Noble metal-free SERS: mechanisms and applications

Abstract

Surface-enhanced Raman scattering (SERS) is a very important tool in vibrational spectroscopy.

Toward Modeling the Complexity of the Chemical Mechanism in SERS

“…Plasmonic substrates are primarily used in SERS due to the large EM enhancement, which makes it difficult to study the CM enhancement. Alternatively, using nonplasmonic substrates can effectively eliminate the EM, thereby leaving only the CM. ,− Organic semiconductors, , metal–organic frameworks (MOFs), , perovskite nanocrystals, , copper telluride nanoparticles and also 2D materials, such as transition metal dichalcogenides − along with graphene ,− and its derivatives, have emerged as SERS substrates. The variety of these nonplasmonic SERS substrates provides an experimental platform for studying CM.…”

“…For nonplasmonic substrates, the CT mechanism is often invoked to explain the enhancement. This is due to the emergence of charge-transfer excitations in the interface between molecules and nonplasmonic substrates. ,, For example, in semiconductor substrates, charge-transfer excitations from substrate valence band (VB) to molecular LUMO or from molecular HOMO to substrate conduction band (CB) arise. , The CT enhancement is determined by the molecular orbital (MO) alignment relative to the substrate energy band − and can be tuned by controlling their relative alignment. Consequently, the optimal energy level alignment to achieve a large enhancement is that the energy difference is in resonance with the incident light.…”

Aptamer-aided plasmonic nano-urchins for reporter-free surface-enhanced Raman spectroscopy analysis of cortisol

“…To date, diverse nanomaterials are explored as the SERS substrates for signal improvement. 21,22 Experientially, the enhancement of SERS efficacy can be achieved by creating hot spots through nanoparticles that are close together (usually around 1–5 nm apart). 23,24 Moreover, hot spots can be produced at areas such as tips, edges, or crevices of the interface.…”

A highly simple and controllable nitrogen-doping method for carbon-based surface-enhanced Raman spectroscopy substrates

“…1–6 While traditional SERS substrates primarily consist of metal-based materials, distinguished by significant enhancement factors (EFs) and devoid of inherent SERS signals, 1–13 there has been a substantial shift toward exploring efficient metal-free alternatives, particularly those made from carbon-based materials. 14–38 Such metal-free substrates enhance the Raman signal by forming a charge-transfer (CT) complex between the analyte and the substrate. This interaction modifies the electronic energy levels and amplifies the Raman signal via the resonance Raman effect, a process known as the “chemical enhancement mechanism”.…”