Fine Determination of Monoclinic Phase in Zirconia-Based Implants: A Surface-Enhanced Raman Spectroscopy (SERS) Study

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, which is attributed to the observed transformation of its crystalline structure from tetragonal to monoclinic phase. The presence of monoclinic phases, therefore, is a red-flag for the impending catastrophic breakdown of its mechanical properties. In this work, we utilize surface-enhanced Raman spectroscopy (SERS) with colloidal gold nanostars with mean diameter of 78 +/- 13 nm (measured from tip to tip across the nanostar) as substrate. The nanostars have localized surface plasmon resonance at 690 nm. Spectral maps on clean and nanostar-covered surfaces were obtained exactly at the same position using con focal Raman spectroscopy. Comparison of the two maps shows that there are more monoclinic phases detected in the nanostar-covered surface possibly due to the "lightning rod" effect in the nanostar tips. SERS of solid zirconia has not been demonstrated elsewhere and our results could provide early evidence of the effectivity of the technique even on non-porous materials. With further improvement in sensitivity, SERS can be a promising technique for the early detection of monoclinic phase in zirconia-based implants.