SAMs

• Self-assembled monolayer of alkanephosphoric acid on nanotextured Ti
  Authors: Clair S, Variola F, Kondratenko M, Jedrzejowski P 4, Nanci A, Rosei F, Perepichka DF
  JOURNAL OF CHEMICAL PHYSICS 128 (14) 144705 (2008)
  DOI: 10.1063/1.2876421
  Abstract: Surface modification. of titanium and its alloys is of great importance for their practical application as biomedical implants. We have studied and compared assembly of dodecylphosphoric acid on commercial polished and on nanostructured titanium disks. The latter were produced by chemical etching that- created nanoscale pits of typical size of about 20 nm. Enhanced hydrophobicity and high molecular density were obtained after functionalization of the nanotextured substrate. Aging tests showed a lifetime of the organic films of about one month in phosphate buffer. The samples were characterized by means of infrared spectroscopy, contact angle measurements, ellipsometry, and atomic force and scanning tunneling microscopies.
  Email: rosei@emt.inrs.ca, dmitrii.perepichka@mcgill.ca



• Orientation Analysis of omega-Substituted Long-Chain Alkanethiols Self-Assembled on Au Substrate
  Authors: P.N. Angelova, K. Hinrichs, K.V. Kostova, D.T. Tsankov
  JOURNAL OF PHYSICAL CHEMISTRY C 112(45), 17683-17687 (2008)
  Abstract: Monolayers from para-substituted benzyl esters of 16-mercaptohexadecanoic acid (R = -Cl; -OCH3) self-assembled on (111)-textured gold films have been studied in detail with infrared and visible spectroscopic ellipsometry and contact angles measurements. The experimental data testify that these monolayers on gold tend to adopt tilt angles smaller than typical for n-alkanethiols, while the orientation of the phenyl rings is almost perpendicular to the surface. The same precursor molecules self-assembled on silver showed arrangement of the aliphatic chains characteristic for long-chain alkanethiols but differently tilted orientation of the terminal phenyl rings. An attempt was made to explain that different behavior with the different surface energetics of gold and silver substrates
  Email: karsten.hinricbs@isas.de, dtsankov@orgchm.bas.bg



• On the self assembly of short chain alkanedithiols
  Authors: H. Hamoudi, Z. Guo, M. Prato, C. Dablemont, W.Q. Zheng, B Bourguignon, M. Canepa, V.A. Esaulov,
  PHYSICAL CHEMISTRY CHEMICAL PHYSICS 10 (45) 6836-6841 (2008)
  Abstract: A study of the self-assembly of nonane-alkanedithiol monolayers on gold in n-hexane and ethanol solvents is presented. Self-assembled monolayers (SAMs) are characterised by reflection-absorption infrared spectroscopy (RAIRS), sum frequency generation (SFG) and spectroscopic ellipsometry (SE) measurements. Data obtained for alkanethiols SAMs are also shown for comparison. The measurements show that nicely organized HSC9SH SAMs can be obtained in n-hexane provided that N2-degassed solutions are used and all preparation steps are performed in the absence of ambient light. SFG measurements show that these SAMs have free standing SH groups. Use of an un-degassed and/or light-exposed n-hexane solutions leads to a worse layer organization. Preparation in ethanol, even in degassed solutions with processing in the dark, leads to poorly organized layers and no sign of free-SH groups was observed.
  Email: vladimir.esaulov@u-psud.fr



• Properties of octadecanethiol self-assembled monolayers deposited on GaAs from liquid and vapor phases
  Authors: H.A. Budz, R.R. LaPierre
  JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 26 (6) 1425-1431 (2008)
  Abstract: Octadecanethiol (ODT), CH3(CH2)(17)SH, self-assembled monolayers (SAMs) were deposited on GaAs (100) substrates from solution and from vapor phase. The monolayers assembled from solution were prepared by incubating the substrate in a dilute millimolar ODT/ethanol solution, while vapor-deposited monolayers were prepared from vapor phase transport of ODT in an ultrahigh vacuum environment. The structural and optical characteristics of the resulting SAMs were examined with contact angle (CA) analysis, photoluminescence (PL) spectroscopy, atomic force microscopy (AFM), and spectroscopic ellipsometry. Static CA measurements of the SAMs indicated the successful formation of highly organized monolayers by both preparation routes. In contrast, PL spectroscopy, AFM, and ellipsometry measurements showed differences in the optical and structural properties of SAMs prepared from liquid and vapor phases. The data obtained indicate that more densely packed monolayers exhibiting greater surface coverage and therefore, increased passivation characteristics are assembled from vapor phase.
  Email: lapierr@mcmaster.ca
  
  
• In-situ and real-time protein adsorption study by Spectroscopic Ellipsometry
  Authors: S. Lousinian, S. Logothetidis
  THIN SOLID FILMS 516 (22) 8002-8008 (2008)
  Abstract: Protein adsorption is an important aspect for the improvement of many applications, such as medical implants, biosensor design, etc. The density, orientation and conformation of surface-bound proteins are believed to be key factors in controlling subsequent cellular adhesion. The aim of this work is the development of a methodology in order to study in-situ and real-time protein adsorption phenomenon, and describe fibrinogen adsorption on amorphous hydrogenated carbon (a-C:H) thin films developed by rf reactive magnetron sputtering under different deposition conditions. Spectroscopic Ellipsometry (SE) in Vis-UV energy region was implemented for this purpose. SE is a non-destructive, surface sensitive technique, with the capability of performing real-time measurements in air as well as in liquid environment, with great potential in biomedical studies. An appropriate ellipsometric model has been developed, in order to describe accurately the protein adsorption mechanisms in real-time. It was found that the thickness and density of fibrinogen are larger on the a-C:H thin film deposited under absence of bias voltage application. The differences in fibrinogen thickness and transition of fibrinogen from liquid to adsorbed state are presented and discussed in the terms of the Surface and optical properties of a-C:H films.
  
