###### Abstract
It is generally considered a valuable tool for identifying substances according to their characteristic spectrum, which is sometimes referred to as their spectroscopic fingerprint. This concept can also be applied to complex biological molecules or even whole cells and bacteria [9; 10]. However, Raman spectroscopy is limited by its low sensitivity, which makes virus detection quite challenging. As viruses are typically small (25-400 nm, [11]) in comparison to the excitation wavelength, large quantities are required in order to obtain pure spectra. Usually, the virus particles are embedded in a sample matrix with numerous other (Raman-active) components as they are raised in a cell culture or stem from a patient specimen, i.e., a bodily fluid. The other components (for example, proteins, nucleic acid, inorganic salts, buffer compounds) will also contribute to the collected Raman spectra and can hamper an identification based on specific bands, if no purification steps are applied. Such sample preparation can also be a challenging and costly task and is accompanied by a large amount of partly manual laboratory work. The application of advanced techniques such as ultracentrifugation [12], ultrafiltration [13] or affinity chromatography [14] can be time-consuming and require great expertise and/or expensive devices, as well as a lab with an appropriate biosafety standard. Therefore, other detection schemes are often applied in combination with Raman spectroscopy, which do not require purified virus samples. Instead of detecting the virus particles themselves, the presence of specific antibodies, nucleic acids [15] or a change of the overall composition of a certain body fluid [16; 17] can be used as leverage points. The combination of those strategies with statistics-based analysis methods, such as chemometrics, then enables sample classification if the database is large enough. Quite a few approaches are based on surface-enhanced Raman spectroscopy (SERS), which employs metallic nanoparticles or nanostructures for improving the technique's sensitivity through plasmonic enhancement [18; 19; 20]. As the physical phenomenon is, by definition, highly surface-sensitive, unspecific absorption must be avoided. The metallic substrates or particles can be functionalized with specific molecules (i.e., antibodies or proteins) and serve as capture elements and/or their structure can also function as a size-selective enrichment tool [21]. For example, [PERSON] et al. developed a SERS biosensor by decorating magnetic microparticles both with Au nanoparticles and the ACE2 receptor as selective capture elements for SARS-CoV-2 [22]. These particles enable the virus to be isolated from the sample matrix, and when combined with an Au nanoneedle array, it allows for a highly sensitive detection of SARS-CoV-2 from nasal swabs. Another possibility to characterize viruses is to focus on their protein structure. [PERSON] et al. observed that the SERS spectra of SARS-CoV-2 are dominated by protein contributions [23]. A spectroscopic investigation of pure virus proteins might bring even deeper insight into the changes that occur on the molecular level upon the mutation of virus strains. However, some of these sophisticated approaches also come with complex issues of reproducibility and thermal stability, and are thus not yet suitable for routine use and mass production. We aimed at developing a strategy that allows viruses to be detected using conventional Raman spectroscopy, i.e., without the requirement for plasmonically active SERS substrates [18; 19; 20]. The summary of the proposed sample preparation scheme is displayed in Figure 1. For significantly reducing the difficulty of the task to identify a virus only based on its Raman signature, we implemented a specific capture probe in the sample preparation process, so that, ultimately, only the presence of the virus particles needs to be verified via the Raman spectrum.