Metal-free SERS: Where we are now, where we are heading

Abstract

In recent years, the emergence of metal-free surface-enhanced Raman scattering (SERS) substrates has provided promising alternatives for reliable, high-sensitivity Raman spectroscopy due to their potential to realize highly tuneable, biocompatible, and reproducible Raman enhancement. In this perspectives article, we discuss recent developments and anticipate new opportunities for metal-free SERS. Specifically, we review the theory of metal-free SERS, including electromagnetic enhancement and chemical enhancement, and introduce promising substrates developed recently, including MXenes, transition metal dichalcogenides, and carbon-based substrates. Moreover, we clarify challenges, provide potential solutions, and discuss unexploited applications. This perspective provides not only a broad and detailed view of metal-free SERS at the current stage, but also a roadmap for its future advancement.

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

“…These chemical groups, characterized by polar structures, induce dipole–dipole interactions between the substrate and R6G or CV. 17 Therefore, a balance between the expansion of the conjugated system and the inclusion of graphitic N in substrates may contribute considerably to observing strong SERS effect.…”

“…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”.…”

Substrate types and applications of MXene for surface-enhanced Raman spectroscopy

“…MXene has many potential applications among 2D materials due to its excellent SERS activity, biocompatibility, and environmental friendliness ( Chen et al, 2020 ). Owing to the outstanding advantages of SERS, such as high sensitivity, high stability, and narrow spectral bandwidth, SERS detection based on MXene could be used in many scenes in production and life ( Martinez Pancorbo et al, 2021 ; Tyagi et al, 2023 ).…”

Deciphering the Potential of Multidimensional Carbon Materials for Surface-Enhanced Raman Spectroscopy through Density Functional Theory

“…To address the limitations associated with noble metal-based SERS, researchers have turned to nonmetallic SERS substrates, including graphene, functional semiconductors such as Cu 2 O, MoS 2 , and Al 2 O 3 , metal atom-doped carbon materials, − and three-dimensional spatial carbon nanomaterials . These substrates employ a chemical mechanism (CM) for achieving significant Raman enhancement, which includes nonresonant chemical enhancement (improvement of polarizability for the probe molecule through chemical interaction) and resonant chemical enhancement [based on charge-transfer (CT) excitation].…”