverage) to the complete ( approximately 100% coverage) self-assembled monolayer (SAM). Both proteins exhibit similar adsorption curves with common onset ( approximately 60% coverage) and range ( approximately 60% to 80% coverage) of minimal protein adsorption. Reflection-absorption infrared spectroscopic data show that widespread order is not present in the films over this range of coverage, indicating loosely packed, bound oligomers that are uniformly distributed and fully screen the underlying substrate. On the basis of our data, we propose a mechanism of protein rejection by oligo(ethylene oxide) (OEO)-modified surfaces in terms of changes in free energy (DeltaGsystem; system = protein + surface) due to oligomer conformational constriction over an area greater than the contact area. Minimal protein adsorption corresponds to the maximum DeltaGsystem for a given compression. This controlled study of protein adsorption provides insights into the molecular level understanding of protein adsorption unavailable from previous polymer and comparative SAM studies.

Adsorption↗

PubMed2004

Isostructural self-assembled monolayers. 2. Methyl 1-(3-mercaptopropyl)-oligo(ethylene oxide)s.

The structural order and ordering conditions of the self-assembled monolayers (SAMs) of HSCH2CH2CH2O(EO)xCH3, where EO = CH2CH2O and x = 3-9, on polycrystalline gold (Au) were determined by reflection-absorption infrared spectroscopy (RAIRS), spectroscopic ellipsometry (SE), and electrochemical impedance spectroscopy. For x = 5-7, RAIRS and SE data show that the oligo(ethylene oxide) [OEO] segments adopt the near single phase, 7/2 helical conformation of the folded-chain crystal polymorph of crystalline poly(ethylene oxide), oriented normal to the substrate. These SAMs exhibit OEO segment structure and orientation identical to that found in a previous isostructural series [HS(CH2CH2O)6-8C18H37 SAMs. Vanderah, D. J., et al. Langmuir 2003, 19, 3752] and are anisotropic films for surface science metrology where structure is constant and thickness increases in 0.30 nm increments. In addition, this is the first example of OEO SAMs to attain this highly ordered, helical conformation where the (EO)x segment is separated from the Au-sulfur headgroup by a polymethylene chain. For x = 4, 8, and 9, the SAMs are largely helical but show evidence of nonhelical conformations and establish the upper and lower limits of the isostructural set. For x = 3, the SAMs are largely disordered containing some all-trans conformation. SAM order as a function of immersion time from 100% water and 95% ethanol indicates that the HSCH2CH2CH2O(EO)5-7CH3 SAMs order faster and under a wider range of conditions than omega-alkyl 1-thiaolio(ethylene oxide) [HS(EO)xCH3] SAMs, reported earlier (Vanderah, D. J., et al. Langmuir 2002, 18, 4674 and Vanderah, D. J., et al. Langmuir 2003, 19, 2612).

Journal Article↗

PubMed2004

Surface-plasmon-resonance-enhanced cavity ring-down detection.

The cavity ring-down technique is used to probe the absolute optical response of the localized surface plasmon resonance (SPR) of a gold nanoparticle distribution to adsorption of trichloroethylene (TCE) and perchloroethylene (PCE) from the gas phase. Extended Mie theory for a coated sphere with a particle-size-dependent dielectric function is used to elucidate size-dispersion effects, the size-dependence of the SPR sensitivity to adsorption, and the kinetics of adsorption. An approximate Gaussian distribution of nanospheres with a mean diameter of 4.5 nm and a standard deviation of 1.1 nm, as determined by atomic force microscopy, is provided by the intrinsic granularity of an ultrathin, gold film, having a nominal thickness of approximately 0.18 nm. The cavity ring-down measurements employ a linear resonator with an intracavity flow cell, which is formed by a pair of ultrasmooth, fused-silica optical flats at Brewster's angle, where the Au film is present on a single flat. The total system intrinsic loss is dominated by the film extinction, while the angled flats alone contribute only approximately 5 x 10(-5)/flat to the total loss. Based on a relative ring-down time precision of 0.1% for ensembles averages of 25 laser shots from a pulsed optical parametric oscillator, the minimum detectable concentrations of PCE and TCE obtained by probing the SPR response are found to be 2 and 7 x 10(-8) mol/L, respectively, based on a 30 s integration time.

Journal Article↗