RAMAN AND FLUORESCENCE SPECTROSCOPY OF BIOMEDICAL NANOMATERIALS
Vega, Marienette Morales
Stabilized zirconia exhibits unsurpassed mechanical properties and biocompatibility, making it an indispensable ceramic material for biomedical implants. One of the most problematic features of stabilized zirconia has been its low-temperature degradation(LTD), which is associated to the observed transformation of its crystalline structure from tetragonal to monoclinic phase. The presence of monoclinic phases, therefore, is the red-flag for the impending catastrophic breakdown of mechanical properties. In this work, we establish characterization protocols to extend the sensitivity limit of conventional Raman spectroscopy for determination of extremely little amounts of monoclinic phase in zirconia implant prototypes. We accomplish this in two ways. First, we employ Raman spectroscopy and multivariate statistical analysis on a series of fully-dense and partially transformed Y-TZP zironia prototypes. Incipient t-m transformation is only revealed with high resolution spectral mapping and principal component analysis. The technique reveals the presence of islands of monoclinic phase that are otherwise not visible by simple observation and fitting of individual spectra. High resolution mapping likewise allows for probing homogenieties in the sample, which is a critical component in the development of implants. The second protocol utilizes surface-enhanced Raman spectroscopy (SERS) with colloidal gold nanostars as substrate. The nanostars used have localized surface plasmon resonance (LSPR) at 690 nm. Two spectral maps, on clean and on nanostars-covered surface, were obtained exactly at the same position using confocal Raman spectroscopy. Comparison of the two maps shows that there are more monoclinic phases detected in the nanostars-covered surface possibly due to the “lightning rod” effect in the nanostar tips. We report an unprecedented attempt on SERS on solid zirconia, which provides early evidence of the effectivity of the technique even on non-porous materials. With further improvement in sensitivity, SERS is a promising technique for the early detection of monoclinic phase in zirconia-based implants.