Plasmon resonant molecular sensing with single gold nanostars

Here we describe the application of single star-shaped gold nanoparticles (nanostars) for localized surface plasmon resonant (LSPR) sensing. The gold nanostars were fabricated by a modified seed-mediated, surfactant-directed nanoparticle synthesis which is known to produce gold nanorods in high yield. Due to the sample heterogeneity, single nanostars were studied by dark-field microspectroscopy. The single particle spectra demonstrate that the plasmon resonances of single gold nanostars are extremely sensitive to the local dielectric environment, yielding sensitivities as high as 1.41 eV photon energy shift per refractive index unit. To test their properties as molecular sensors, single nanostar spectra were monitored upon exposure to alkane thiols (mercaptohexadecanoic acid) and a proteins (bovine serum albumin) known to bind gold surfaces. The observed shifts are consistent with the effects of these molecular layers on the surface plasmon resonances in continuous gold films. The results suggest that LSPR sensing with single nanoparticles is analogous to the well developed field surface plasmon resonance (SPR) sensors, and will push the limits of sensitivity.