Enhancement of Raman Spectra of (Bio)Analytes Using Copper Nanostructures in the (Deep) UV Spectral Range

Raman spectroscopy is an important approach in bioanalytics due to its high specificity and provides clear information about the chemical structure of the molecules under investigation - without the need for labels. In Surface Enhanced Raman Scattering (SERS), the molecules under investigation interact with rough metal surfaces, which enables ultra-sensitive detection down to individual molecules. For measurements in the visible and NIR spectrum (418-785 nm), gold, silver and copper nanostructures are highly efficient. Wavelengths from the deep UV to IR spectral range are used for excitation, allowing the identification and differentiation of individual components down to microorganisms and tissues. The UV range, in particular, is very promising for proteins because they specifically absorb light below 400 nm, thereby resonantly amplifying vibrational modes characteristic of the peptide backbone and some amino acid residues.<br/>A large number of different fabrication strategies are available for the fabrication of a powerful SERS substrate. However, despite its enormous potential, SERS has not yet been applied in routine bioanalytical applications, often due to the challenges of preparing low-cost/efficient SERS surfaces with high reproducibility and signal amplification properties.<br/>In the present work, for the first time on the basis of copper nanostructures deposited on silicon surface using galvanic displacement effect, we found significant enhancement of Raman signal of biomolecules (adenine, guanine, riboflavin) by copper nanostructures at excitation wavelengths of 244, 257, 325 nm. The obtained copper surfaces show significant chemical resistance to oxidation, which may be related to the binding of biomolecules to the surface. In addition, to study the interaction of biomolecules with the copper surface and possible energy transfer, the copper surface was coated with a layer of silica deposited by ALD. Differences in the intensity of the Raman signal on adenine were obtained depending on the thickness of the silicon dioxide layer, which can be related to the efficiency of the transition of electrons through the dielectric layer. A more detailed discussion of the discovery will be presented in the paper. The use of copper as a plasmonic material could play a crucial role in the field of SERS research, as this issue is very poorly understood and studied. According to existing publications, the SERS activity of copper nanostructures is associated only with the near-infrared spectral range (600-800 nm), where copper exhibits weaker SERS activity compared to gold or silver nanostructures. From this point of view, our discovery may provide a new stimulus for the development of materials for UV-SERS applications.