## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Substrates Type**} & \multirow{2}{*}{\begin{tabular}{c} **Length of** \\ **Ag-NWWs,** \(\mu\)**m \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Aspect Ratio** \\ **(Length/Diameter)** \\ \end{tabular} } & \multirow{2}{*}{**Type of Substrate**} & \multirow{2}{*}{\begin{tabular}{c} **Mean Intensity** \(\times\) \\ **10\({}^{\circ}\), a.u.** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Standard Deviation** \\ **\(\times\) 10\({}^{\circ}\), a.u.** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **The Ratio of Intensities** \\ **obtained on the “wet”** \\ **and “dry” Substrates** \\ \end{tabular} } \\ \hline \multirow{4}{*}{Short NWs} & 0.6 & 60 & Wet & 1.67 & 0.74 & 1.30 \\ \cline{3-6}  & & & Dry & 1.28 & 0.29 & \\ \cline{3-6}  & 0.7 & 70 & Wet & 3.77 & 0.92 & 1.17 \\ \cline{3-6}  & 1.1 & 110 & Wet & 8.98 & 0.64 & 2.35 \\ \cline{3-6}  & 1.6 & 160 & Wet & 20.18 & 1.37 & 1.46 \\ \cline{3-6} Medium-sized & & & Dry & 13.80 & 1.12 & \\ \cline{3-6} NWs & 2.1 & 210 & Wet & 12.52 & 0.76 & 2.03 \\ \cline{3-6}  & & & Dry & 6.17 & 0.82 & \\ \cline{3-6}  & 2.5 & 250 & Wet & 8.91 & 0.37 & 1.44 \\ \cline{3-6}  & & & Dry & 6.43 & 0.39 & \\ \hline \multirow{4}{*}{Long NWs} & 5 & 500 & Wet & 6.80 & 0.31 & 1.97 \\ \cline{3-6}  & & & Dry & 4.99 & 0.34 & \\ \cline{1-1} \cline{3-6}  & 7.7 & 770 & Wet & 5.57 & 0.83 & \\ \cline{1-1} \cline{3-6}  & & Dry & 3.45 & 0.91 & 1.12 & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the investigated 4-MPBA intensities adsorbed on different types of substrates differs by Ag-NWs length collected in 1571 cm\({}^{-1}\). Figure 5: SERS-spectra of 10 \(\mu\)g/mL 4-MPBA adsorbed on the “wet” (green dash line) and “dry” (red dash-dot line) substrates with 1.1 \(\mu\)m Ag-NWs. For comparison the ordinary Raman spectrum of 4-MPBA is shown (blue solid line): brightest Raman spectral peak at \(\sim\)1600 cm\({}^{-1}\) (in enlarged scale in the dashed circle insert). On the insert chemical structure of the analyte molecule is shown. Figure 6 shows the dependence of the SERS-spectra on the Ag-NWs length. Table 1 summarizes SERS intensities for 4-MPBA molecules adsorbed on Ag-NWs substrates with different length. With the length of the Ag-NWs in the range 3-12 \(\upmu\)m (long nanowires), the signal intensity recorded on the \"wet\" substrate is 30% higher than from the \"dry\" one. With the length of the Ag-NWs from 1 to 3 \(\upmu\)m (medium-sized nanowires), the signal intensity recorded on the \"wet\" substrate is 49% higher. On substrates with Ag-NWs with a length of less than 1 \(\upmu\)m (short nanowires), there is a slight increase in intensity in the case of \"wet\" NWs (less 30%), since Ag-NWs hardly lean due to their too short length. Therefore, we deal with the simple array with non-leaning Ag-NWs, and the signal amplification is only due to the \"lightning rod\" effect. The difference of SERS-signals caused by Ag-NWs length can be explained by the different leaning feature. In the case of \"medium-sized NWs\", units of them are leaning partially along their length, so the Ag-NWs tips are parallel for the case of \"dry\" substrates. For the \"wet\" substrates, Ag-NWs tips are also parallel in the center of the bundle and few of them slightly diverge apart at the bundle edges, forming bigger spacing between their tips-- in that spacing gap hot spots are presented by analogy with the colloidal solutions (Figure 7b). As it can be from the SEM images (Figure 7), exactly the \"medium-sized NWs\" are able to form vertical bundles, in which individual NWs fit tightly to each other, being located almost parallel. When the Ag-NWs are \"long\", dozens of the neighboring Ag-NWs tend to lean and the bundles become bigger with the increase in NWs length (Figure 7a), so that long NWs can no longer be positioned vertically (due to the combination of their mass and elastic properties) and they lean on each other, forming nano-contacts of the \"tip-surface\" type.