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Raman Spectroscopy
RS is the measurement of molecular vibrations in form of the inelastically scattered light from a molecule. Unlike the Infrared, Raman spectroscopy can be employed with wide range of wavelength that extends from UV to Near-IR. However, Raman and IR spectroscopy provide complementary information. Today, Raman spectroscopy (RS) is applied in most of the organic as well as inorganic studies.

Raman Application
One of the largest applications of RS in the biomedical field is proteomics, where the function, kinetics and structure of the protein can be estimated. RS applications are also established in medicine and cover studies:

• on tissues, including brain tissues
• kidney stones
• the distribution of cystiene crystals in the liver
• single cell and group of cells including cancer cells
• teeth
• DNA and drugs and their binding to receptors cellular
• diagnostics studies such as breast cancer

RS has also been used in art history and conservation, especially for pigment and binding materials identifications. Generally, it is used for structural determination, multicomponent qualitative and quantitative analyses.

In general, RS can be employed for:

• Smaller molecules: nuclear acids, peptides, purine and pyrimidine
• Larger molecules: protein, DNA and RNA
• Intrinsically coloured molecules such as chlorophylls, other pigments and proteins containing haem
• Detection of simulating drugs
• Interaction of anti-tumor drugs with DNA
• Monitor transportation through membranes
• Charge transfer processes
• Detection of micro-organisms
• Immuno-assays
• DNA and gene probes

Multifold Raman
RS became more powerful when the Surface Enhanced effect was discovered and applied together with RS to compose what is today known as SERS. This technique enables detection of a Raman signal that is up to 14 orders of magnitude stronger than a Raman signal. Today, there are different Raman techniques applied in almost all the fields of research, diagnostics and analysis. Most of these techniques can be adapted within our BioRaman, e.g.:

• FT-Raman Spectroscopy
• ROA
• SERS and SERRS

Raman Theory
The Raman scattering transition moment is:

R = < X_i | α | X_f >

where X_i and X_f are the initial and final states, respectively, and α is the polarizability of the molecule:

α = α₀ + (r-r_i)(dα/dr) + ... higher terms

where r is the distance between atoms and α₀ is the polarizability at the equilibrium bond length, r_e. Polarizability can be defined as the ease of which an electron cloud can be distorted by an external electric field.

Since a₀ is a constant and < X_i | X_j > = 0, R simplifies to:

R = < X_i | (r-r_e) (dα/dr) | X_j >

The result is that there must be a change in polarizability during the vibration for that vibration to inelastically scatter radiation.
The polarizability depends on how tightly the electrons are bound to the nuclei, and it is a function of the vibrational coordinates Q. In the symmetric stretch the strength of electron binding is different between the minimum and maximum internuclear distances. Therefore the polarizability changes during the vibration and this vibrational mode scatters Raman light (the vibration is Raman active). In the asymmetric stretch the electrons are more easily polarized in the bond that expands but are less easily polarized in the bond that compresses. There is no overall change in polarizability and the asymmetric stretch is Raman inactive. Raman line intensities are proportional to:

ν⁴ * σ(ν) * I * exp(-Ei/kT) * C

where ν is the frequency of the incident radiation, σ(ν) is the Raman cross section (typically 10-29 cm2), I is the radiation intensity, exp(-Ei/kT) is the Boltzmann factor for state i, and C is the concentration.