Recent advancements in metal-enhanced fluorescence (MEF) suggest that it
can be a promising tool for detecting molecules at very low concentrations
when a fluorophore is fixed near the surface of metal nanoparticles. We report
a simple method for aggregating multiple gold nanoparticles (GNPs) on
Rhodamine B (RhB)-doped silica nanoparticles (SiNPs) utilizing
dithiocarbamate (DTC) chemistry to produce MEF in solution. Dye was
covalently incorporated into the growing silica framework via co-condensation
of a 3-aminopropyltriethoxysilane (APTES) coupled RhB precursor using the
Stöber method. Electron microscopy imaging revealed that these mainly non spherical particles were relatively large (80 nm on average) and not well
defined. Spherical core-shell particles were prepared by physisorbing a layer
of RhB around a small spherical silica particle (13 nm) before condensing an
outer layer of silica onto the surface. The core-shell method produced
nanospheres (~30 nm) that were well defined and monodispersed. Both dye doped SiNPs were functionalized with pendant amines that readily reacted
with carbon disulfide (CS2) under basic conditions to produce DTC ligands
that have exhibited a high affinity for gold surfaces. GNPs were produced via
citrate reduction method and the resulting 13 nm gold nanospheres were then
recoated with an ether-terminated alkanethiol to provide stability in ethanol.
Fluorescent enhancement was observed when excess GNPs were added to
DTC coated dye-doped SiNPs to form nanoparticle aggregates. Optimization
of this system gave a fluorescence brightness enhancement of over 200 fold.
Samples that gave fluorescence enhancement were characterized through
Transmission Emission Micrograph (TEM) to reveal a pattern of multiple
aggregation of GNPs on the dye-doped SiNPs.
