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

Abstract

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.