Characterization of SiO2-NPs by ATR-FTIR spectroscopy, scanning electron microscopy, and ζ-potential. (a) An infrared spectrum of SiO2-NPs as pure powder. IR spectral bands correspond to 458 cm−1 for Si-O out of plane deformation; 800 cm−1 for Si-O bending, 961 cm−1 for Si-OH stretching, 1083 cm−1 for Si-O-Si asymmetric stretching, 1638 cm−1 for C-O bending, 3361 cm−1 of -OH. (b) An infrared spectrum of SiO2-NPs suspended in saline solution. (c) Comparison of spectral bands of pure powder SiO2-NPs vs. suspended in saline. (d) Representative image of the scanning electron microscopy and ζ-potential values of SiO2-NPs suspended in BME and DMEM. The SEM image shown corresponds to 80,000×, scale bar 100 nm.