(355f) Surface Plasmon-Enhanced Selective Molecular Sensing Using Unique Silver Nanoaggregates

Christopher, P., University of Michigan, Ann Arbor
Linic, S., University of Michigan

The selective identification of molecular species in a mixture of species is extremely important for the detection of explosives and biological warfare agent and the mechanistic study of chemical reactions. In general, viable techniques for chemical identification must provide a combination of exceptional sensitivity and molecular selectivity. Recent developments in nanoparticle synthesis and nanofabrication techniques, combined with an increased understanding of plasmonic properties of nanomaterials (mainly silver and gold), have greatly transformed surface-enhanced Raman spectroscopy (SERS) into one of the most promising techniques for highly sensitive molecular identification. The resonant creation of surface plasmons on noble metal nanoparticle surfaces and the subsequent enhancement of local electric fields results in enhanced Raman signals of many order of magnitude, and in some cases even allowing single molecule detection. However, application of SERS technique in the selective identification of trace quantities of targeted species in a mixture of species still remains a difficult task.
In this contribution, we demonstrate that aggregates comprised of different shapes of silver nanoparticles (nanocubes, nanowires and nanospheres) exhibit different enhancement for the C≡C stretching (2219.6 cm-1) and phenyl ring breathing (996.2 cm-1) vibrational modes in SERS of diphenylacetalene (DPA).  UV-vis extinction spectra were collected concurrently with the SERS spectra, allowing us to develop a correlation between the nanoparticle aggregate plasmonic properties and the SERS spectra.  The results show that the unique wavelength dependent plasmon resonance of Ag nanoparticles of different shapes can be utilized to independently control the enhancement of the two monitored vibrational modes. The results indicate that the synthesis of SERS substrates with tailored plasmonic properties allows a novel route towards targeted selective molecular detection.