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ABSORPTION AND DIFFUSION MEASUREMENT OF BIOLOGICAL SAMPLES USING A FREE ELECTRON LASER. M. D’Arienzo,A. Doria, G.P. Gallerano, E. Giovenale, A. Lai, G. Messina, D. Piccinelli ENEA C.R.Frascati, Via Enrico Fermi 45, 00044 Frascati (Italy). Why Terahertz?.
M. D’Arienzo,A. Doria, G.P. Gallerano, E. Giovenale, A. Lai, G. Messina, D. Piccinelli
ENEA C.R.Frascati, Via Enrico Fermi 45, 00044 Frascati (Italy)
Terahertz radiation corresponds to:
FREQUENCY (0.1 - 20) THz
WAVELENGTH (3000 - 15) mm
WAVENUMBER (3 - 700) cm-1
ENERGY ( 0.4 - 80 ) meV
Within the THz-BRIDGE project the ENEA team carried out different experimental
activities among which the irradiation of:
Some theoretical calculations have been carried out to modelize the interaction of
THz radiation with scattering elements within the various samples. In particular
scattering of 120 GHz radiation with lymphocytes and lyposomes has been studied.
The THz beam coming from the light pipe into the TDS is first focused down to a 17.5 mm diameter aperture by means of a conical section and is then let expand by diffraction to about 52 mm diameter to match the required irradiation area.
Transmission through polystyrene dishes
and optical properties of polystyrene in the THz region.
nominal thickness (cm)Experimental results
Water absorption of THz radiation
Such values are close to the absorption coefficient of water at room temperature. The value of the absorption
coefficient measured for whole blood shows that less than 1% of the incident radiation penetrates through
1 mm thickness. Although weak scattering by blood cells does not cause a significant displacement from
the exponential attenuation law, it is responsible of the difference in transmission between whole blood
and physiologic solution.
The interaction of cellular systems with their environment occurs primarily through the cell membrane. Studies on different kind of cells indicate that millimeter-wave radiation may alter membrane structural and functional properties that control cellular response. One of the membrane functions is the transport of substances into and out of cell. This transport through the membrane can involve the lipid bilayer as well as the membrane proteins.
A very simple membrane model, such as that provided by liposomes, will be used to study the permeability of a simple bilayer in response to THz radiation in absence of interfering reactions. This model consists of lipid vesicles enclosing in their interior a soluble enzyme, such as the carbonic anhydrase (CA).
“Liposomesfilled with carbonic
A liposome membrane
containing a water filled
Mean size of a liposome: 50 nm
----------- “Empty” Lyposome
----------- Trisaline solution with enzie
----------- Trisaline solution
1200Experimental results on liposomes and tris-saline solution
Systematic offset owed
to “meniscus effect”
at the edge of the Petri
Experimental absorbing coefficients
EMPTY LIPOSOMES: (503) cm-1
FILLED LIPOSOMES: (553) cm-1
TRIS-SALINE SOLUTION: (438) cm-1
TRIS-SALINE SOL. With ENZYME: (488) cm-1
An external shell (lipid membrane whose refractive index is the same of fat at 120 GHz 1.6-0.5i)
An inner core four times bigger (the water or ahnydrase vesicle whose refractive index can be approximated to water at 120 GHz 3.4-1.9i)Theoretical approach: Mie simulations I
Mie calculations show the reduced cross sections defined as:
versus Mie parameter defined as:
Mie parameter in this case is ~ 0.001
The extinction is owed to absorption of radiation up to a value of the Mie parameter ~ 0.8
Reduced cross section of the external membrane: in the range 0-1 for the Mie parameter, extinction of radiation is again owed to absorption rather than scattering
1Theoretical approach: Mie simulations II
What kind of information do we expect to find out from the experiment?
..which are the optical properties of lymphocytes.
..if there is any resonant absorption at 120 GHz
..which are the scattering properties of lymphocytes
(diffusive regime or ballistic?)
Approximately we can calculate the Rayleigh scattering and absorbing cross sections of lhympocytes in 2-propanol and in blood, considering for the latter one the same optical properties of water (which is basically made of) :
Thus scattering is almost absent in the process. All the electromagnetic energy is absorbed by the particle. The absorbing properties are described by the complex dielectric constant of the particle
Thus, there is a need to find a THz transparent liquid solution as surrounding medium.
Alcoholic solutions showed weakly absorbing properties in the THz range of frequency.
2-Propanol (or Isopropylic alcohol) presented the lowest absorption coefficient
The survival time of lymphocytes in 2-propanol has been measured and it
resulted in about 10 minutes.
1200Experimental results on 2-propanol and lymphocytes I
= (4.5±0.5) cm-1
2-Propanol + lymphocytes
= (5±0.5) cm-1
Density of lymphocytes in 2-propanol:
Within the experimental error it’ s impossible to distinguish the two curves (and thus the two absorption coefficients)
Since the absorption coefficient is related to the absorption cross section by the equation:
We can use the upper limit of a (0.5 cm-1) to estimate the experimental absorption cross section of the process:
We can also calculate the geometric cross section (being the medium radius of a lymphocyte 5 m):
3Theoretical approach: Mie simulations
Thus, a guessed reasonable (yet not true) value of the refractive index has been considered for lymphocytes.
Lymphocytes refractive index: 1.5-0.5i
Mie parameter ~ 0.04