Surface-Enhanced Raman Scattering Using 2D Materials

The use of surface-enhanced Raman scattering (SERS) as a technique for detecting small amounts of (bio)chemical analytes has become increasingly popular in various fields. While gold and silver nanostructures have been extensively studied as SERS substrates, the availability of other types of substrates is currently expanding the applications of this spectroscopic method. Recently, researchers have begun exploring two-dimensional (2D) materials (e. g., graphene-like nanostructures) as substrates for SERS analysis. These materials offer unique optical properties, a well-defined structure, and the ability to modify their surface chemistry. As a contribution to advance this field, this concept article highlights the significance of understanding the chemical mechanism that underlies the experimental Raman spectra of chemisorbed molecules onto 2D materials' surfaces. Therefore, the article discusses recent advancements in fabricating substrates using 2D layered materials and the synergic effects of using their metallic composites for SERS applications. Additionally, it provides a new perspective on using Raman imaging in developing 2D materials as analytical platforms for Raman spectroscopy, an exciting emerging research area with significant potential.

Nanoarchitected graphene/copper oxide nanoparticles/MoS2 ternary thin films as highly efficient electrodes for aqueous sodium-ion batteries

Sodium-ion batteries (SIBs) operating in aqueous electrolyte are an emerging technology that promises to be safer, cheaper, more sustainable and more efficient than their lithium-based counterparts. One of the great challenges associated with this technology is the development of advanced materials with high specific capacity to be used as electrodes. Herein, we describe an ingenious strategy to prepare unprecedented tri-component nanoarchitected thin films with superior performance when applied as anodes in aqueous SIBs. Taking advantage of the broadness and versatility of the liquid-liquid interfacial route, three transparent nanocomposite films comprising graphene, molybdenum sulphide and copper oxide nanoparticles have been prepared. The samples were characterized using several techniques, and the results demonstrated that depending on the specific experimental strategy, different nanoarchitectures are achieved, resulting in different and improved properties. An astonishing capacity of 1377 mA h g-1 at 0.1 A g-1 and a degree of recovery of 100% were observed for the film in which the interactions among the components were optimized. This is among the highest capacity values reported in the literature and demonstrates the potential of these tri-component materials to be used as anodes in aqueous sodium-ion batteries.

Reduced graphene oxide nanosheets decorated with core-shell of Fe3O4-Au nanoparticles for rapid SERS detection and hyperthermia treatment of bacteria

In this study, the core-shell of Fe₃O₄-Au nanoparticles (NPs) were prepared by seeding AuNPs onto Fe₃O₄ NPs modified with poly-ethylenimine (PEI). Later, Fe₃O₄-Au NPs were attached to cationic poly(dimethyldiallylammonium chloride) (PDDA)-modified graphene oxide (GO) nanosheets through in situ self-assembly behaviors, termed as Fe₃O₄-Au@RGO nanocomposites, for surface-enhanced Raman scattering (SERS) detection and hyperthermia treatment of bacteria. The resulting Fe₃O₄-Au@RGO nanocomposites were evaluated systematically by transmission electron microscope, zeta potential, X-ray diffraction, X-ray photoelectron spectroscopy, and vibrating sample magnetometer. It revealed that the core-shell structured Fe₃O₄-Au NPs were dispersed homogeneously on the surface of the GO nanosheets. Furthermore, the rapid SERS detection for small biomolecules and bacteria was conducted by Raman spectroscopy. The results showed that the greatest SERS intensity was fne tuned at the weight ratio of Fe₃O₄-Au/RGO nanosheets was 20/1, displaying the optimal interparticle gap of AuNPs to induce the huge hot-spots effect. The magnetic inductive heating capability of Fe₃O₄-Au@RGO nanocomposites was produced under high frequency magnetic field exposure and can kill high than 90% of the bacteria at 10 min. Hence, the newly developed Fe₃O₄-Au@RGO nanocomposites were demonstrated to be viable for SERS detection of biomolecules and microbes and potential applications for magnetically capturing and hyperthermia treatment of bacteria.

Sonochemical synthesis of a copper reduced graphene oxide nanocomposite using honey and evaluation of its antibacterial and cytotoxic activities

The combination of graphene-based materials and inorganic nanoparticles for the enhancement of the nanomaterial properties is extensively explored nowadays. In the present work, we used a sonochemical method to synthesize a copper/reduced graphene oxide (Cu/RGO) nanocomposite using Australian honey and vitamin C as capping and reducing agents, respectively. The honey-mediated copper/reduced graphene oxide (H/Cu/RGO) nanocomposite was then characterized through UV-visible, XRD, HRTEM, and FTIR analysis. The copper nanoparticles (Cu-NPs) in the nanocomposite formed uniform spherical shapes with a size of 2.20 ± 0.70 nm, which attached to the reduced graphene oxide (RGO) layers. The nanocomposite could suppress bacterial growth in both types of bacteria strains. However, in this study, the nanocomposite exhibited good bactericidal activity toward the Gram-positive bacteria than the Gram-negative bacteria. It also showed a cytotoxic effect on the cancer colorectal cell line HCT11, even in low concentrations. These results suggested that the H/Cu/RGO nanocomposite can be a suitable component for biomedical applications.

Analytical control of Rhodamine B by SERS using reduced graphene decorated with copper selenide

A novel approach for the decoration of reduced graphene oxide with copper selenide (CuSe-rGO), using supercritical carbon dioxide (sc-CO₂) as a medium, was developed and proposed as a new substrate for surface-enhanced Raman spectroscopy (SERS) to determine Rhodamine B in chili powder. The synthesized materials graphene oxide (GO), reduced graphene oxide (rGO) and CuSe-rGO were characterized by Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). All SERS spectra were obtained by using a portable Raman spectrometer. The procedure presented involves a simple and rapid sample pretreatment in order to determine Rhodamine B in chili powder, with a limit of quantification of 44.5 ng g^-1. The recovery values of the proposed method resulted in the 96% to 99% range, with RSD values from 2.4% to 3.0%. The developed SERS active hybrid substrate has an enhancement factor higher than those using gold or silver nanoparticles, providing a clear improvement in the sensitivity.

Graphene-based nanoplatforms for surface-enhanced Raman scattering sensing

Surface-enhanced Raman scattering (SERS) is one of the important techniques for sensing applications in biological analysis, disease diagnosis, environmental science, and food safety. Graphene provides an excellent nanoplatform for SERS sensing due to its two-dimensional flat structure, uniform electronic and photonic properties, excellent mechanical stability, atomic uniformity, and high biocompatibility. In this review, we summarize recent advances in the fabrication of various graphene-based nanoplatforms for SERS sensing. We present the strategies, such as self-assembly, in situ synthesis, one-pot synthesis, liquid phase reduction, and biomimetic synthesis, for the fabrication of graphene-based hybrid metallic and alloy nanoplatforms, and then demonstrate the potential applications of graphene-based nanoplatforms for the SERS sensing of ions, organic dyes, pesticides, bacteria, DNA, proteins, cells, and other chemicals in great detail. In addition, we also discuss the future development of this interesting research field and provide several perspectives. This work will be helpful for readers to understand the fabrication and sensing mechanisms of graphene-based SERS sensing nanoplatforms; meanwhile, it will promote the development of new materials and novel methods for high performance sensing and biosensing applications.