Adsorption of a primary fibrinogen layer observed by ATR FT-IR spectroscopy. Fibrinogen (Fbg) was adsorbed onto polystyrene from high (500 μg/mL)– and low (20 μg/mL)–concentration fibrinogen solutions (□ and ■, respectively). Inserts show an illustrative arrangement of fibrinogen molecules adsorbed in the end-on (top insert) and side-on orientations.