Toward Graphene‐Enhanced Spectroelectrochemical Sensors

Abstract

The SERS effect arises mainly from electromagnetic (EM) and chemical (CM) enhancement of the Raman signal. [3] The EM enhancement is on the order of ≈|E| 4 , amplifying signals >10 8 , where E is the intensity of the EM field. On the other hand, CM enhancement has been shown to enhance the signal ≈10-100×. Nevertheless, SERS enhancement is contingent on the quality of the substrate. Preparation of a suitable substrate requires rigorous micro/nanofabrication processes, such as electrochemical or high vacuum deposition of noble metals (e.g., Ag, Au, Cu) or the selfassembly of size-controlled colloidal noble metal nanoparticles, which are very complex, contaminated, and not homogenous, leading to a lowered SERS effect. Moreover, when metal-based rough substrates, such as Ag or Cu, are used for SERS, they tend to oxidize, which prevents their use in some applications. Additionally, noble metals have relatively poor biological compatibility, hindering their use in biomedical applications.Recently, graphene-enhanced Raman spectroscopy (GERS) has emerged as a novel technique where graphene-based ultra-smooth substrates exhibit strong Raman enhancement from adsorbed molecules. [4][5][6] Graphene is cheap, easy to produce, and remains stable even in relatively harsh conditions. The flat and chemically inert surface and environmentally friendly nature of graphene make it compatible for widespread use including biosensing, biomedical, and environmental applications. [7][8][9] The GERS technique is associated with the CM enhancement mechanism, where the charge transfer occurs between adsorbed molecules and the substrate. [4,10] As the surface plasmon on graphene is in the terahertz range rather than the visible range, graphene does not support EM enhancement by the excitation of visible energy photons. [11] Chemical mechanism-initiated GERS facilitates molecular selectivity, enhancing the charge transfer between the molecules and the graphene. The high stability and reproducibility of the Raman enhanced spectra from graphene makes GERS more suitable for applications than SERS. [12] It has been previously reported that the enhancement from GERS on nitrogen-doped graphene was about ten times higher than SERS with the same probe molecules, while for pristine graphene, it was five times higher. [13] Different molecules have been probed with GERS, making it an effective approach for sensing. [14,15] Theoretical and experimental studies have been conducted to obtain more insight into the mechanism

Recent advances in graphene-based electroanalytical devices for healthcare applications

“…7D (iii)) graphene in devising GR-enhanced spectro-electrochemical sensors (GE-SPECSs). 195 Their studies revealed that hole-doped h-graphene exhibited superior GERS signals compared to pgraphene, achieving a LOD of around 10 −7 M. By capitalizing on the adjustable work function of graphene, they demonstrated the ability to modulate the GERS signal and probe various oxidation states of molecules through the application of appropriate external potentials (Fig. 7D (i)).…”

Large‐Area Mechanically‐Exfoliated Two‐Dimensional Materials on Arbitrary Substrates

“…[ 2–8 ] Due to the aforementioned properties and extreme sensitivity to the environment, monolayers of layered materials can be used in wide ranging applications such as ultra‐high performance optoelectronics, sensors, flexible electronics, energy conversion and storage, biomedicine, and defense. [ 9–15 ]…”

“…[2][3][4][5][6][7][8] Due to the aforementioned properties and extreme sensitivity to the environment, monolayers of layered materials can be used in wide ranging applications such as ultra-high performance optoelectronics, sensors, flexible electronics, energy conversion and storage, biomedicine, and defense. [9][10][11][12][13][14][15] At a laboratory level, preparation of monolayers (1L) of 2D materials is straightforward as small individual flakes on the order of tens of μm in lateral size usually suffice. However, the utility of 2D materials at an industrial level is still limited by the conflicting relation between the size and quality of 1L flakes.…”