Download or read book Architecting Small and Bright Upconverting Nanoparticles as a Toolkit for Bioimaging written by Christopher Patrick Siefe and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Upconverting nanoparticles (UCNPs) have the unique ability to absorb light in the near-infrared and emit light in the visible and ultraviolet via a multiphoton process. UCNPs have emerged as a new optical toolkit for tagging, sensing, and drug delivery in biological systems, where they have gained attention due to their: 1) near-infrared rather than visible or ultraviolet excitation, enabling low background noise and high penetration depth through biological tissue, 2) stable emission, without photobleaching or blinking, and 3) biocompatibility. However, small UCNPs are limited in emission efficiency and brightness due to surface quenching of emissive states. Here, we explore ways to improve and alter the emission properties of sub-20 nm UCNPs using nanoparticle architecture, dopant concentration, and host lattice. First, we design and synthesize a unique core-shell-shell nanoparticle architecture for bright upconversion within a sub-20 nm footprint that features: 1) maximum sensitization in the core, 2) efficient energy transfer from sensitizer core to emitter shell, and 3) emitter localization near the surface to enable efficient resonant energy coupling to an external optical probe. We synthesized this novel architecture and compared it with the field-standard core-shell architecture, showing that our novel architecture exhibits up to 2x greater single particle emission and up to 8x greater emission enhancement when coupled to a fluorescent dye. Next, we investigate host lattice effects by synthesizing and comparing sub-20 nm UCNPs composed of 8 different alkaline earth host lattices doped with Yb3+ and Tm3+, passivating these nanoparticles with a biocompatible CaF2 shell. We further explore improvements in efficiency and ultraviolet emission via core-shell design and Yb3+/Tm3+ concentrations in Sr-based host materials. We synthesize and measure sub-20 nm UCNPs with upconversion quantum yield as high as 2.5% and up to 16.5% of their emission in the ultraviolet. Finally, we explore the capabilities of more broadly lanthanide-doped nanoparticles for sensing applications and how we may be able to leverage small and bright nanoparticles for single particle sensing and other future applications. Through this work, we show methods to maintain bright and effective UCNPs in sub-20 nm size regimes, enabling the unique capabilities of UCNPs to applications that require small optical probes for tagging, sensing, and photochemistry.