Experimental and DFT studies of copper nanoparticles as SERS substrates

Nanoparticles can enhance the intensity of susceptible vibrational modes through electromagnetic or chemical enhancement mechanisms responsible for the SERS effect (Surface-enhanced Raman spectroscopy). In the present work, copper nanoparticles (CuNP) with diameters between 3 and 10 nm were obtained by a simple method using rongalite and gelatin. The UV–Vis spectrum showed a well-defined absorption band centered at 570 nm, attributed to the surface plasmon resonance (SPR) of CuNP in a colloidal solution. The SERS effect was analyzed on the pyridine (Py) molecule, observing an enhancement in the radial breathing mode of Py. Complementarily, Cu_4n clusters (with n = 1–5) were modeled under the DFT (Density Functional Theory) framework at the B3LYP (Becke, 3-parameter, Lee–Yang–Parr) approximation level in combination with the LANL2DZ base set (Los Alamos National Laboratory 2 Double-Zeta). After analyzing the molecular descriptors, the Cu_4n-Py interaction study provided hints of SERS behavior.