Figure 4.

Second derivative spectra analysis of nucleic acids, amide I and lipid regions after SiO₂-NPs exposure. Nucleic acids correspond to symmetric PO₂⁻ at 1090 cm⁻¹, and SiO₂-NPs correspond to 1083 cm⁻¹ spectral band in (a) astrocytes and (b) neurons. The secondary structure of proteins corresponds to the amide I region, which includes the 1627 cm⁻¹ for parallel β-strand, 1639 cm⁻¹ for random coil, and 1654 cm⁻¹ for alpha-helix in (c) astrocytes and (d) neurons. Lipids correspond to 1852 cm⁻¹ for symmetric -CH₂ and 2923 cm⁻¹ for asymmetric -CH₂ in (e) astrocytes and (f) neurons.