Lanthanide-doped Nanoparticles.................................................................................................................

Lanthanides and rare earth metals have the ability to convert light between different spectral regions with sharp absorption and emission peaks. By doping them into ceramic hosts to make lanthanide-doped nanoparticles (LNPs), we can achieve optical nanoparticles that don’t photobleach or photoblink and can do both downconversion and upconversion. By customizing the specific dopants, host lattice compositions, and nanoparticle size, we can make LNPs useful for a wide variety of imaging applications, including bioimaging and high energy radiation scintillators.

Upconverting lanthanide-doped nanoparticles (UCNPs) can emit at shorter wavelengths than they absorb at, due to the ladder-like energy structure and long-lived energy states of certain rare earth elements. With a variety of dopants, we can get visible light emission in a rainbow of colors when irradiating with near-infrared (NIR) light. NIR excitation penetrates biological tissue more easily and deeply than ultraviolet or visible light, and their size and biocompatibility make UCNPs excellent candidates for non-perturbative bioimaging.

Furthermore, UCNPs have been shown to respond colorimetrically to externally applied force or pressure. They fill an important gap in the landscape of tools for measuring biological forces. Combined with their stable optical properties and functionalizable surface, UCNPs can become a powerful tool for rapid and minimally invasive bioimaging methods for multiple biological systems and various length scales. In our group, we are tuning UCNP force sensitivity with different host lattice and dopant compositions and nanoparticle sizes. We are also developing polymeric delivery formats for systems from the millimeter scale, in the mouse gastrointestinal tract, to the microscopic scale, with pharyngeal pumping in C. elegans worms, to the single particle level, measuring forces between individual immune cells.

To quantify and calibrate UCNPs’ force-spectral response, we have two primary measurement methods. We use a Diamond Anvil Cell to demonstrate the sensitivity and cyclability of force-spectral response in ensembles of nanoparticles, and a tandem Atomic Force and Confocal Microscope to simultaneously exert force on single particles or particle-embedded polymer units while collecting optical emission signal.