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A "polarization mapping" method has been applied to improve the fitting quality of sum frequency generation (SFG) vibrational spectra of complicated systems and validate the data analysis of simple SFG spectra. Using such a method, two-dimensional SFG spectra can be constructed, from which more reliable spectral information can be obtained from a surface/interface. Model calculations as well as experiments have been employed to illustrate the power of the polarization mapping method for spectral analysis of SFG spectra. By using a deuterated polystyrene surface and interfacial protein molecules as examples, we demonstrate that this method is especially important for complicated molecules, such as polymers and proteins. [ABSTRACT FROM AUTHOR]

This study characterizes the molecular surface structures of polyurethane (PU) and plasticized PU films in air, in water, and in albumin solution in situ using a nonlinear optical technique, sum frequency generation (SFG) vibrational spectroscopy. Two different plasticizers are investigated: dioctyl sebacate (DOS) and o-nitrophenyl octyl ether (NPOE). Plasticization of PU is common for biosensors to achieve better adhesion, malleability, elasticity, and permeability; however, this can adversely affect biocompatibility. Our research indicates that plasticizers can segregate to the PU surface not only in air but also in water. In addition, plasticizer content can affect protein adsorption behaviors of PU surfaces. This is the first lime surface-sensitive SFG has been applied to deduce plasticizer surface behavior in situ. More specifically, we found that DOS dominates the surface of the film with DOS surface concentrations higher than DOS bulk concentrations both in air and in contact with an aqueous environment NPOE has a reduced effect at the surface compared to DOS in both air and aqueous environments. Addition of either DOS or NPOE to PU was also found to cause a change in albumin adsorption. [ABSTRACT FROM AUTHOR]