Plasmonic porous ceramics for molecule detection via surface-enhanced Raman scattering

A plasmonic porous ceramic can be defined as a three-dimensional porous ceramic matrix
with embedded plasmonic nanoparticles. Like regular ceramics, this material class shows
advantages like high temperature and pressure stability, chemically inertness, along with
dielectric properties. Plasmonic porous ceramics have a high potential for a broad range of
applications in various fields, for example ultrasensitive chemical detection under high temperature/high-pressure conditions, for biomarker detection in biological systems or for
highly efficient energy generation through plasmonic photothermal heating.
In general, plasmonic materials are developed because of their ability of confining and
manipulating electromagnetic radiation, which enables highly sensitive and rapid detection of
molecules, for example via surface-enhanced Raman spectroscopy (SERS). Typical
plasmonic nanoparticles used for SERS are gold and silver nanoparticles. Because of the high
density of mobile electrons, plasmonic nanoparticles (Au, Ag nanoparticles) can couple with
the electromagnetic radiation of wavelengths that are far larger than the nanoparticles
themselves. Light absorption and scattering by plasmonic nanoparticles can be tailored by
varying their size, geometry and relative positions.
This thesis aims to present the new concept of plasmonic porous ceramic by introducing
plasmonic nanostructures in open-cell foam ceramics and to investigate application
possibilities of this substrate due to its advanced optical properties. These optical properties
of the plasmonic porous ceramic lead to significant magnification of the Raman scattering
signal, that enables this substrate serving as SERS substrate and providing molecule
“fingerprint” for sensitive and real-time detection.
Therefore, the first cornerstone of this work is proof-of-principle of plasmonic porous ceramics.
Open porous ceramic structures based on zirconia-toughened alumina (ZTA) were processed,
sintered and functionalized with silver nanoparticles. The Raman enhancement of the
plasmonic structures was analyzed as a function of the amount of deposited silver
nanoparticles, pore diameter and strut diameter of the ceramic structure using the probe
molecule pyridine. Flat substrates of the same chemical composition and non-porous
fragments of the porous structure were used for comparison. The Raman signal is found to be
significantly augmented by the porous structure compared to that collected on flat substrates
with similar composition. Accordingly, the plasmonic porous ceramics were supposed to be
well suited as 3D SERS substrates, allowing real-time Raman sensing of trace amounts of
molecules.