Trace concentrations of polycyclic aromatic hydrocarbons (PAHs) have been successfully detected using surface-enhanced Raman scattering (SERS) spectroscopy. For such purpose, new SERS substrates have been developed, consisting of Ag nanoparticles, either in suspension or immobilized on glass, obtained by a new method and covered by adsorbed self-assembled calix[4]arene molecules. Among the assayed calix[4]arenes, the 25,27-dicarboethoxy-26,28-dihydroxy-p-tert-butylcalix[4]arene host molecule displays analytical selectivity to the PAH guest systems bearing four benzene rings, mainly pyrene. The host-guest interaction mechanism seems to take place through a π-π stacking interaction leading to a charge transfer between the complex and the metallic surface, which may also induce a notable influence on the surface charge of the metallic nanoparticle.

The surface-enhanced Raman scattering (SERS) spectra for phthalimide (PIMH) vacuum evaporated, cast onto silver island films, and from colloidal silver are clearly identified with the formation of a phthalimide−silver complex (chemisorption). The phthalimide−silver complex (PIMAg) has been obtained from the PIMH potassium salt and AgNO3. The Raman scattering spectrum of the isolated complex is in agreement with the SERS spectra of the silver surface complex. The experiments were carried out using three laser lines at 514.5, 633, and 780 nm. The photochemical decomposition of the surface complex is detected with all laser lines. The spectral interpretation is aided using Hartree−Fock and local density functional theory (S-VWN) calculations, carried out to compute simulated SERS spectra using the molecular complex PIMAg and the PIMH. The calculated surface complex (SERS) Raman spectrum using S-VWN was found to be in good agreement with the observed spectrum. The observed Raman spectrum for the surface complex may contain the Raman-active modes allowed in the total irreducible representation of the complex symmetry point group. However, the number of observed vibrations can be reduced due to further constraints introduced by molecular and field orientations at the surface (surface selection rules or propensity rules).

In this work, we have applied surface-enhanced Raman scattering (SERS) and surface-enhanced infrared spectroscopy (SEIR) to study the interaction of nitro polycyclic aromatic hydrocarbons (NPAHs) with metal surfaces. The nitro group confers the polycyclic aromatic hydrocarbons (PAHs) moiety additional electronic and structural characteristics which verify NPAHs−surface interactions. SERS and SEIR spectra suggest that the NPAHs 1-nitropyrene (1NP) and 2-nitrofluorene (2NF) at concentrations of <10-6 M (∼200 ppb) interact with metal surfaces through the nitro group, adopting a perpendicular orientation onto the surface. In both cases, the interaction seems to occur through the O atoms of the nitro groups, which are coplanar to the PAHs fragment. The most efficient interaction was obtained using silver metal colloidal surfaces. The mechanism of interaction with the metal surface is related to the structure of NPAHs:  although a monodentate interaction is deduced in the case of 1NP, a bidentate one seems to occur in the case of 2NF. To complete this study, theoretical Raman vibrational spectra of both free 2NF and their complexes with silver metal clusters were obtained using the local spin density approximation (LSDA) methods with the LAN12DZ basis set. The theoretical calculations were compared to the experimental results, obtaining a good agreement with the SERS and SEIR data.