## 4 Conclusions  
In summary, we report a simple strategy for the fabrication procedure of the SERS-active substrates with the array of metal nanowires (NWs) using a template-assisted electrodeposition method with commercial tracking membranes (TM). It is possible to choose the proper TM with certain diameter of NWs and its surface density, while template synthesis technology allows varying NWs length. Owing to different length, NWs tend to lean forming bundles with different character of gap hot spots. According to model calculations of electromagnetic field distribution, there is large field enhancement due to the presence of gap hot spots in the spacing between neighboring NWs tips. For different leaning geometries, the E-field enhancement was found to be distributed in the range up to 70 and even more. It corresponds to the estimated SERS enhancement factor up to ~107.  
The applicability of this approach was confirmed by the experiments with Ag-NWs substrates with different NWs length (from 0.6 to 7.7 \(\upmu\)m). The optimal NWs length was found as high as 1.6 \(\upmu\)m in order to obtain maximum SERS spectra intensities. This length corresponds to NWs leaning only by its tips that leads to more effective hot spot formation.  
Also, SERS spectra have been measured for 4-MPBA on two different types of substrates: \"dry\" (analyte was added after substrate drying) and \"wet\" (analyte was added before drying). The intensity of the SERS-signal recorded on the \"wet\" and \"dry\" substrates depends a lot of NWs length. For medium-sized NWs (length from 1 to 3 \(\upmu\)m) the intensity on the \"wet\" substrate is 49% higher than on \"dry\" because of the analyte distribution. Analyte molecules caught between NWs tips are affected by high local electromagnetic field, result in higher SERS signal intensity compared to molecules adsorbed on the top of NWs tips. Finally, for optimal NWs length we achieved an enhancement factor up to ~108 for 4-MPBA on the \"wet\" substrates.  
We assume that our substrates are cost-effective and easy to manufacture. With the proper (optimized) parameters such substrates can be useful for numerous applications where the ability to detect trace levels of chemicals is required.  
Conceptualization, E.P.K., V.P.T. and S.N.A.; Data curation, E.P.K.; Formal analysis, S.A.B., N.L.N., S.N.P., Y.V.G. and A.V.N.; Funding acquisition, Y.V.G. and A.V.N.; Investigation, E.P.K.; Methodology, S.A.B., N.L.N., V.P.T. and S.N.A.; Project administration, E.P.K.; Resources, E.P.K., N.L.N., S.N.P., V.P.T., S.N.A., Y.V.G. and A.V.N.; Software, S.N.P., V.P.T. and S.N.A.; Supervision, E.P.K.; Writing--original draft, E.P.K., V.P.T. and S.N.A.; Writing--review & editing, S.A.B., N.L.N., S.N.P., Y.V.G. and A.V.N. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Ministry of Education of Russia and Ministry of Science and High Education of Russia (project State number AAAA-A20-120061890084-9 \"Physics of nanostructured materials: fundamental research and applications in materials science, nanotechnology and photonics\" and by the Russian Foundation for Basic Research (RFBR), project number 18-29-12099. The experimental technique for spectral analysis of complex organic macromolecules is developed for the purposes of RFBR project number 20-03-00923. SEM images using the equipment of the Center for Collective Use of the Federal Research Center \"Crystallography and Photonics of the Russian Academy of Sciences\".  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflict of interest.