Nanoplasmonic Upconverting Nanoparticles as Orientation Sensors for Single Particle Microscopy.

We showed that the anisotropic disk shape of nanoplasmonic upconverting nanoparticles (NP-UCNPs) creates changes in fluorescence intensity during rotational motion. We determined the orientation by a three-fold change in fluorescence intensity. We further found that the luminescence intensity was strongly dependent on the particle orientation and on polarization of the excitation light. The luminescence intensity showed a three-fold difference between flat and on-edge orientations. The intensity also varied sinusoidally with the polarization of the incident light, with an Imax/Imin ratio of up to 2.02. Both the orientation dependence and Imax/Imin are dependent on the presence of a gold shell on the UCNP. Because the fluorescence depends on the NP's orientation, the rotational motion of biomolecules coupled to the NP can be detected. Finally, we tracked the real-time rotational motion of a single NP-UCNP in solution between slide and coverslip with diffusivity up to 10-2 µm2s-1.

Enhancement of Upconverted Fluorescence by Interference Layers.

Upconverting nanoparticles show potential applications in the field of photovoltaics and array-based detection devices. While fluorescence enhancement using interference of incident radiation is well known in Stokes-shift type systems such as fluorescent dyes; the effect of such interference geometry in nonlinear Anti-Stokes type emission, such as in upconversion rare earth photophysics is demonstrated for the first time. This work describes in detail the influence of the interference modulation on both the excitation (interion energy transfer) and radiative decay with nonradiative decay processes active between emissive levels. These effects are illustrated in the thickness dependence of the decay rate and rise time. Single particle upconverted spectra and time-resolved measurements show concurrent optimization of the infrared absorption and emission at 540 and 650 nm, with an average enhanced emission of 20 times at λ = 540 and 45 times at λ = 650 nm, dependent on the interference layer thickness and on the excitation intensity. The experimental results are correlated with finite element modeling. Both experiments and calculations show emission enhancement at an interference layer thickness of about 740 ± 20 nm, where such tolerance and the planar design, leads to ease in implementation in applications.

Nanofabricated upconversion nanoparticles for photodynamic therapy.

We present a novel process for the production of three-layer Composite Nanoparticles (CNPs) in the size range 100-300 nm with an up-converting phosphor interior, a coating of porphyrin photosensitizer, and a biocompatible PEG outer layer to prevent clearance by the reticuloendothelial system. We show that these CNPs produce millimolar amounts of singlet oxygen at NIR intensities far less than other two-photon techniques.