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Silver nanoparticle (AgNP) has wide-spread applications in photovoltaic cell, biological sensors, biomedical devices, surface enhanced Raman scattering (SERS) etc. which are intricately dependent on AgNP shape, size, concentration and aggregation states. Here, the particle size, shape and aggregation dependent dipole and quadrupole surface plasmon resonances are spectroscopically investigated by preparing AgNPs (diameter 10-110nm) using silver nitrate (AgNO3) and sodium borohydride (NaBH4 as reducing agent) in aqueous environment at 0 ∘C. The AgNP UV-Visible spectra showing plasmon-induced dipole and quadrupole modes are corroborated by the theoretical framework of Mie-Gans model and discrete dipole scattering model DDSCAT and different particle sizes, shapes and possible aggregation or clusterization are predicted. All the samples show presence of spherical and nonspherical distribution of AgNP. However, the concentration of nonspherical particle is more for higher concentration of reducing agent as is evidenced by the appearance of quadrapole absorption maxima. The minimum particle size is found at a particular ratio of concentration of AgNO3 and NaBH4. The day variation of AgNP kinetics also signalled the onset of quadrupole deformation of clusters. [ABSTRACT FROM AUTHOR]

Time-resolved polarization-dependent transient absorption has been used to study the plasmonicity of the optical transitions of Ag nanoparticles and nanoclusters. The lack of a measureable polarization anisotropy in the nanoparticles is indicative of the ultrafast electron-electron scattering while the anisotropy with a depolarization timescale of 500 fs observed in the nanoclusters indicates the excitation of a non-plasmonic state. The short lifetime of the anisotropy is a measure of electronic coupling between nearly degenerate states and is thus proposed as a sensitive measurement of the plasmonic content of the optical transitions of nanoclusters. [ABSTRACT FROM AUTHOR]

In this study, we achieved an enhancement of the transmission surface plasmon resonance (T-SPR) intensity by depositing silver nanoparticles (AgNPs) onto a gold grating substrate. The T-SPR spectrum of the gold grating substrate with AgNPs showed a strong and narrow SPR peak located between 650 and 800 nm; the maximum SPR excitation was observed at a 35° angle of incidence. We controlled the distance between the gold grating surface and the AgNPs by using layer-by-layer (LbL) ultrathin films of poly(diallydimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS) to study the distance dependence of the coupling effect between the AgNPs and the gold grating substrate. The distance-dependent T-SPR response of peak position and intensity showed distinctive changes when the intermediate layer was 10 bilayers (∼17 nm) thick. The strongest coupling surface plasmon excitation between the AgNPs and the gold grating substrate was obtained at this layer spacing. Furthermore, we explored the potential of the developed system as a switchable pH sensor. The T-SPR spectrum sensitively changed as the pH switched from acidic (pH 2) to alkaline (pH 12) conditions by the swelling/shrinking of the poly(allylamine hydrochloride) (PAH)/PSS LbL film, respectively, which was deposited between the AgNPs and the gold grating. [ABSTRACT FROM AUTHOR]