The use of noble metal nanoparticles as optical antennas for the enhancement of spectral signals in the visible and infrared spectral regions can be beneficial for the detection of minute amounts of analytes. Here we propose silica cores with attached gold nano-islands (Au-Si02) for surface enhanced infrared, Raman and visible range spectroscopies of phthalocyaninc analyte.
Luminescence and vibrational spectra of suifonated Zn-phthalocyanine were investigated in detail. Special attention was paid to the possibility to create universal broadband SEIRA- SERS substrates for plasmonic enhancement of spectral signals by using silica cores, decorated by gold nanoparticles. It was shown that these particles are suitable both for the moderate enhancement of fluorescence and substantial enhancement of Raman and IR signals. The Raman active molecules can be attached to the Au nanoparticles by links with the pyrrole rings of Zn- phthalocyanine or due to the formation of chemical bonds between thiol groups and Au nanoparticles.The SERS spectral lines do not show any significant shifts when compared with ordinary Raman scattering. Hence, Au-Si02 nanoparticles are interesting agents for spectroscopic material identification of very thin films and monolayers.
At the same time, the plasmonic influence on the fluorescence of suifonated Zn- phthalocyanine appeared quite weak, which can be explained by the random spacing between the fluorescent centers and Au nanoparticles. This weaker effect can also be explained by the fact that in case of fluorescent measurements we looked on ensembles of sparsely distributed nanoparticles and in case of Raman and IR spectroscopy, the signal from denser layers of nanoparticles was measured. The obtained results can be useful for the elaboration of SEIRA and SERS sensors for the detection of small amounts of chemical reagents and their spectral characterization.