The change in the surface density of quartz crystal over time in Group 1 to Group 4 is shown in Figure 2. Results of the FTIR showed peaks at 1600 and 1353 cm−1 in the polydopamine spectrum, indicating aromatic ring chains and bonds between the phenyl groups in polydopamine, respectively (Figure 3, PDA group). For the PEG spectrum, the peaks at 1061 and 1123 cm−1 represented the C–O stretching vibration and the O–H bending vibration . The peaks at 3172, 3278, and 3345 cm−1 represented free –OH and –NH3. These peaks were observed in the PEG spectrum but not in the dopamine + PEG spectrum. This suggested that no free –OH and –NH2 could be found in the dopamine + PEG treatment and that PEG was grafted chemically to polydopamine .