Label-free plasmonic sensors based on localized surface plasmon resonances of nanostructured noble metal materials usually transduce optical refractive index changes occurring in the vicinity of the nanostructures by optical scattering or by extinction. We demonstrate in experiments that the photoluminescence of plasmonic nanoparticles can also be employed to detect biological molecule binding events efficiently. Photoluminescence probably due to plasmon emission of a single gold nanorod presents a similar resonance peak and resembles the response to a refractive index change observed by scattering. The well-known biotin−streptavidin binding assay was detected successfully using the photoluminescence of an individual isolated nanorod. The localized surface plasmon resonances' responses by scattering in situ with the same nanorod and control experiments were also performed to verify the sensing process. The results evidence that a nanoscale plasmonic sensor can also be archived effectively through the photoluminescence of a single plasmonic nanostructure. Furthermore, key parameters to optimize the photoluminescence based label-free plasmonic sensing are discussed in detail. The photoluminescence provides an alternative way for label-free plasmonic sensing. And it is believed that further exploration of this concept could lead to a whole new class of efficient plasmonic sensors with diverse and novel functionalities.

Anti-Stokes one-photon luminescence from a single gold nanorod is experimentally investigated. The anti-Stokes emission of gold nanorods is enhanced and strongly modulated by localized surface plasmon resonance (LSPR). It is found that the polarization dependence of the anti-Stokes emission is in strong correlation with that of the Stokes emission. Further experiments provide evidence that LSPR significantly enhanced both excitation and emission processes. Moreover, the line shape of the anti-Stokes emission is dependent on the surface temperature, which is related to the distribution of free electrons near the Fermi level. This discovery provides an effective method in principle to probe localized temperature at nanoscale dimension. Here, the reported results about the anti-Stokes emission provide more understanding for the photoemission process from the plasmonic nanostructures.

We report detailed investigations of the photoluminescence (PL) generated from an individual gold nanoflower, a highly branched plasmonic nanoparticle. Compared to nanostructures with simple shapes, such as spheres, nanorods, and bipyramids, nanoflowers exhibit more distinct features, i.e., the PL spectra and far-field emission patterns are strongly dependent on the wavelength and polarization of the excitation light. The experimental results are qualitatively explained using theoretical calculations. In addition, the intrinsic PL signal is highly dominated by localized surface plasmon resonances. The crucial role of plasmonic coupling in complex nanostructures during the plasmon-enhanced PL process is highlighted. The findings contribute to a deeper understanding of the PL properties of metallic nanoparticles. This study will be beneficial for several potential applications, including optical imaging and sensing in the fields of materials science and biology.

Luminescence quantum yields (QYs) of gold nanoparticles including nanorods, nanobipyramids and nanospheres are measured elaborately at a single nanoparticle level with different excitation wavelengths. It is found that the QYs of the nanostructures are essentially dependent on the excitation wavelength. The QY is higher when the excitation wavelength is blue-detuned and close to the nanoparticles' surface plasmon resonance peak. A phenomenological model based on the plasmonic resonator concept is proposed to understand the experimental findings. The excitation wavelength dependent QY is attributed to the wavelength dependent coupling efficiency between the free electron oscillation and the intrinsic plasmon resonant radiative mode. These studies should contribute to the understanding of one-photon luminescence from metallic nanostructures and plasmonic surface enhanced spectroscopy.