## 3 Results and Discussion  
The averaged spectrum of normalized Raman signals collected from a mixture of control PBLM cells related to different human subject is shown in Figure 1. Many spectral features, due to vibrational modes of functional groups inside nucleic acids, proteins, lipids and carbohydrates components are present. Assignment of the labeled Raman peaks, according to the results reported in literature [26], is shown in Table 1. In particular, the main peaks related to protein vibrational modes are centred at about 1003, 1260, 1615 and 1662 cm\({}^{-1}\), whereas resolved vibrational peaks due to nucleic acid components are located at 785, 1092 and 1580 cm\({}^{-1}\). The spectral feature visible as a shoulder at 1485 cm\({}^{-1}\) is also due to nucleic acid components. As for the contribution to the spectrum of the features related to lipid components, except the peak at 1305 cm\({}^{-1}\), it is overlapped to that of other components in the peaks at 1060, 1380 and 1450 cm\({}^{-1}\). Other peaks related to different cellular components are centred at 830, 853, 1125 and 1340 cm\({}^{-1}\). Overall, the spectrum in Figure 1 is quite similar to those reported in literature for primary human lymphocyte and monocyte cells [27], as well as lymphocyte [28] and monocyte [29] cell lines. In fact, the Raman spectra representative of such two different types of cells are characterized by Raman features having similar spectral positions but different relative intensity: in particular, the intensity ratio of DNA to protein peaks is larger in the lymphocyte spectra than in monocyte spectra. Normalized and averaged Raman spectra from a mixture of control and exposed PBLM cells, for exposure time of 20, 12 and 5 hours at 200 V/m, are shown in Figure 2a-c. Although the spectra of  
Figure 1: Normalized and averaged Raman spectrum of about 30 unexposed peripheral blood lympho-monocyte (PBLM) cells, measured by focusing the exciting Ar+ laser beam on cell nucleus. The labels refer to the spectral position of the most important Raman features [26], whose attribution is reported in Table 1.  
control and exposed cells of Figure 2 are very similar, the relative intensity of some Raman features changes in the spectra of exposed cells with respect to the control ones, particularly for exposure time of 20 and 12 h. The most evident intensity changes are mainly related to Raman features due to vibrational modes of nucleic acids: (i) the ring stretching mode of DNA bases and the O-P-O stretching mode of phosphodieser bond of phosphate group of DNA at 785 cm\({}^{-1}\), (ii) the PO\({}_{2}\)\({}^{-}\) phosphodioxy bond of phosphate group of DNA at 1092 cm\({}^{-1}\), (iii) the CH\({}_{3}\) and CH\({}_{2}\) bending modes at 1340 cm\({}^{-1}\), and (iv) the ring breathing mode of DNA bases at 1485 cm\({}^{-1}\) and 1578 cm\({}^{-1}\). Some relative intensity changes are also evident in protein-related Raman features: (i) the breathing mode of phenylalanine at 1003 cm\({}^{-1}\), (ii) the CH\({}_{2}\) scissoring modes at 1450 cm\({}^{-1}\) (partly due to lipid component), (iii) the C=C stretching mode of phenylalanine, tyrosine and tryptophan at 1615 cm\({}^{-1}\) and (iv) the amide I mode at 1662 cm\({}^{-1}\). The common characteristic of such spectral changes mainly consists in the intensity decrease of the nucleic acid related peaks with respect to the protein ones. This can be attributed to modification of DNA and proteins bonds in the cells after EMF exposure. In particular, the lowering of the signals related to DNA features after exposure to the EMFs suggests some small change in the DNA dynamic structure induced by the EMF, particularly for 12 and 20 exposure hours. We observed a decrease of Raman intensity of nucleic acid peaks also for PBLM cells isolated from exposed blood collected by single healthy subjects [13].