## 2 FTIR Microspectroscopy
This is the way the information about the energy is usually given in IR absorption spectroscopy instead of using frequencies or wavelengths (see Figure 2 in the present paper). In the spectra, different contributions from lipids, proteins, and nucleic acids are clearly visible. For identifying these different contributions, deconvolution procedures are usually performed. This analysis consists in writing the complex spectra as a sum of Gaussian-Lorentzian-shaped vibrational modes. Detailed information about the modes was obtained by a nonlinear fitting procedure which had starting conditions (i.e., the starting values of the parameters of the single modes) that were obtained by manual selection. The procedure allows for the determination of the optimized intensity, position, and width of the peaks by using the \(\chi^{2}\) parameter for controlling deconvolution procedure performances [19]. This procedure can also be used for monitoring the changes in the peak position due to the interaction with ionizing radiation [19]. In Figure 2, the results of this analysis performed on IR spectra from normal human MCF-10A breast cells are shown, and in Table 1, the assignments for the different functional groups are reported. The region at approximately 2950-2850 cm\({}^{-1}\) is related to the lipid and protein contributions, the absorption bands in the range at approximately 1750-1500 cm\({}^{-1}\) and in the region 1490-1250 cm\({}^{-1}\) are attributed to protein comp  
Figure 1: Scheme of a Fourier transform infrared spectrometer. in the 1230-1000 cm\({}^{-1}\) range are ascribed to DNA/RNA contributions. From Table 1, it can be noticed that the region at longer wavenumbers (i.e., 3000-3400 cm\({}^{-1}\)) can also offer information on proteins [27]. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Peak (cm\({}^{-1}\))**} & \multicolumn{3}{c}{**Assignment**} \\ \cline{2-4}  & **DNA/RNA** & **Protein** & **Lipid** & **Carbohydrate** \\ \hline
3500–3300 & & & & O–H v \\ \hline
3291 & Amide A (–N–H v) & & \\ \hline
3173 & –NH\({}_{3}\)+ as. N (a. a.) & & \\ \hline
3071 & Amide B (–N–H v, \(\delta\)) & & O–H v \\ \hline
2959 & CH\({}_{3}\) as. v & CH\({}_{3}\) as. v & \\ \hline
2924 & & CH\({}_{2}\) as. v & \\ \hline
2889 & CH\({}_{3}\) s. v & CH\({}_{3}\) s. v & \\ \hline
2852 & & CH\({}_{2}\) s. v & \\ \hline
1643 & Amide I (C=O v, C–N v) & & \\ \hline
1534 & Amide II (C–N v, C–NH \(\delta\)) & & \\ \hline
1448 & CH\({}_{3}\) as. \(\delta\), CH\({}_{2}\) sc. & CH\({}_{3}\) as. \(\delta\), CH\({}_{2}\) sc. & \\ \hline
1394 & COO\({}^{-}\) s. v & & \\ \hline
1304 & Amide III (–N–H \(\delta\), C–N v) & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: FTIR peaks observed in the spectrum of MCF-10A breast cells, with assignments in agreement with the data reported in the literature (see Reference [19] and references therein); as = asymmetric, s = symmetric, v = stretching, \(\delta\) = bending, sc = scissoring, vbr = vibration, a. a. = free amino acids. The indicated position of every peak is the center of the relative Gauss-cross-Lorentzian function obtained from the deconvolution fit. Figure 2: Deconvolution of a μFTIR spectrum acquired from normal human MCF-10A breast cells in the different spectral regions. In the (**A** panel) the high wavenumber region (3600–2600 cm\({}^{-1}\)) is shown, in the (**B** panel) the same is shown for the fingerprint region (1800–900 cm\({}^{-1}\)), in the (**C** panel) the same is shown for the Amide I band region (1740–1580 cm\({}^{-1}\)), and in (**D** panel) the same is shown for the Amide III band region (1350–1180 cm\({}^{-1}\)). Reprinted from Reference [19] under open access conditions.