Largely Enhanced Single-Molecule Fluorescence in Plasmonic Nanogaps Formed by Hybrid Silver Nanostructures

It has been suggested that narrow gaps between metallic nanostructures can be practical for producing large field enhancement. We design a hybrid silver nanostructure geometry in which fluorescent emitters are sandwiched between silver nanoparticles and silver island film (SIF). A desired number of polyelectrolyte layers are deposited on the SIF surface before the self-assembly of a second silver nanoparticle layer. Layer-by-layer configuration provides a well-defined dye position. It allows us to study the photophyical behaviors of fluorophores in the resulting gap at the single molecule level. The enhancement factor of a fluorophore located in the gap is much higher than those on silver surfaces alone and on glass. These effects may be used for increased detectability of single molecules bound to surfaces which contain metallic structures for either biophysical studies or high sensitivity assays

Schematic diagram of a coupled side-view μPIV system (not to scale).

<p>A) The flow chamber was constructed by two microslides with a smaller one being inserted into a bigger one, and two 45° mirrors coated with a high-reflected layer placed on each side of the chamber. The light path for a top-view (lower) and a side-view (upper) is illustrated <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030721#pone.0030721-Cao1" target="_blank">[58]</a>. B) μPIV components include a double-pulse Nd: YAG laser, a camera, a synchronizer, an amplifier and other optical components, as well as a microscope with fluorescent cubes and an objective lens. It also shows an optical path for a side-view μPIV imaging.</p

Upstream velocity profile (solid circle •) and velocity profile above a cell (open circle ○) were overlapped.

<p>Upstream velocity profile (solid circle •) and velocity profile above a cell (open circle ○) were overlapped.</p

Association between sex and efficacy of immune checkpoint inhibitors: a systematic review and meta-analysis

PRISMA checklistSupplementary data</p

Velocity profile above an adherent PMN (open circle ○), above a TC (open triangle Δ) and the upstream (solid diamond ⧫).

<p>Velocity profile above an adherent PMN (open circle ○), above a TC (open triangle Δ) and the upstream (solid diamond ⧫).</p

Velocity profile in side-view flow chamber measured by μPIV.

<p>The dimension for a side-view flow chamber is 550 µm high and 700 µm wide. Images were captured only in the middle 1/3 region across the width. A) X-velocity calculated from images taken by a 10× objective lens was plotted with respect to distance from the center of chamber showing a parabolic curve pattern. B) X-velocity calculated from images taken by a 40× objective lens was plotted with respect to distance from substrate and showed a linear curve pattern.</p

Reynolds number calculated from μPIV results.

<p>Reynolds number calculated from μPIV results.</p

CFD simulations.

<p>X-velocity profile was plotted with respect to the distance away from the cell surface on the top, for all five relative PMN-to-TC position states, under both low shear (73 µl min⁻¹) and high shear (365 µl min⁻¹). A) Above an adherent PMN under low shear condition; B) Above an adherent TC under low shear condition; C) Above an adherent PMN under high shear condition; D) Above an adherent TC under high shear condition. Various symbols represent the position state of a TC approaching a PMN (□); a TC colliding with a PMN (○); a TC forming a transient aggregate with a PMN (△); a TC firmly adhering to a PMN (▪); and a TC detaching from a PMN (•), respectively.</p

Local shear rates above adherent cells calculated from μPIV results.

<p>Local shear rates above adherent cells calculated from μPIV results.</p

Relative Shear Rates above two adherent cells for different PMN-to-TC position states.

<p>A) Above an adherent PMN (including a single PMN without a TC); B) Above an adherent TC (no data for a transient aggregate state as the TC was not in the same plane as a PMN).</p