Yeechi Chen

Plasmonic Nanoparticle Dimers for Optical Sensing of DNA in Complex Media

We introduce a new sensing modality based on the actuation of discrete gold nanoparticle dimers. Binding of the target DNA leads to a geometrical extension of the dimer, thereby yielding a spectral blue shift in the hybridized plasmon mode as detected by single nanostructure scattering spectroscopy. The magnitude and opposite direction of this shift enabled us to spectroscopically distinguish the target from nonspecific binding and to detect the target in complex media like serum.

Excitation enhancement of CdSe quantum dots by single metal nanoparticles

We study plasmon-enhanced fluorescence from CdSe∕CdS∕CdZnS∕ZnS core/shell quantum dots near a variety of Ag and Au nanoparticles. The photoluminescence excitation (PLE) spectrum of quantum dots closely follows the localized surface plasmon resonance (LSPR) scattering spectrum of the nanoparticles. We measure excitation enhancement factors of ∼3 to 10 for different shapes of single metal nanoparticles.

Quantum dot/plasmonic nanoparticle metachromophores with quantum yields that vary with excitation wavelength.

Coupled plasmonic/chromophore systems are of interest in applications ranging from fluorescent biosensors to solar photovoltaics and photoelectrochemical cells because near-field coupling to metal nanostructures can dramatically alter the optical performance of nearby materials. We show that CdSe quantum dots (QDs) near single silver nanoprisms can exhibit photoluminescence lifetimes and quantum yields that depend on the excitation wavelength, in apparent violation of the Kasha-Vavilov rule. We attribute the variation in QD lifetime with excitation wavelength to the wavelength-dependent coupling of higher-order plasmon modes to different spatial subpopulations of nearby QDs. At the QD emission wavelength, these subpopulations are coupled to far-field radiation with varying efficiency by the nanoprism dipolar resonance. These results offer an easily accessible new route to design metachromophores with tailored optical properties.