Control of surface plasmon resonance in out-diffused silver nanoislands for surface-enhanced Raman scattering

Abstract We present the studies of self-assembled silver nanoislands on the surface of silver ion-exchanged glasses. The nanoislands were formed by out-diffusion of reduced silver atoms from the bulk of the glass to its surface. Control of silver ions distribution in the glass by thermal poling after the ion exchange allowed formation of relatively big, up to 250 nm, isolated silver nanoislands while without the poling an ensemble of silver nanoislands with average size from several to tens of nanometers with random size distribution was formed. The nanoislands were characterized using atomic force microscopy and spectral measurements. We used optical absorption spectroscopy for “random” nanoislands and dark field scattering spectroscopy for isolated ones, corresponding spectra showed peaks in the vicinity of 450 nm and 600 nm, respectively. The “random” nanoislands significantly enhanced Raman scattering from Rhodamine 6G, also the modification of Raman signal from deposited on the surface of the samples bacteriorhodopsin in purple membranes was registered

Dark-field spectroscopy of plasmon resonance in metal nanoislands: effect of shape and light polarization

Abstract We present the experimental dark-field scattering studies and the simulation of plasmonic properties of isolated silver nanoislands. The nanoislands were fabricated on a soda- lime glass substrate using silver-sodium ion exchange, subsequent thermal poling and annealing of the processed glass substrate in hydrogen. The morphology of the nanoislands was characterized with atomic force microscopy and scanning electron microscopy; the dimensions were 100-180 nm in base and 80-160 nm in height. We measured and modeled dark-field scattering spectra of the silver hemiellipsoidal nanoparticles differing in size and shape. The SPR position varied from 450 nm to 730 nm depending on the particle shape and dimensions. Both experiments and simulation showed a red shift of the SPR for bigger nanoislands of the same shape. Losing the axial symmetry in nanoislands resulted in the resonance splitting, while their elongation led to an increase in the scattering of p-polarized light

SERS OF BACTERIORHODOPSIN WITH OUT-DIFFUSED SILVER NANOISLANDS

We present the studies on surface-enhanced Raman spectroscopy (SERS) of bacteriorhodopsin in purple membranes using self-assembled silver nanoisland films for Raman signal enhancement. These metal island films were fabricated on soda-lime glass slides subjected to silver-sodium ion exchange in molten Ag0.05Na0.95NO3 at the temperature of 325°C for 20 minutes and subsequent treatment in hydrogen atmosphere at the temperature of 250°C for 10 minutes. The films typically consisted of 20–30 nm closely placed nanoislands. Being tested as SERS substrates for rhodamine 6G the nanoisland films gave the possibility to observe respective characteristic Raman lines from a dried drop of rhodamine 6G dissolved in water in the concentration of 10–6 M. Similarly fabricated substrates were used to obtain SERS spectra of bacteriorhodopsin in purple membranes dispersed in water, and Raman peaks at 1000–1020 cm–1, 1150–1220 cm–1 and 1530– 1570cm–1 were resolved. The substrates made it possible to register characteristic Raman peaks only for an order of magnitude lower concentration of bacteriorhodopsin in contrast to the virgin glass substrate, that is the enhancement of Raman signal was considerably less than for rhodomin 6G. This is supposed to be due to bacteriophodopsin molecules packing in patches, and it prevents bacteriophodopsin in purple membranes from penetration between the nanoislands where the local enhancement of the electric field of exciting light wave is maximal