text: While SERS can be performed in colloidal solutions, today the most common method for performing SERS measurements is by depositing a liquid sample onto a silicon or glass surface with a nanostructured noble metal surface. While the first experiments were performed on electrochemically roughened silver, now surfaces are often prepared using a distribution of metal nanoparticles on the surface as well as using lithography or porous silicon as a support. Two dimensional silicon nanopillars decorated with silver have also been used to create SERS active substrates. The most common metals used for plasmonic surfaces in visible light SERS are silver and gold; however, aluminium has recently been explored as an alternative plasmonic material, because its plasmon band is in the UV region, contrary to silver and gold. Hence, there is great interest in using aluminium for UV SERS. It has, however, surprisingly also been shown to have a large enhancement in the infrared, which is not fully understood. In the current decade, it has been recognized that the cost of SERS substrates must be reduced in order to become a commonly used analytical chemistry measurement technique. To meet this need, plasmonic paper has experienced widespread attention in the field, with highly sensitive SERS substrates being formed through approaches such as soaking, in-situ synthesis, screen printing and inkjet printing.
  The shape and size of the metal nanoparticles strongly affect the strength of the enhancement because these factors influence the ratio of absorption and scattering events. There is an ideal size for these particles, and an ideal surface thickness for each experiment. If concentration and particle size can be tuned better for each experiment this will go a long way in the cost reduction of substrates. Particles that are too large allow the excitation of multipoles, which are nonradiative. As only the dipole transition leads to Raman scattering, the higher-order transitions will cause a decrease in the overall efficiency of the enhancement. Particles that are too small lose their electrical conductance and cannot enhance the field. When the particle size approaches a few atoms, the definition of a plasmon does not hold, as there must be a large collection of electrons to oscillate together.
  An ideal SERS substrate must possess high uniformity and high field enhancement. Such substrates can be fabricated on a wafer scale and label-free superresolution microscopy has also been demonstrated using the fluctuations of surface enhanced Raman scattering signal on such highly uniform, high-performance plasmonic metasurfaces.
  Due to their unique physical and chemical properties, two-dimensional (2D) materials have gained significant attention as alternative substrates for surface-enhanced Raman spectroscopy (SERS). The use of 2D materials as SERS substrates offers several advantages over traditional metal substrates, including high sensitivity, reproducibility, and chemical stability.
  Graphene is one of the most widely studied 2D materials for SERS applications. Graphene has a high surface area, high electron mobility, and excellent chemical stability, making it an attractive substrate for SERS. Graphene-based SERS sensors have also been shown to be highly reproducible and stable, making them attractive for real-world applications. In addition to graphene, other 2D materials, especially MXenes, have also been investigated for SERS applications. MXenes have a high surface area, good electrical conductivity, and chemical stability, making them attractive for SERS applications. As a result, MXene-based SERS sensors have been used to detect various analytes, including organic molecules,  drugs and their metabolites.
  As research and development continue, 2D materials-based SERS sensors will likely be more widely used in various industries, including environmental monitoring, healthcare, and food safety.