Surface-enhanced Raman spectroscopy (SERS) utilizes specialized metal substrates to allow Raman signal enhancement up to 10 orders of magnitude. This phenomenon occurs when the molecules of interest are in very close proximity to the metal substrate, and is generally used for evaporated solutions or particle-surface characterization. The enhanced Raman signal with SERS has extended its applications in many fields, such as biological studies, to quantify trace substances or identify very small structures such as cell surface proteins. Intracellular SERS is also possible, via the injection of metallic nanoparticles, to study internal structures and analytes.