Ultra-High-Speed Dynamics in Surface-Enhanced Raman Scattering

Abstract

In this perspective, we discuss recent observations related to the temporal dynamics of intensities in surface-enhanced Raman scattering (SERS) experiments. SERS is a well-established and highly active research field, driven by the potential of the technique in analytical and bioanalytical applications. However, there are several fundamental aspects of the effect that still challenge and fascinate researchers in the area. Here we will focus on the recent observation that strong SERS intensity fluctuations (SIFs) are seen when experiments are performed at fast acquisition rates, even when the metal surface is completely covered by an adsorbate. Interestingly, the SIF dynamics indicate bursts of SERS activities that last only a few hundreds of microseconds, followed by a longer period of inactivity. This type of behavior has been observed from several systems and configurations, including single metallic nanoshells and nanostars, immobilized colloidal aggregates, nanoparticle-on-a-mirror configurations, and metal-coated microspheres. This diversity suggests that the dynamical behavior is a fundamental characteristic of the SERS effect. Time-dependent atomic rearrangements within the confined environment of the SERS hotspots are suggested as the main mechanism driving these fluctuations. The dynamical SERS behavior, revealed with high-speed acquisitions, should provide a new direction for the study of atomic reconstruction and single molecule interactions with metallic nanoenvironments with an unprecedented level of detail.

Investigating the Performances of Wide-Field Raman Microscopy with Stochastic Optical Reconstruction Post-Processing

“…Coupling label-free Raman imaging with stochastic microscopy is a potential alternative for chemical fingerprint imaging. 21,28 The dynamic nature of the hotspot generation produces time-dependent SERS signal 29–33 that can be further exploited for STORM processing. However, using SERS for wide-field imaging requires a uniform and dense distribution of hotspots which is difficult to achieve experimentally.…”

“…34 In the case of conductive or semi-conductive surface, the fluctuations can also arise from the generation and rearrangements of local hot-spots within picocavities. 33,35 Signal fluctuations may also come from thermal effect and laser intensity fluctuations. In wide-field illumination, the probability of inducing vibrational transition and Raman scattering for each point of the sample can differ depending on the absorption of light.…”

DNA Structure-Stabilized Liquid–Liquid Self-Assembled Ordered Au Nanoparticle Interface for Sensitive Detection of MiRNA 155

“…10−12 Among them, the bottom-up self-assembly method of nanomaterials on water−oil interface is proven to solve the random aggregation of nanoparticles on solid surfaces efficiently. 13−15 The self-assembly interface of nanomaterials is ordered at the two-phase interface by the combination of multiple forces, 16,17 such as capillary force, van der Waals force, space electrostatic repulsion, and solvation tension. 18 Fur-thermore, SERS detection at liquid-phase self-assembly interfaces not only maintains the activity of biomolecules but also enables Raman molecules in solution to bind more rapidly and tightly in the "hot spot" region (high localized electromagnetic field).…”

“…Gold (or silver) nanomaterials are commonly used as SERS substrates because they can produce strong localized surface plasmon resonance (LSPR) effects and their good biocompatibility. , However, the uncontrollable factors of aggregation, homogeneity, and coffee-ring effect , of the nanomaterials on solid-phase substrates led to poor reproducibility and stability of SERS quantitative detection. Researchers have explored different solutions such as using a template, etching method, and self-assembled vesicles to produce uniform Au and Ag substrates. − Among them, the bottom-up self-assembly method of nanomaterials on water–oil interface is proven to solve the random aggregation of nanoparticles on solid surfaces efficiently. − The self-assembly interface of nanomaterials is ordered at the two-phase interface by the combination of multiple forces, , such as capillary force, van der Waals force, space electrostatic repulsion, and solvation tension . Furthermore, SERS detection at liquid-phase self-assembly interfaces not only maintains the activity of biomolecules but also enables Raman molecules in solution to bind more rapidly and tightly in the “hot spot” region (high localized electromagnetic field). , Recently, the self-assembled Au nanoparticle (Au NPs) interface on the liquid phase is applied in food safety and bioassays. − However, the self-assembled Au NP interface produces cracks or even disappears due to shaking or shifting when the forces are unbalanced, and the Brownian motion of solution may cause instability.…”

Wide-field Surface-Enhanced Coherent Anti-Stokes Raman Scattering Microscopy

“…[3][4] However, most of the instrumentations used for SERS imaging are equipped with a CCD detector which typically operates with acquisition rate on the order of 1 Hz and rely on the mechanical scanning process. [5] For large-area imaging, the time-consuming point-bypoint scanning process with an acquisition time of few seconds often takes minutes to hours for mapping the SERS spectra of a sample. [6] With high-speed cameras and tunable filters, wide-field SERS imaging has been developed to meet the need for large-scale Raman imaging.…”