Targeted Single Particle Tracking with Upconverting Nanoparticles

Abstract

Single particle tracking (SPT) is a powerful technique for real-time microscopic visualization of the movement of individual biomolecules within or on the surface of living cells. However, SPT often suffers from the suboptimal performance of the photon-emitting labels used to tag the biomolecules of interest. For example, fluorescent dyes have poor photostability, while quantum dots suffer from blinking that hampers track acquisition and interpretation. Upconverting nanoparticles (UCNPs) have recently emerged as a promising anti-Stokes luminescent label for SPT. In this work, we demonstrated targeted SPT using UCNPs. For this, we synthesized 30 nm diameter doped UCNPs and coated them with amphiphilic polymers decorated with polyethylene glycol chains to make them waterdispersible and minimize their nonspecific interactions with cells. Coated UCNPs highly homogeneous in brightness (as confirmed by a single particle investigation) were functionalized by immunoglobulin E (IgE) using a biotin−streptavidin strategy. Using these IgE-UCNP SPT labels, we tracked high-affinity IgE receptors (FcεRI) on the membrane of living RBL-2H3 mast cells at 37 °C in the presence and absence of antigen and obtained good agreement with the literature. Moreover, we used the FcεRI-IgE receptorantibody system to directly compare the performance of UCNP-based SPT labels to organic dyes (AlexaFluor647) and quantum dots (QD655). Due to their photostability as well as their backgroundless and continuous luminescence, SPT trajectories obtained with UCNP labels are no longer limited by the photophysics of the label but only by the dynamics of the system and, in particular, the movement of the label out of the field of view and/or focal plane.

Revealing the Existence of Long-Range Liquid–Liquid Interfacial Potential in Phase-Transfer Processes

“…This suggests that the nanoparticles far from the interface display normal Brownian motion (i.e., α = 0.91 and 0.94 for the far x - and y -component, respectively). A slight deviation from α = 1 could arise from errors due to locating the actual positions of the nanoparticles. , On the other hand, while the y -component of the nPTCs close to the interface exhibit normal diffusive motion (α = 0.92), the x -component is clearly subdiffusive (α = 0.54, Figure G) . The 1D diffusion coefficients, obtained from MSD = 2 Dt , also did not show a significant difference between the near-interface y -component ( D = 1.5 μm 2 s –1 ) and the far-interface x - and y -components ( D = 1.6 and 1.8 μm 2 s –1 , respectively).…”

Photon upconversion of Nd3+–Yb3+–Tb3+ doped core–shell–shell–shell nanoparticles

“…Lanthanide-doped UCNPs can absorb two or more photons and emit a single photon with a shorter wavelength. 1 Anti-Stokes-shifted luminescent materials have been widely applied in displays, anti-counterfeiting, biological labelling, and other fields due to their sharp emission bands, high light stability, and low biological toxicity. 2–7 Compared to typically 980 nm excited NaYF 4 :Yb/Er or NaYF 4 :Yb/Tm UCNPs, in which Er 3+ or Tm 3+ ions serve as activators and Yb 3+ ions are used as sensitizers to absorb 980 nm NIR light, 6,8–14 Nd 3+ doped UCNPs can be excited by an 808 nm laser and then transfer energy to the activator (for example, Er 3+ ) through Yb 3+ as an energy transfer bridge (Nd 3+ → Yb 3+ → Er 3+ ), 15,16 greatly reducing the thermal effect caused by the strong absorption of water under 980 nm excitation.…”