Lighting Up the Raman Signal of Molecules in the Vicinity of Graphene Related Materials

Abstract

Surface enhanced Raman scattering (SERS) is a popular technique to detect the molecules with high selectivity and sensitivity. It has been developed for 40 years, and many reviews have been published to summarize the progress in SERS. Nevertheless, how to make the SERS signals repeatable and quantitative and how to have deeper understanding of the chemical enhancement mechanism are two big challenges. A strategy to target these issues is to develop a Raman enhancement substrate that is flat and nonmetal to replace the conventional rough and metal SERS substrate. At the same time, the newly developed substrate should have a strong interaction with the adsorbate molecules to guarantee strong chemical enhancement. The flatness of the surface allows better control of the molecular distribution and configuration, while the nonmetal surface avoids disturbance of the electromagnetic mechanism. Recently, graphene and other two-dimensional (2D) materials, which have an ideal flat surface and strong chemical interaction with plenty of organic molecules, were developed to be used as Raman enhancement substrates, which can light up the Raman signals of the molecules, and these substrates were demonstrated to be a promising for microspecies or trace species detection. This effect was named "graphene enhanced Raman scattering (GERS)". The GERS technique offers significant advantages for studying molecular vibrations due to the ultraflat and chemically inert 2D surfaces, which are newly available, especially in developing a quantitative and repeatable signal enhancement technique, complementary to SERS. Moreover, GERS is a chemical mechanism dominated effect, which offers a valuable model to study the details of the chemical mechanism. In this Account, we summarize the systematic studies exploring the character of GERS. In addition, as a practical technique, the combination of GERS with a metal substrate incorporates the advantages from both conventional SERS and GERS. The introduction of graphene to the Raman enhancement substrate extended SERS applications in a more controllable and quantitative way. Looking to the future, we expect the combination of the SERS concept with the GERS technology to lead to the solution of some important issues in chemical dynamics and in biological processes monitoring.

Gold Nanoparticle Coated Carbon Nanotube Ring with Enhanced Raman Scattering and Photothermal Conversion Property for Theranostic Applications

“…1–3 The spectrometric sensor based on the surface enhanced Raman scattering (SERS) signal of carbon nanotube (CNT) and graphene was also developed to detect biomolecules, such as DNA, RNA, protein, and so on. 4–7 To further increase their SERS signal, hybrid nanomaterials of sandwiched gold-CNT/reduced graphene oxide (rGO)–gold were recently exploited to investigate their electrostatic interactions.…”

Molecular sensitivity of metal nanoparticles decorated graphene‐family nanomaterials as surface‐enhanced Raman scattering (SERS) platforms

“…Graphene‐decorated with metal nanocrystals are attracting a great deal of attention. For instance, the inclusion of metal (Fe, Gd, and Al), alkali metal (Li, Na, and K), and coinage metal nanoparticles (Cu, Ag, and Au) onto GFNs result in SERS, better electrocatalytic activity, increased sensitivity, and specificity in chemical, electrochemical sensing, and DNA detection . The GFNs are proposed for Raman enhancement, termed as graphene‐mediated surface‐enhanced Raman scattering (G‐SERS) in comparison with other substrates .…”

Raman excitation profiles of hybrid systems constituted by single‐layer graphene and free base phthalocyanine: Manifestations of two mechanisms of graphene‐enhanced Raman scattering

“…The ability of graphene to enhance Raman scattering of molecules located on graphene surfaces in hybrid systems was first reported in 2010 and denoted graphene‐enhanced Raman scattering (GERS) . Recently, the six years of activity in this research field have been reviewed . The magnitude of the GERS enhancement has been found to depend on several factors, such as the structure and symmetry of a molecule, energy of its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), molecule–graphene distance, graphene sample thickness, graphene Fermi level energy and laser excitation wavelength.…”

“…The magnitude of the GERS enhancement has been found to depend on several factors, such as the structure and symmetry of a molecule, energy of its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), molecule–graphene distance, graphene sample thickness, graphene Fermi level energy and laser excitation wavelength. About 30 different molecules have already been probed for GERS, and the best results have been obtained for planar aromatic molecules and single‐layer graphene (SLG) . The average GERS enhancement factor values were found to be in the 2–15 range (for planar molecules on SLG surface), while the largest GERS enhancement factor of 47 was achieved for CuPc (Pc = phthalocyanine) at 633‐nm excitation .…”