Blinking in surface-enhanced Raman spectrum beyond a single molecule

Intermittent emission is a special characteristic of single molecule fluorescence, which is also called fluorescence blinking [Nature (London) 388, 355 (1997), Science 277, 1074 (1997)] and has also been observed in 0D [Nature (London) 383, 802 (1996)], 1D [Nat. Phys. 4, 519 (2008)] and 2D materials [Nature (London) 541, 62 (2017)]. The surface enhanced Raman spectrum (SERS) of a single molecule also shows blinking, which is commonly attributed to the movement of the molecule in and out of the active site of the metal nanoparticle [Science 275, 1102 (1997)]. For bulk samples, it is reasonable that no fluorescence or Raman blinking can be observed due to ensemble averaging from numerous molecules. In this work, however, we observed SERS blinking of bulk samples around a single gold nanorod (GNR) in solid matrices. Such SERS blinking behavior can be observed for different samples once the GNR is excited resonantly. These results suggest an intriguing mechanism of SERS blinking that does not require a single molecule. We propose two possible mechanisms that can explain the experimental results and suggest reconsidering the physical picture of the SERS blinking behaviors in both ensemble and single-molecule measurements.