Terahertz Spectroscopy in Bio systems and Biomedical Applications
Amit Kumar Bhunia*1,2
1Department of physics and Technophysics, Vidyasagar University, India
2Department of Physics, Government General Degree College at Gopiballavpur-II, India
Submission: August 30, 2017; Published: October 26, 2017
*Corresponding author: Amit Kumar Bhunia, Department of Physics & Technophysics, Vidyasagar University, Paschim Medinipur & Department of Physics, Government General Degree College at Gopiballavpur-II, Beliaberh, Paschim Medinipur-721517, India, Email: email@example.com
How to cite this article: Amit K B. Terahertz Spectroscopy in Bio systems and Biomedical Applications. Curr Trends Biomedical Eng & Biosci. 2017; 10(1):
555780. DOI: 10.19080/CTBEB.2017.10.555780.
The terahertz radiation has very low photon energy and it does not create any ionization hazard for biological systems. It is strongly attenuated by water and very sensitive to water content. Unique absorption spectra due to intermolecular vibrations in this region have been found in different biological materials. Terahertz (THz) spectroscopy provides a powerful tool for characterization of a great many bio molecules and tissues. The unique features of THz make terahertz imaging very attractive for medical applications over the existing imaging techniques. The interest in terahertz imaging and spectroscopy of biologically related applications increasing more and more within the last few years. This paper provides a short review of terahertz spectroscopy in bio systems and recent advances in terahertz spectroscopy techniques in biomedical applications.
Terahertz (THz) radiation (also called T-Rays) is electromagnetic waves between microwaves and the infrared optical band. Its frequency range lies within the range of 0.1 to 20THz . 1THz is equivalent to 33.3cm-1 (wave numbers), or 0.004eV photon energy, or 300μm wavelength.
Terahertz spectroscopy is a powerful tool for characterizing vibrational modes  and can probe physical phenomena such as low-energy excitations and carrier dynamics in electronic materials, collective vibrational or torsional modes in condensed-phase media, and rotational and vibrational transitions in molecules [2,3]. Terahertz spectroscopy can directly assess the electric field amplitude (Figure 1). Therefore, the amplitude and phase of the post-sample analyzed signal can be obtained directly and simultaneously using a Fourier transforms [4,5]. As a result, terahertz radiation now has widespread potential applications in communications, materials, chemistry, Biosensors, Terahertz Imaging, Tissue Spectroscopy, pharmaceutical, and many other fields (Figure 2). The technology on THz time domain spectroscopy based on laser sources has been promoted as one of the disruptive technologies changing the world [6,7]. THz radiation can penetrate up to several millimetres inside the thin layers of non-metallic substances like plastic, ceramics, and clothing.
Now a day’s X-ray is important tools in radiographic imaging technology. Due to ionizing properties of X-ray radiation, it causes some bad effects to our health [8-10]. On the other hand, Terahertz waves are non-ionizing and therefore they do not pose a risk to living organisms. They provide images that are comparable to backscatter X-rays. Although THz has lower resolution than X-Ray, but in many fields of application, it is a more preferable technique . Terahertz technology also produces faster results than X-ray and enables non destructive,
internal, chemical analysis of materials with applications in a
number of industries. The advanced drug delivery techniques
with sophisticated surface coatings, any matrix structures,
require complex processes for the production of such structures
to ensure the quality of the resulting product.
The most common and convenient form of administering
drug to a patient is tablet. The most important factors during
the manufacturing process are the microstructure, distribution,
particle size and morphology of the drug molecules. These
factors should properly maintain in a tablet. As THz spectroscopy
give rise non-destructive imaging technology, pharmaceutical
industry uses it to assess the microstructure of the tablet
throughout product development and manufacturing in order
to ensure its quality while optimizing the productivity. The THz
spectroscope can ensure the quality by inspecting chemical
as well as morphological composition. As compared to other
competitive methods like Infrared, FTIR, Raman and X-ray
tomography, the THz technology is capable of mapping and
analyzing the internal structures within complex pharmaceutical
products non destructively to reveal structural defects. THz
technology can be used for semiconductor inspection, food
inspection, pharmaceutical inspection, and 2D and 3D imaging,
including medical diagnosis in the areas of skin cancer, THz-3DCT
images, tooth structure and tumours [9-11].
