## 3 Results and Discussion
Interestingly, the regions selected by GA for SERS comparison almost completely overlap with regions which were selected  
Figure 3: The most informative SERS spectral bands and regions as selected by GA for differentiation between: (**a**) AD (all stages) and HC serum samples and (**b**) AD (all stages) and OD serum samples. Selected regions are depicted in red on the average SERS pattern for serum of all classes in order to make comparisons. in comparisons of conventional Raman spectroscopic datasets identified for the same purpose [27]. This shows the consistency of the applied method for the classification of blood serum spectral datasets obtained using different Raman spectroscopic techniques. Further, the tentatively identified set of molecules listed in Tables 2 and 3 can be used for future evaluation of the spectroscopic signature for AD. For this study, the selected regions that are the most significant differentiation were used for the rest of analysis, including during the building of the ANN models. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **GA Region** &
\begin{tabular}{c} **Peak** \\ **Position** \\ \end{tabular} & **Vibrational Mode** & **Contributions [15; 20; 24; 62; 63]** \\ \hline  & & & \({}^{\text{v}}\)(C-S), \({}^{\text{v}}\)(C-C), & & \\
1 & 674–710 & 683 & (C-N), (CH\({}_{2}\)), & adenine, glycine, tryptophan, histidine, proline, oleic acid, triolein, mannose, citric acid, coenzyme A, & acetyl coenzyme A, glutathione, phospholipids \\ \hline  & & & \({}^{\text{\delta}}\)(C-O-H), & guanine, glycine, valine, histidine, proline, & \\
2 & 899–973 & 886 & \({}^{\text{v}}\)(C-C), \({}^{\text{v}}\)(CH\({}_{3}\)), & & hydroxyproline, glutathione, \(\alpha\) helix, fatty acids, \\  & & 958 & \({}^{\text{\delta}}\) Ring vibration, & cholesterol, mannose, galactosamine, & \\  & & & (CH\({}_{2}\)), (C-O-C) & N-acetyl-D-glucosamine & \\ \hline  & & & & \({}^{\text{\delta}}\)(C-O-H), & adenine, glycine, serine, glutamate, tryptophan, \\
3 & 1087–1123 & 1071 & \({}^{\text{v}}\)(C-N), \({}^{\text{v}}\)(C-C), & histidine, fatty acids, mannose, glucose, lactose, & \\  & & 1134 & \({}^{\text{v}}\)(C-O) & galactosamine, N-acetyl-D-glucosamine, acetyll \\  & & & 1134 & \({}^{\text{v}}\)(C-O) & coenzyme A, D-fructose-6-phosphate, & \\  & & & & glutathione, phospholipids & \\ \hline  & & & & \({}^{\text{v}}\): stretching mode; \({}^{\text{\delta}}\): bending mode. & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Tentative assignments of the most important regions in the SERS spectrum of blood serum for the discrimination between AD and HC, as determined by GA. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **GA Region** &
\begin{tabular}{c} **Peak** \\ **Position** \\ \end{tabular} & **Vibrational Mode** & **Contributions [15; 20; 24; 62; 63]** \\ \hline
1 & 448–485 & 495 & Ring torsion vibration, \({}^{\text{v}}\)(N-C-S) & & guanine, arginine, valine, glutamate, tyrosine, \\  & & & & \({}^{\text{v}}\) tryptophan, mannose, glycologen, acetyll coenzyme A, \\  & & & & \({}^{\text{v}}\)(N-C-S) & & acetocate \\ \hline  & & & & uracil, alanine, phenylalanine, glutamate, tyrosine, \\
2 & 523–560 & 530 & \({}^{\text{v}}\)(S-S) disulfide stretching in proteins & & tryptophan, cysteine, mannose, fructose, \\  & & & & & galactosamine, N-acetyl-D-glucose, \\  & & & & & phosphoenolpyruvate, acetyll coenzyme A, \\  & & & & & \\ \hline
3 & 598–635 & 590 & \({}^{\text{v}}\)(C-S), \({}^{\text{v}}\)\({}_{4}\)(PO\({}_{4}\)\({}^{3}\)-) & ascorbic acid, glutamate, tryptophan, methionine, \\  & & & & tyrosine, lactose, N-acetyl-D-glucosamine, pyruvate, \\  & & & & acetyl coenzyme A, phosphatidylinositol \\ \hline
4 & 749–785 & 742 & \({}^{\text{\delta}}\) Ring vibration & \({}^{\text{\delta}}\)(C-O-H), & cytosine, thymine, uracil, glutamate, tyrosine, \\  & & & & tryptophan, proline, N-acetyl-D-glucose, \\  & & & & & tryptophan, histidine, phosphate,phospholipids \\  & & & & & riboflavin, pyrimidine, phosphatidylserine \\ \hline \hline \end{tabular}
\end{table}