Low irradiance multiphoton imaging with alloyed lanthanide nanocrystals

Abstract

Multiphoton imaging techniques that convert low-energy excitation to higher energy emission are widely used to improve signal over background, reduce scatter, and limit photodamage. Lanthanide-doped upconverting nanoparticles (UCNPs) are among the most efficient multiphoton probes, but even UCNPs with optimized lanthanide dopant levels require laser intensities that may be problematic. Here, we develop protein-sized, alloyed UCNPs (aUCNPs) that can be imaged individually at laser intensities >300-fold lower than needed for comparably sized doped UCNPs. Using single UCNP characterization and kinetic modeling, we find that addition of inert shells changes optimal lanthanide content from Yb3+, Er3+-doped NaYF4 nanocrystals to fully alloyed compositions. At high levels, emitter Er3+ ions can adopt a second role to enhance aUCNP absorption cross-section by desaturating sensitizer Yb3+ or by absorbing photons directly. Core/shell aUCNPs 12 nm in total diameter can be imaged through deep tissue in live mice using a laser intensity of 0.1 W cm−2.

Long‐Term Colloidal and Chemical Stability in Aqueous Media of NaYF4‐Type Upconversion Nanoparticles Modified by Ligand‐Exchange

“…Upconversion nanoparticles (UCNPs) established in the last years as versatile luminescent probes due to intense progress in the synthesis enabling complex particle architectures of controlled dimensions . As a consequence, also the photophysical principles of photon upconversion, including luminescence efficiency affected by surface quenching and passivation processes have been excessively studied . The absence of any background fluorescence in biological media due to the unique optical properties of the upconversion of low energy photons in the near‐infrared (NIR) region into high energy emissions in the visible or UV makes this material promising for biological applications.…”

Energy Transfer Networks within Upconverting Nanoparticles Are Complex Systems with Collective, Robust, and History-Dependent Dynamics

“…[4][5] Lanthanide-based colloidal upconverting nanoparticles (UCNPs) do not measurably photobleach even under prolonged single-molecule excitation 4,6 and have found use in NIR optogenetics, [7][8] photodynamic therapy, 9 cellular imaging, 4 super-resolution imaging, [10][11][12] and deep-tissue imaging. 5,[11][12][13] Recently, careful engineering of core-shell UCNP heterostructures has enabled them to be imaged at NIR laser power densities nine or more orders of magnitude lower than with two-photon fluorescence. [13][14] Beyond biological applications, UCNPs have spawned technologies in nanoscale thermometry [15][16] and viscometry, 17 anti-counterfeit labeling, 18 microscale lasers, [19][20] plasmonics, 21 photonic networks, 22 and photovoltaics.…”

“…5,[11][12][13] Recently, careful engineering of core-shell UCNP heterostructures has enabled them to be imaged at NIR laser power densities nine or more orders of magnitude lower than with two-photon fluorescence. [13][14] Beyond biological applications, UCNPs have spawned technologies in nanoscale thermometry [15][16] and viscometry, 17 anti-counterfeit labeling, 18 microscale lasers, [19][20] plasmonics, 21 photonic networks, 22 and photovoltaics. 23 Expanding UCNP applications depends largely on increasing upconversion efficiencies, which requires a deeper understanding for how lanthanide excited states dynamically interact.…”

Emergent Upconversion Sustainable Micro‐Optical Trapping Device

“…Lanthanide‐doped upconversion particles (LUCPs) obeys anti‐Stoke's theorem that can absorb low energy near‐infrared radiation (NIR) and emit visible spectrum line, often applied as bioimaging developer and rear‐sided absorber in the photovoltaic device . Based on this aspect, LUCPs still makes a lot of attention in recent sustainable science and engineering community .…”