THz reflection pulse imaging was used to study human
skin in vivo. Pickwell  used broadband THz pulsed imaging
system of frequencies approximately 0.5-2.5THz for investigated
freshly excised human tissues. THz imaging was used for oral
cancer diagnosis . Wittlin  studied the temperature
(from 5-300K) dependent properties of highly oriented films
of DNA salts, Li-DNA and Na-DNA in the THz region (0.090-
13.5THz). They identified five vibrational modes including the
lowest frequency modes at 1.35THz for Li-DNA and 1.23THz
for Na-DNA. They suggested that a simple lattice dynamical
model was reasonably successful in explaining the presence of
vibrational modes and the impact of hydration on these modes.
The Markelz group  investigate THz response of several
proteins using THz-TDS including hen egg white lysozyme, horse
heart myoglobin and bacteriorhodopsin. For Lysozyme and
myoglobin powder, broadband absorption without identifiable
peaks was observed to increase from 5-40cm-1 and then leveled
off near 80cm-1.
Upadhya  demonstrated the use of terahertz timedomain
spectroscopy for measuring absorption spectra in Dand
L-glucose, sucrose, uric acid and Allenton. They suggest that
the intermolecular vibrational modes may contribute in the THz
frequency range in the molecular spectra of these molecules.
Fitzgeret  studied the information about the optical
properties of human tissue, using a broadband terahertz pulsed
imaging system comprising frequencies approximately 0.5 to
2.5THz. They calculate the refractive index and linear absorption
coefficient of skin, Adipose tissues, Striated muscle, Vein, Nerve.
They observed the higher value of refractive index for De-ionised
water (2.04±0.07) than any tissue in the THz region. The linear
absorption coefficient of muscle is higher than adipose tissue.
The higher value of linear absorption for muscle is expected from
the higher hydration of muscle. As these samples came from that
in vivo clinical a single subject, there is currently insufficient
statistical power to draw firm conclusions, but results suggest
imaging will be feasible in certain applications [18-21].
The performance of any THz imager depends on two factors:
A. The THz source power and the corresponding detector
responsively and sensitivity,
B. The system losses, including component and material
absorptions, dispersion and scattering.
Therefore, the suitability of a particular imaging technique
to be employed towards a specific application is dependent
on the optimized design of the imaging arrangement based on
the abovementioned parameters. The difference frequency
generation (DFG) is an important technique for THz generation.
This technique is suitable for deployment in a 2D THz imaging
system because it has the potential for narrow line width and
wide tuning range (Figure 3).
THz imaging has the potential to be used in assessing
several structures. The development of techniques which utilize
terahertz waves for applications in medicine is growing rapidly
with the development of instrumentation. Future studies will
focus on increasing the resolution of the sampled area and
imaging human structures upon reflection in 3-D.
Bakopoulos et al.  demonstrate recent advances
toward the development of a novel 2D THz imaging system
for brain imaging applications both at the macroscopic and
at the bimolecular level. Ouchi  developed a high efficient
terahertz sources and detectors for THz imaging and other
medical applications. They used a ridge waveguide with 5-7μm
width and LiNbO3 based nonlinear terahertz generator. They
demonstrated three dimensional imaging of biological tissues.
Their observation included differences in physical properties
between tumor tissues and normal tissues
Ji  designed and fabricated a novel terahertz (THz)
otoscope. They suggest that their otoscope can help physicians
to diagnose otitis media (OM) with both THz diagnostics and
conventional optical diagnostics. Recentlty THz bio-sensing
micro chip for detecting illicit drugs has been developed.
Hernandez-Cardoso  proposes that terahertz reflection
imaging method is an important tool for the detection of diabetic
foot syndrome in its early stages.