3.5 Functional groups on the cell surface
The peaks of ATR-IR spectra located at 977 and 1000 cm−1 could be assigned to Si-O vibration (Fig. 5) [30]. The peaks at 1020 cm-1 represented the vibration of Si-O-Si [31], which disappeared after Mt and Pal addition (Fig. 5). Peaks at 1387 cm-1 and 1460 cm-1 were assigned to -COOH and P-O-H groups of polysaccharides, while the bands at 1534 and 1650 cm-1were contributed by N-H and C=O groups in proteins [22], which declined after the addition of Mt and Pal, indicating that the content of amide group decreased [32,33]. The peak at 3548 cm-1 was related to the stretching vibration of -OH [34]. The weakened peak intensity (for peaks 1500-1600 and 2900-3500 cm-1) were possibly due to the binding of functional groups with clay particles.