## 3 Results and Discussion
However, in this latter case the differences of the peak intensities between the control and the exposed samples (see Figure 3 of [13]) are more prominent with respect to those shown in Figure 2. Such a behavior is related to a marked inter-individual variability of the cellular response to the EMFs-induced stress. Our results are also compatible with \begin{table}
\begin{tabular}{c c c} \hline
**Spectral Range of Raman** & **Present Work (cm\({}^{-1}\))** & **Attribution** \\
**Features (cm\({}^{-1}\)) [26]** & **Present Work (cm\({}^{-1}\))** & **Attribution** \\ \hline
780–788 & 785 & (O-P-O str., n.a.) + (ring breathing, n.a.) \\ \hline
810–859 & 830, 853 & (O-P-O str., n.a.) + (ring breathing, Tyr.) \\ \hline  & 895, 932, 970 & vibrational modes of glass substrate \\ \hline
1000–1006 & 1003 & (symmetric ring breathing, Phe) \\ \hline
1031–1033 & 1030 & (C-H in-plane bend., Phe) \\ \hline
1053–1064 & 1060 & (C-O C-C, c) + (C-N str., p.) + (C-C str., l) \\ \hline
1087–1096 & 1092 & (PO\({}_{2}^{-}\) str., n. a.) \\ \hline
1123–1128 & 1125 & (C-N str., p.) + (C-O, c.) + (C-C str., l.) \\ \hline
1163–1176 & 1175 & (C-H bending, Tyr) \\ \hline
1220–1284 & 1260 & (Amide III, p.) \\ \hline
1300–1313 & 1305 & (CH\({}_{2}\) twist., l.) \\ \hline
1335–1343 & 1340 & (CH\({}_{3}\) def., CH\({}_{2}\) wagg., p. and n.a.) \\ \hline
1360–1379 & 1380 & (CH bend., Trp) + (ring breathing, n.a.) + (CH\({}_{3}\) bend., l.) \\ \hline
1436–1460 & 1450 & (CH\({}_{2}\) sciss., l.) + (CH\({}_{2}\) sciss., p.) \\ \hline
1485–1490 & 1485 & (ring breathing, n.a.) \\ \hline
1573–1582 & 1580 & (ring breathing, n.a.) \\ \hline
1615–1618 & 1615 & (C=C, Tyr., Trp.) \\ \hline
1655–1685 & 1662 & (Amide I, p.) + (C=C str., l.) \\ \hline \end{tabular}
\end{table} 
Table 1: Attribution of Raman spectral features, according to the literature [26] and present work results. Abbreviations: Phe: phenylalanine; Tyr: tyrosine; Trp: tryptophan; p: protein; c: carbohydrate; l: lipid; n.a. : nucleic acid; str: stretching; bend: bending; wagg; twist: twisting; sciss: scissoring. those found by other authors, who observed chromosomal modifications [9; 10] and a larger amount of micronucleiei [30] in human lymphocytes exposed to radiofrequency radiation. As for the mechanisms by which EMFs exposure can influence DNA, the interaction could involve the displacement of electrons in the H-bonds of DNA. In fact, electrons can move in DNA and biochemical data suggest that EMFs can accelerate electron transfer [31]. As average spectra of exposed and unexposed cells show small differences of spectral intensity, the PCA method was applied to each time-dependent spectral data set for a further comparison of Raman spectra differences. In fact, the main peculiarity of PCA technique is the possibility to provide, for a given principal component (PC), the loading values, which estimate the variance of the intensity signal for each wavenumber value. Therefore, the loading plots consist of spectral data which give information about the wavenumber values at which the Raman signals furnish the main variability inside the data set, corresponding to changes in the molecular components contributing to the spectra [18]. Figure 2: Average Raman spectra of control (black line) and exposed (red line) PBLM cells. The PBLM cells were exposed for 20 (**a**), 12 (**b**) and 5 (**c**) hours. As a result of the performed PCA, Raman spectra of exposed and unexposed PBLM cells do not exhibit significantly different principal component (PC) score values for each investigated exposure time, as shown in Figure 3 for PC1 and PC2. This behavior can be due either to the spatial inhomogeneity of a cellular sample or to the relative weakness of the Raman signal from cells: these features result in relatively noisy spectra. When the spectra from a data set are widely spread and not clearly differentiated, as occurs in the score plots Figure 3, mean PC1 score values can be used to characterize the groups of exposed and unexposed PBLM cells.