Surface plasmon-coupled
emission (SPCE) has emerged as an interdisciplinary,
versatile sensing platform because of its highly directional, solid-state,
and polarized emission. Here, we report the distinct properties rendered
by silver Soret colloids (Ag-SCs) such as nanovoids and nanocavities
to observe 104-fold enhancement in the emission intensity of omnidirectionally
radiating emitter dipoles. Unlike earlier reports utilizing templated
silver nanoparticles (AgNPs) in spacer or cavity architectures, here
we employ template-free, linker-less Ag-SCs. The Purcell factor (maximum
of 120.6) obtained using the finite-difference time-domain simulations
for Soret nanocavities is in excellent agreement with the trend in
emission enhancements obtained experimentally. The thermal gradient
created by adiabatic cooling of AgNPs drives their thermodiffusion,
resulting in monodisperse nanoparticle assemblies (Ag-SCs). In addition,
we report an extended-cavity architecture with Ag-SCs, as a novel
pseudo-metal–dielectric–metal (MDM) interface, for achieving
80-fold SPCE. This study also features the unique properties of Ag-SCs
as interfacial nanomaterials on the SPCE platform to achieve femtomolar
detection of glutathione (GSH). The quenching of fluorescence from
the Alizarin Red S–boric acid (ARS–BA) complex upon
the addition of Cu2+ ions and the dequenching upon the
GSH addition studied with Ag-SCs as the spacer layer remarkably increased
the sensitivity of the analyte. The uniform and intense electromagnetic-field
confinement provided by these intricate architectures and hybrid interfaces,
along with their ease of fabrication and versatility for a variety
of analytes, is critical to achieving augmented SPCE. This is accomplished
without compromising the reliability of detection, as demonstrated
with the use of a cellphone camera, Commission Internationale de l’Eclairage
color space, and luminosity plots for turn-on fluorescence. The emission
images were acquired using an android-phone camera by aligning it
with its angular emission, making it amenable for point-of-care diagnostics.
We report cellphone-based detection of dopamine with attomolar sensitivity in clinical samples with the use of a surface plasmon-coupled emission (SPCE) platform. To this end, silver-coated carbon nanotubes were used as spacer and cavity materials on SPCE substrates to obtain up to 100-fold fluorescence enhancements. The presence of silver on the carbon nanotubes helped to overcome fluorescence quenching arising due to π-π interactions between the carbon nanotube and rhodamine 6G. The competing adsorption of dopamine versus rhodamine 6G on graphene oxide was utilized to develop this sensing platform.
We have engineered the use of 2D, 1D and 0D carbon allotropes as spacers to achieve in excess of 1000-fold fluorescence enhancements in a Surface plasmon-coupled emission (SPCE) platform. We also have demonstrated the femtomolar sensitivity of silver decorated carbon dots (AgCD) in the detection of a radiating dipole.
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