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1. Blinking characteristics of organic fluorophores for blink-based multiplexing

   https://doi.org/10.1038/s42004-024-01106-5  

   Seabury, Amelia G.; Khodabocus, Alisha J.; Kogan, Isabelle M.; Hoy, Grayson R.; DeSalvo, Grace A.; Wustholz, Kristin L. (January 2024, Communications Chemistry)

   Abstract Single-molecule fluorescence experiments have transformed our understanding of complex materials and biological systems. Whether single molecules are used to report on their nano-environment or provide for localization, understanding their blinking dynamics (i.e., stochastic fluctuations in emission intensity under continuous illumination) is paramount. We recently demonstrated another use for blinking dynamics called blink-based multiplexing (BBM), where individual emitters are classified using a single excitation laser based on blinking dynamics, rather than color. This study elucidates the structure-activity relationships governing BBM performance in a series of model rhodamine, BODIPY, and anthraquinone fluorophores that undergo different photo-physical and-chemical processes during blinking. Change point detection and multinomial logistic regression analyses show that BBM can leverage spectral fluctuations, electron and proton transfer kinetics, as well as photostability for molecular classification—even within the context of a shared blinking mechanism. In doing so, we demonstrate two- and three-color BBM with ≥ 93% accuracy using spectrally-overlapped fluorophores. 

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2. Perspective on functional metal-oxide plasmonic metastructures

   https://doi.org/10.1063/5.0134141  

   Sadeghi, Seyed M.; Wing, Waylin J.; Gutha, Rithvik R. (February 2023, Journal of Applied Physics)

   Plasmonic nanostructures and metasurfaces are appealing hosts for investigation of novel optical devices and exploration of new frontiers in physical/optical processes and materials research. Recent studies have shown that these structures hold the promise of greater control over the optical and electronic properties of quantum emitters, offering a unique horizon for ultra-fast spin-controlled optical devices, quantum computation, laser systems, and sensitive photodetectors. In this Perspective, we discuss how heterostructures consisting of metal oxides, metallic nanoantennas, and dielectrics can offer a material platform wherein one can use the decay of plasmons and their near fields to passivate the defect sites of semiconductor quantum dots while enhancing their radiative decay rates. Such a platform, called functional metal-oxide plasmonic metasubstrates (FMOPs), relies on formation of two junctions at very close vicinity of each other. These include an Au/Si Schottky junction and an Si/Al oxide charge barrier. Such a double junction allows one to use hot electrons to generate a field-passivation effect, preventing migration of photo-excited electrons from quantum dots to the defect sites. Prospects of FMOP, including impact of enhancement exciton–plasmon coupling, collective transport of excitation energy, and suppression of quantum dot fluorescence blinking, are discussed. 

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3. Synthesis and Characterization of Dye-Doped Au@SiO ₂ Core-Shell Nanoparticles for Super-Resolution Fluorescence Microscopy

   https://doi.org/10.1177/00037028221121357  

   Thompson, Shelby; Jorns, Mychele; Pappas, Dimitri (October 2022, Applied Spectroscopy)

   Dye-doped nanoparticles have been investigated as bright, fluorescent probes for localization-based super-resolution microscopy. Nanoparticle size is important in super-resolution microscopy to get an accurate size of the object of interest from image analysis. Due to their self-blinking behavior and metal-enhanced fluorescence (MEF), Ag@SiO₂and Au@Ag@SiO₂nanoparticles have shown promise as probes for localization-based super-resolution microscopy. Here, several noble metal-based dye-doped core-shell nanoparticles have been investigated as self-blinking nanomaterial probes. It was observed that both the gold- and silver-plated nanoparticle cores exhibit weak luminescence under certain conditions due to the surface plasmon resonance bands produced by each metal, and the gold cores exhibit blinking behavior which enhances the blinking and fluorescence of the dye-doped nanoparticle. However, the silver-plated nanoparticle cores, while weakly luminescent, did not exhibit any blinking; the dye-doped nanoparticle exhibited the same behavior as the core fluorescent, but did not blink. Because of the blinking behavior, stochastic optical reconstruction microscopy (STORM) super-resolution analysis was able to be performed with performed on the gold core nanoparticles. A preliminary study on the use of these nanoparticles for localization-based super-resolution showed that these nanoparticles are suitable for use in STORM super resolution. Resolution enhancement was two times better than the diffraction limited images, with core sizes reduced to 15 nm using the hybrid Au–Ag cores. 

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4. Core size does not affect blinking behavior of dye-doped Ag@SiO ₂ core–shell nanoparticles for super-resolution microscopy

   https://doi.org/10.1039/c9ra10421f  

   Thompson, S.; Pappas, Dimitri (February 2020, RSC Advances)

   Dye-doped nanoparticles have been investigated as bright, luminescent labels for super-resolution microscopy via localization methods. One key factor in super-resolution is the size of the luminescent label, which in some cases results in a frame shift between the label target and the label itself. Ag@SiO 2 core–shell nanoparticles, doped with organic fluorophores, have shown promise as super-resolution labels. One key aspect of these nanoparticles is that they blink under certain conditions, allowing super-resolution localization with a single excitation source in aqueous solution. In this work, we investigated the effects of both the Ag core and the silica (SiO 2 ) shell on the self-blinking properties of these nanoparticles. Both core size and shell thickness were manipulated by altering the reaction time to determine core and shell effects on photoblinking. Size and shell thickness were investigated individually under both dry and hydrated conditions and were then doped with a 1 mM solution of Rhodamine 110 for analysis. We observed that the cores themselves are weakly luminescent and are responsible for the blinking observed in the fully-synthesized metal-enhanced fluorescence nanoparticles. There was no statistically significant difference in photoblinking behavior—both intensity and duty cycle—with decreasing core size. This observation was used to synthesize smaller nanoparticles ranging from approximately 93 nm to 110 nm as measured using dynamic light scattering. The blinking particles were localized via super-resolution microscopy and show single particle self-blinking behavior. As the core size did not impact blinking performance or intensity, the nanoparticles can instead be tuned for optimal size without sacrificing luminescence properties. 

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5. Effect of metallic substrates and cavities on emission kinetics of dye-doped polymeric films

   https://doi.org/10.1364/JOSAB.409998  

   Koutsares, S.; Petrosyan, L_S; Prayakarao, S.; Courtwright, D.; Bonner, C_E; Shahbazyan, T_V; Noginov, M_A (December 2020, Journal of the Optical Society of America B)

   We have studied emission kinetics in dye-doped polymeric films (HITC:PMMA), deposited on top of glass and silver and embedded in Fabry–Perot cavities (metal-insulator-metal waveguides). For highly doped films on glass, we observed strong concentration quenching, as evidenced by a dramatic shortening of the emission kinetics, consistent with our previous studies. However, for the same dye-doped films on top of silver, slower emission kinetics were observed despite the high decay rates of individual dye molecules near the metallic surface. The concentration quenching rates in Fabry–Perot cavities were nearly identical to those of HITC:PMMA films deposited on top of silver. These findings are explained within a theoretical model for the inhibition of Förster energy transfer near a metallic surface. Furthermore, the emission kinetics of the dye-doped films on top of silver were approximately single exponential—consistent with the strong coupling of excited molecules with propagating surface plasmons. 

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