A new route for the elaboration of the polypropylene surface directly modified by 4-amino-4'-nitroazobenzene (Disperse Orange 3) was studied. The synthesis consists of a cold carbon dioxide-plasma treatment followed by a mixed anhydride reaction and Disperse Orange 3 fixation. The quantity of active acid introduced by the plasma treatment was estimated to be 0.7 groups/nm(2) by fluorescence labeling with thionine acetate. The azo-modified surfaces were characterized by Fourier transform infrared, resonance Raman, and X-ray photoelectron spectroscopies. Confocal resonance Raman spectrometry has shown that Soxhlet extraction is effective to eliminate diffused molecules from the material. It was shown that the azo dye molecules are chemically fixed onto the polymer surface.