Progress in vibrational spectroscopy in diagnosis and screening

Abstract

Vibrational spectroscopy has a great potential in diagnosis and screening with increasing number of applications in biological and biomedical fields, food and environmental sciences and forensic area. This review focuses on the historical background and recent developments related to the use of this technique in various areas of diagnosis and screening. Vibrational spectroscopy consists of some of the oldest methods that are used in the analysis of sam- ples. William Herschel discovered the infrared region of electromagnetic radiation in 1800 (2). Before that, the strength of infrared spectroscopy for structural characterization of molecules was known and it was admitted as a significant method to analyse the structure of biological molecules in addition to X-ray diffraction. and terahertz (THz) spectroscopy are the other currently used vibrational spectroscopic tech- niques to understand structure and composition of biological samples. The basic theory of the Raman effect was developed by Chandrasekhara Venkata in 1928 (29), while THz spectroscopy was discovered in 1988 (33). All of these techniques based on the transitions between vibrational energy levels of molecules as a result of absorbtion of electromagnetic radiation. The region between 14,000 and 4c m −1 of the electromagnetic radiation is called as infrared region which is divided into three sub- regions as near-infrared region (14,000 to 4,000 cm −1 ), mid-infrared region (4,000 to 400 cm −1 )a nd far-infrared region (400 cm −1 to 4c m −1 ). However, the THz spectral region from 10 THz (333 cm −1 ) − 1t o 0.06 THz (2 cm −1 ) has generally been used in biophysics and biochemistry. In spec- troscopy, transition between vibrational energy levels is induced by ultraviolet (UV), visible (VIS) or NIR. According to the quantum theory, this is a low probability event, because incident radiation does not match the energy differences between vibrational energy states that are used in spectroscopy. In spectroscopy, a small amount of energy of an incident photon can be transfered to one of the molecules that causes transition of molecule to the higher vibrational state. The energy lost of the incident photon is equal to the energy of a transition from one vibrational state to another. Since a