Raman spectroscopy is an increasingly popular technique in many areas including biology and medicine. It is based on Raman scattering, a phenomenon in which incident photons lose or gain energy via interactions with vibrating molecules in a sample. These energy shifts can be used to obtain information regarding molecular composition of the sample with very high accuracy. Applications of Raman spectroscopy in the life sciences have included quantification of biomolecules, hyperspectral molecular imaging of cells and tissue, medical diagnosis, and others.

Surface-enhanced Raman scattering (SERS) spectroscopy is currently a well-established analytical technique, as it offers many advantages over other spectroscopic or spectrometric techniques such as Fourier transform infrared (IR) spectroscopy, near-infrared (NIR) absorption, UV-vis absorption, fluorescence, nuclear magnetic resonance (NMR), X-ray diffraction, X-ray photoelectron spectroscopy or mass spectrometry. The implementation of Raman scattering-based techniques for life science applications is becoming very popular as they can extract a significant amount of information directly (with no need for prior sample preparation) from complex environments such as biological fluids, living tissues and cells (including sensitivity for small structural changes in macromolecules, non-invasive sampling capability, minimum sample preparation and high spatial resolution). Besides, the most significant drawback of normal Raman scattering (RS) spectroscopy for analytical applications, i.e. the inherently weak cross-section, is overcome in SERS by exciting the sample in contact with a ‘plasmonic’ surface with an appropriate laser line. Under such conditions, the Raman cross-section and, in turn, the signal intensity are extraordinarily increased so that levels of detection down to the single-molecule can be reached while retaining all the structural information provided by RS. Thus, it is clear that the advancement in SERS detection is linked to the progress in the synthesis and optical characterization of new nanostructured materials.

SERS has been established as a solid and reliable analytical technique for the detection of extremely low amounts of a wide variety of molecular species. Although the requirement of close contact of the analyte with the enhancing metallic surface has been a limitation, the design of novel hybrid substrates opened up the possibility of complete generalization of SERS detection. Additionally, through the use of antibodies or other selective receptors that can be bound to the nanostructured metal surface, recognition can be made specific and even quantitative. This is extremely important for biomedical applications since it is the basis of early diagnosis of important diseases.

Rapid Diagnostic Test Applications:
1. Genetic diagnostics, immunoassay labelling and trace amount detection of drugs, biomolecules and pesticides. (The tremendous progress that has been achieved in both colloid chemistry and lithographic methods resulted in the possibility of tuning the optical properties within the whole range from the UV to the NIR, through careful control over the morphology of the nanoparticles)
2. Single algal cell detection.
3. Clinical biomarkers: Protein, DNAs, hormones, viruses, bacteria, and toxins.
4. SERS combined with plasmonic sensing can be used for high-sensitivity and quantitative detection of biomolecular interaction, and to study redox processes at the single-molecule level.