  
• Dynamic protein adsorption at the polyurethane copolymer/water interface
  Authors: Yaseen M, Salacinski HJ, Seifalian AM, Lu JR
  BIOMEDICAL MATERIALS 3 (3) 034123 (2008)
  DOI: 10.1088/1748-6041/3/3/034123
  Abstract: Polyurethanes (PU) and their polymeric derivatives are widely used in the manufacturing of medical devices. It is important to understand how protein adsorbs onto PU materials as this molecular process directly implicates surface biocompatibility. In this work, we compared protein adsorption at the PU film surfaces with that from the hydrophilic silicon oxide. Two PU polymers were used, a commercial polyurethane (PUA) and a novel poly(carbonate-urea) urethane matrix containing silsesquioxanes (PU4). AFM imaging revealed micro-domain segregation on both PU surfaces, but the incorporation of pendent silsesquioxanes made the PU4 surface much rougher, with the outer surface comprised of soft upper PU segments and lower PU-silsesquioxane hard segments. It appeared that fibrinogen was preferable to adsorb onto the upper soft PU segments. The spectroscopic ellipsometry (SE) measurements at the PU film/solution interface showed that human serum albumin (HSA) adsorption was little affected by surface chemistry whilst fibrinogen adsorption was much greater on the two PU surfaces indicating a strong surface effect. Further studies revealed that HSA adsorption was reversible on hydrophilic SiO2 against changes in pH from 5 to 7, but irreversible on the two PU surfaces. In contrast, fibrinogen adsorption against the same pH cycling was found to be irreversible on all three surfaces. The different extent of irreversibility was clearly indicative of different interfacial interactions. Sequential protein adsorption revealed that the PU4 surface shared similar physiochemical properties to the SiO2 surface, demonstrating the success in incorporating the siloxane pendant nanocages. The knowledge of protein surface structure and behaviour may lead to the development of effective means to control surface biocompatibility.
  
  
• Plasmon microscopy and imaging ellipsometry of Artrobacter oxydans attached on polymer films
  Authors: Marinkova D, Bivolarska M, Ahtapodov L, Yotova L, Mateva R, Velinov T
  COLLOIDS AND SURFACES B-BIOINTERFACES 65 (2) 276-280 (2008)
  DOI: 10.1016/j.colsurfb.2008.04.014
  Abstract: The attachment of Artrobacter oxydans 1388 on a newly synthesized biodegradable copolymer of poly(hexanlactam)-co-block-poly-(delta-valerolactone) is investigated by optical, microscopic and biochemical methods. The potentials of surface plasmon microscopy and imaging ellipsometry for detecting microorganisms when Al films are used to excite plasmons is assessed by comparing images obtained by these methods with dark field microscopy pictures. The experimental results demonstrate that in this case imaging ellipsometry and plasmon microscopy in transmission are promising methods and can be used in optical sensors for monitoring cell adhesion.
  
  
• Dynamic adsorption of monoclonal antibody layers on hydrophilic silica surface: A combined study by spectroscopic ellipsometry and AFM
  Authors: Wang XQ, Wang YN, Xu H, Shan HH, Lub JR
  JOURNAL OF COLLOID AND INTERFACE SCIENCE 323 (1) 18-25 (2008)
  DOI: 10.1016/j.jcis.2008.04.024
  Abstract: Spectroscopic ellipsometry (SE) and atomic force microscopy (AFM) have been used to investigate the adsorption of a mouse monoclonal antibody (type IgG1, anti-beta-ICG) on hydrophilic silica (bearing weak negative charges above pH 3), followed by the assessment of binding of human chorionic gonaclotrophin (hCG). The antibody is a relatively large molecule with a molecular weight of 150 kDa and the isoelectric point (IP) around pH 6. The antibody adsorption was conducted at pH 4.0, 6.0 and 8.0 to examine the role of charge interaction. Ellipsometric results show that away from the IP, both initial adsorption rate and surface excess decreased, with the reduction at pH 8.0 being more pronounced than that at pH 4.0 due to the electrostatic repulsion not only between the charged antibody molecules within the adsorbed layer but also between antibody and the silica surface. Whilst parallel AFM measurements confirmed the main trend of pH dependent antibody adsorption, they also revealed the tendency of surface aggregation with increasing surface coverage. AFM height profiling at low surface coverage confirmed the "flat-on" orientation of adsorbed antibody molecules, consistent with the previous study by neutron reflection. Interestingly, the antibody height at pH 4.0 was found to be lower than that at pH 8.0, showing the influence from different electrostatic interactions under the two pH conditions. Subsequent hCG binding to the adsorbed antibodies was found to decrease with increasing surface coverage due to the steric hindrance. Under similar antibody surface coverage, the hCG binding ratio at pH 8 was higher than that at pH 4,0, a difference that could only be accounted for by the tighter surface confinement at pH 4.0