Tabitha Jones1,Tung Chun Lee1
University College London1
Tabitha Jones1,Tung Chun Lee1
University College London1
Hybrid nanomaterials of plasmonic metals and semiconductors have been the focus of growing research in surface-enhanced Raman spectroscopy (SERS).[1] Significant increase in SERS signals can be achieved by harnessing additional chemical enhancements which occur due to photo-induced charge transfer between a plasmonic metal and a semiconductor. A notable example is photo-induced enhanced Raman Scattering (PIERS), where additional boost of SERS signals can be achieved via UV-light irradiation that creates oxygen vacancies and consequently activates the chemical enhancement.[2] Recently, our group demonstrated the first UV-irradiation-free PIERS effect by employing nanoscale coatings of SnO<sub>2</sub> that are intrinsically rich in oxygen vacancies.[3]<br/><br/>Here, we present a new and unusual SERS phenomenon.[4] Colloidal Ag@SnO<sub>2</sub> core@shell nanoparticles (NPs) were synthesised and fabricated into a compact layer of solid substrate. When SERS measurements were performed, the signal showed a significant and irreversible increase over time (up to 25-fold enhancement after an hour). We name this effect dynamic-SERS (d-SERS). While not observed for uncoated Ag NPs, d-SERS results in much larger signals than conventional SERS (by more than 1 order of magnitude) and reveals target-specific dynamic information. We performed d-SERS measurements for a range of clinically relevant analytes, including uric acid and ketamine, achieving sub-mM limit of detection. Notably, the rate of increase of the characteristic SERS peaks can be used for quantitative detection of these analytes, showing improved reliability of the measurement by reducing the signal variability due to non-uniform substrate morphologies.<br/><br/>In attempt to elucidate the underlying mechanism of d-SERS, we performed X-ray photoelectron spectroscopy (XPS) and studies on laser powers and external heating. We propose that the enhancement is due to plasmonic heating of the Ag NPs, which generates additional oxygen vacancies in the SnO<sub>2 </sub>enabling charge transfer and boosting the chemical enhancement component of SERS. This work opens up new possibilities for plasmonic metal-semiconductor hybrid SERS and paves the way for improved detection of a range of analytes, with applications in healthcare, security and environmental monitoring.<br/><br/>[1] Langer, J. <i>et al.</i> <i>ACS Nano,</i> <b>2019</b>, 14, 1, 28-117<br/>[2] Ben-Jaber, S. <i>et al.</i> <i>Nat Commun.,</i> <b>2016</b>, 7, 12189<br/>[3] Davison, G. <i>et al.</i> <b>2022 </b>[Manuscript submitted for publication]<br/>[4] Jones, T. <i>et al.</i> <b>2022 </b>[Manuscript in preparation]