## 3 Results and Discussion  
### Features of Infrared Spectra from Control Cells  
In FTIR spectra of SH-SYSY neuroblastoma cells, several bands related to the vibrational modes of the biologic molecules of cells constituents (lipids, proteins, DNA, etc.) are present. In Figure 1, the average spectrum of an unexposed sample is reported, obtained for the 3600-900 cm\({}^{-1}\) spectral region. The spectrum appears to be divided into two principal zones with different visible peaks. The range from 3600 to 2600 cm\({}^{-1}\) (Figure 2A,B) is generally indicated as **high wavenumber region** (HWR) and presents bands that are due to the contribution of proteins, lipids, and carbohydrates. In particular, the bands in the range of 3200-3500 cm\({}^{-1}\) are assigned to the amide A (-N-H) stretching motion of peptide backbones of proteins amino acids and O-H stretching of carbohydrate polysaccharides, while the band at \(\approx\)3150 cm\({}^{-1}\) is mainly related to -NH\({}_{3}\)\({}^{+}\) asymmetric stretching of free amino acids. The two peaks at \(\approx\)2960 cm\({}^{-1}\) and \(\approx\)2870 cm\({}^{-1}\) are attributed, respectively, to the asymmetric and symmetric stretching of the methyl groups (-CH\({}_{3}\)) given by cellular proteins and lipids contribution. The structures at \(\approx\)2920 cm\({}^{-1}\) and \(\approx\)2850 cm\({}^{-1}\) are, respectively, due to the asymmetric and symmetric stretching of the methylene groups of membrane lipids (-CH\({}_{2}\)).  
In the so-called **fingerprint region** (1800-900 cm\({}^{-1}\)) (Figure 2C), different peaks that are representative of proteins and nucleic acids are clearly visible. The two peaks at \(\approx\)1650 cm\({}^{-1}\) and \(\approx\)1540 cm\({}^{-1}\) are mainly assigned to the amide I (C=O and C-N) and amide II (N-H and C-N). The band at \(\approx\)1450 cm\({}^{-1}\) is related to symmetric and asymmetric bending of the methylene and methyl groups (-CH\({}_{2}\) and -CH\({}_{3}\)) and to -CH\({}_{2}\) scissoring of proteins and lipids, and the peak at \(\approx\)1400 is due to COO\({}^{-}\) group asymmetric stretching of proteins. The asymmetric and symmetric -PO\({}_{2}\) stretching vibrations of the phosphodieser nucleic acid backbone are associated with the two bands at \(\approx\)1240 cm\({}^{-1}\) and \(\approx\)1085 cm\({}^{-1}\), respectively, with a contribution from C-O-P stretching of protein and lipids.  
The Amide I band (Figure 2D) can be seen as a convolution of the contributions arising from the various secondary structures of proteins; the bands between 1620-1640 cm\({}^{-1}\) and \(\approx\)1690 cm\({}^{-1}\) can presumably be assigned to \(\beta\)-sheet structures with the \(\approx\)1620 and 1690 cm\({}^{-1}\) band characteristic of the anti-parallel \(\beta\)-sheet structures. The band at \(\approx\) 1660 cm\({}^{-1}\) is mainly attributed to \(\alpha\)-helix secondary  
Figure 1: Average spectrum of an unexposed sample in the range 3600–900 cm\({}^{-1}\); the break at 2600–1900 cm\({}^{-1}\) hides a region without interesting signals from biological molecules; data are presented as MEAN \(\pm\) SD.  
structures, while the random structures and \(\beta\)-turns contribute to the bands at \(\approx\)1650 and in the 1670-1685 cm\({}^{-1}\) range, respectively.  
In Figure 2A-D, the deconvolution for the spectra in the regions 3600-3000 cm\({}^{-1}\), 3000-2700 cm\({}^{-1}\), 2000-600 cm\({}^{-1}\), and 1800-1600 cm\({}^{-1}\) are, respectively, shown. In Table S1 (Supplementary Material), the assignments for all the resolved peaks are shown [10; 12; 13; 39; 47]. In Tables S2 and S3 (Supplementary Material), the assignments for the subcomponents of the Amide I region are shown [37; 38; 39].