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Tip-enhanced spectroscopy and its Raman variant, tip-enhanced Raman spectroscopy (TERS), provide the possibility to spatially resolve the vibrations of a single molecule when combined with ultra-high vacuum technology, but this technique suffers from poor time resolution2,3. On the other hand, surface-enhanced Raman spectroscopy (SERS) is a more common technique, and is used for many imaging and bioanalytical applications, still with single molecule sensitivity but, unlike TERS, without spatially resolved molecular imaging capabilities4. In SERS, the roughness and geometric characteristics of metallic surfaces (in general Al, Ag or Au) are exploited to enable high spatial confinement of an impinging electromagnetic field. Since the SERS signal scales with the square power of the electromagnetic fields of both excitation and Raman shift, even a small increase of the local field creates so-called hot spots that yield large Raman intensity. Yet, for low concentrations of analytes deposited onto these surfaces, the collected SERS signal fluctuates with time, and the cause of such signal variation is assigned to the chemical stability of the metal–adsorbate interaction, the dynamics of the molecules in extremely confined fields and the transient nature of the hot spots.
Citation of this paper:
McRae, D.M., Lagugné-Labarthet, F. In search of the hot spot. Nat. Nanotechnol. 14, 922–923 (2019). https://doi.org/10.1038/s41565-019-0540-9