Review of Some Interesting Surface Plasmon Resonance-enhanced Properties of Noble Metal Nanoparticles and Their Applications to Biosystems

Noble metal, especially gold (Au) and silver (Ag) nanoparticles exhibit unique and tunable optical properties on account of their surface plasmon resonance (SPR). In this review, we discuss the SPR-enhanced optical properties of noble metal nanoparticles, with an emphasis on the recent advances in the utility of these plasmonic properties in molecular-specific imaging and sensing, photo-diagnostics, and selective photothermal therapy. The strongly enhanced SPR scattering from Au nanoparticles makes them useful as bright optical tags for molecular-specific biological imaging and detection using simple dark-field optical microscopy. On the other hand, the SPR absorption of the nanoparticles has allowed their use in the selective laser photothermal therapy of cancer. We also discuss the sensitivity of the nanoparticle SPR frequency to the local medium dielectric constant, which has been successfully exploited for the optical sensing of chemical and biological analytes. Plasmon coupling between metal nanoparticle pairs is also discussed, which forms the basis for nanoparticle assembly-based biodiagnostics and the plasmon ruler for dynamic measurement of nanoscale distances in biological systems.     

Shape-Controlled Synthesis of Silver Nanoparticles for Plasmonic and Sensing Applications

The localized surface plasmon resonance of a silver nanoparticle is responsible for its ability to strongly absorb and scatter light at specific wavelengths. The absorption and scattering spectra (i.e., plots of cross sections as a function of wavelength) of a particle can be predicted using Mie theory (for a spherical particle) or the discrete dipole approximation method (for particles in arbitrary shapes). In this review, we briefly discuss the calculated spectra for silver nanoparticles with different shapes and the synthetic methods available to produce these nanoparticles. As validated in recent studies, there is good agreement between the theoretically calculated and the experimentally measured spectra. We conclude with a discussion of new plasmonic and sensing applications enabled by the shape-controlled nanoparticles.