Morphological effect on Core@shell AuAg nanoparticles for detecting p-aminothiophenol dimerization by surface-enhanced Raman spectroscopy

A series of non-spherical metallic Au and bimetallic core@shell AuAg nanoparticles (NPs) have been synthesized for SERS improvements. The bimetallic core@shell AuAg NPs were obtained through a controlled overgrowth of an Ag shell onto the surface of two types of non-spherical Au NPs, used as seeds, Au nanooctaheda (Au NOc) and Au nanotriangles (Au NTs). This Ag overgrowth was able to produce bimetallic core@shell structures such as nanocubes and nanopyramids, respectively. Transmission electron microscopy (TEM) was used to determine the particle size and particle morphology for metallic and bimetallic NPs, and energy-dispersive X-ray (EDX) elemental mapping analysis confirmed the core@shell structure of the bimetallic NPs. The plasmonic absorption bands exhibited for each nanosystem were observed by UV–vis spectroscopy. The concentration of Au and Ag in the bimetallic systems was determined by inductively coupled plasma mass spectrometry (ICP-MS). After synthesis and characterization, p-aminothiophenol (PATP) was used as a model analyte to investigate the surface-enhanced Raman spectroscopy (SERS) capabilities of the synthesized metallic and bimetallic nanosystems. In PATP, a dimerization reaction to 4,4′-dimercaptoazobenzene (DMAB) is produced when it is adsorbed onto the surface of certain noble metals. This SERS analysis was performed at 10⁻⁴ M of PATP and by using two different laser wavelengths (532 and 785 nm) in all cases. In this context, we were able to detect the dimerization reaction of PATP to DMAB only for the bimetallic structures and under the 532 nm laser line. Moreover, we have found that the dimerization capacity also depends on the nanoparticle morphology.