In Situ Infrared Spectroscopic Monitoring and Characterization of the Growth of Polydopamine (PDA) Films

Modern infrared (IR) spectroscopic methods as in situ IR spectroscopic ellipsometry (in situ IRSE) and the photothermal atomic force microscopy (AFM)-IR technique are introduced as novel analysis methods for characterization of polydopamine (PDA) films. The visible (VIS) and IR ellipsometric studies serve for determination of thicknesses, IR optical constants and discussion of specific vibrational bands. The in situ IR ellipsometric studies (IRSE) of the thin film growth of polydopamine (PDA), a versatile material for bioactive surfaces, in tris(hydroxymethyl)aminomethane (Tris) buffer solution are used to monitor the time-dependent growth process of a PDA film. Complementary methods as X-ray photoelectron spectroscopy (XPS) and the nanoscale photothermal AFM-IR technique give access to study chemical homogeneity of the probed spots. All of the results are in qualitative agreement and show up new analysis possibilities, even further work is required to resolve the open questions of the chemical structure of PDA films. As proof of principle reaction for biosensor applications the binding of thiol-terminated molecules to the PDA film via Michael-addition was investigated by in situ IRSE.