Hydroxyapatite Modified with Silver Nanoparticles for Recording the SERS Spectra of Differently Charged Analytes.

The surface of hydroxyapatite (HA) was functionalized with silver nanoparticles by reducing silver nitrate in the presence of glucose or hydrazine hydrochloride. Two types of (HA)Ag nanocomposite were obtained presumably possessing excess negative charge ((HA)Ag-I) or positive charge ((HA)Ag-II). Plasmonic coatings of (HA)Ag-I and (HA)Ag-II nanoparticles were formed on the surface of glass substrates using the droplet deposition method and their structural and spectral properties were studied. A comparative study of the intensity of surface-enhanced Raman scattering (SERS) spectra of cationic and anionic porphyrins CuTMpyP4 and CuTPPS4 as well as rhodamine 6G adsorbed on the surface of both types of nanocomposites was carried out. Plasmonic structures (HA)Ag-I provide the greatest enhancement of the SERS signal for the cationic porphyrin CuTMpyP4, while high spectral intensity is observed for the anionic porphyrin CuTPPS4 adsorbed on films of the (HA)Ag-II composite, which is almost forty times higher than for (HA)Ag-I. For Rh6G molecules with charge +1, the efficiency of the SERS signal amplification by (HA)Ag-II nanostructures is several times higher than by plasmonic films of (HA)Ag-I. Hence, feasibility was demonstrated for obtaining various SERS-active substrates with highly-efficient SERS enhancement for both anionic and cationic analyte molecules by changing the synthesis conditions. [ABSTRACT FROM AUTHOR]