Optical waveguide lightmode spectroscopy

The most recently introduced optical teclmique is based on the retardation of light guided in an optical waveguide when biomolecules of a polarizability different from that of the solvent they displace are adsorbed at the waveguide surface (optical waveguide lightmode spectroscopy, OWLS) [H]. It is even more sensitive than ellipsometry, and the mode... 

Hook F, Vords J, Rodahl M, Kurrat R, Bdni P, Ramsden JJ, Textor M, Spencer ND, Tengvall P, Gold J, Kasemo B (2002) A comparative study of protein adsorption on titanium oxide surfaces using in situ ellipsometry, optical waveguide lightmode spectroscopy, and quartz crystal microbalance/dissipation. Colloids Surf B Biointerfaces 24 155-170... 

M. A. Brusatori, P. R. Van Tassel, Biosensing Under an Applied Voltage Using Optical Waveguide Lightmode Spectroscopy, 5ioieniora and Bioelectronics 18, 1269-1277 (2003). 

The present study aims to understand the influence of solvent quality on the molecular-level friction mechanism of tethered, brushlike polymers. It involves complementary adsorption studies of PLL-,g-PEG by means of optical waveguide lightmode spectroscopy (OWLS) and quartz crystal microbalance with dissipation (QCM-D) as well as friction studies performed on the nanoscale using colloidal-probe lateral force microscopy (LFM). The adsorbed mass measured by QGM-D includes a contribution from solvent molecules absorbed within the surface-bound polymer fllm. This is in contrast to optical techniques, such as OWLS, which are sensitive only to the dry mass of a polymer adsorbed onto the surface of the waveguide.By subtracting the dry mass , derived from OWLS measurements, from the wet mass , derived from QCM-D measurements, it is therefore possible to determine the mass of the solvent per unit substrate area absorbed in the brushlike structure of PLL- -PEG, expressed as areal solvation, P. Areal solvation was varied by choosing solvents (aqueous buffer solution, methanol, ethanol, and 2-propanol) of different quality with respect to the PEG brush. The solvents were characterized in terms of the three-component Hansen solubility parameters, and these values were compared with measured areal solvation of the PEG brush. 

Kurrat R, Textor M, Ramsden JJ, Boni P, Spencer ND. Instrumental improvements in optical waveguide lightmode spectroscopy for the study of biomolecule adsorption. Rev Sci Instrum 1997 68 2172-6. 

The instantaneous reduction of fi upon injection of PLL-g-PEG solution into the tribometer is ascribed to the fast adsorption kinetics of PLL-g-PEG onto oxide surfaces at neutral pH. Previous optical waveguide lightmode spectroscopy (OWLS) studies have already revealed that the adsorption of PLL-g-PEG onto oxide surfaces, including SiO, [6, 10] and iron oxide [6], which comprise the tribopair of this work, starts to occur within seconds, upon exposure of an oxide substrate to the polymer solution, and is virtually completed within a few minutes. However, fast adsorption of PLL-g-PEG is feasible only when the concentration of the polymer solution is sufficiently high, e.g. > 0.1 mg/ml. In fact, in the low-concentration regime, the lubricating capabihties... 

Figure 3. Adsorption behaviour of the three aqueous lubricant additives, sodium dodecylsulphate (SDS), poly(ethylene oxide)-ZtZocjfe-poly(propylene oxide)-bZocl -poly(ethylene oxide) and poly(L-lysine)-grq -poly(ethylene glycol) (PLL-g-PEG), onto poly(dimethylsiloxane) surface from aqueous solution (pH 7.0), as determined by means of optical waveguide lightmode spectroscopy.

Optical waveguide lightmode spectroscopy (OWLS) was used to characterize the adsorption properties of the polymers. Experiments were performed using an OWLS 110 instrument (Microvacuum, Budapest, Hungary). 

Polymer and protein adsorption was studied quantitatively with an optical waveguide sensing technique, optical waveguide lightmode spectroscopy (OWLS). ... 

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