Thermally stimulated current analysis in human blood.
In the recent years a lot of work has been published in the field of electrets effect in living and nonliving materials. It is the fundamental feature of these materials. This effect was studied in terms of thermo electrical, opto electrical, mechano electrical, photoelectrical and radio electrical properties generated due to change in structure in presence of light, heat, and mechanical stress on materials. The validity of TSC technique for blood analysis has already been reported by many researchers, where dielectric spectroscopy method was used to study the permeability and conductivity of blood and able to detect the difference between the malignant and normal blood cells [1-5]. The various parameters of blood are showing adequate changes in presence of heat and light.
The TSC spectra are affected by various factors such as glucose concentration, water content, protein concentration, blood group, concentration of red and white blood cells etc. In present case, the study of TSC is undertaken on known blood group and concentration of glucose. However, there is little existing literature on TSC behavior of healthy and diabetic patient blood sample. It is expected that this approach of blood diagnosis will give new information's about the health of human being. The aim of the experiment is to create the new approach for study of blood contents by means of thermally stimulated current.
In this experiment the samples of different blood groups were collected from healthy individuals of age group 20-25 years as well as diabetic patient and healthy person of age group 55-60 years. 10 [micro]l blood was taken on aluminum foil, which was well cleaned with ethyl alcohol before using. 80 [micro]m thick circular lining with another aluminum electrode covered the sample. The sample was immediately put into TSC device. The detail of TSC device is reported in literature . The time taken for preparation of sample was not more than 20sec. The blood did not coagulate during this period therefore no anticoagulants were used. The TSC is recorded by means of sensitive electrometer with the temperature at a rate of 3[degrees]C per minute. In another experiment the TSC is carried out on dried blood sample for which the blood is dried in air at room temperature for the period of 24h. The activation energy of TSC peak is calculated by initial rise method. Glucometer has been used to record the glucose level for each blood sample. The experiment was repeated for two times for each blood sample to analyse the experimental error, which was not more than [+ or -] 5%.
Results and Discussion
About 55% of blood is plasma, which contains many solute and remaining 45% blood is the mixture of red and white blood cells, platelets etc. In many laboratory analyses performed on blood serum, the fluid remaining after has completely clotted. We have considered the whole blood for TSC analysis.
The TSC behavior of healthy and diabetic blood is shown in figs.1-5. Figs.1-5 is characterized by two peaks. The observed current is found to be almost same for all sample of healthy blood, while peak position is different in different blood group. It is observed that diabetic blood samples show the remarkable higher value of current, which distinguishes it from the healthy blood. All samples have the higher value of glucose ranging from 180-250 mg/dl observed by glucometer. The observed activation energy value indicates that first peak for all samples of different blood group is mainly due to the denaturation of protein at low temperature. It seems that this peak is corresponds to glass transition temperature of red blood cells as reported in literature . Below glass transition temperature, the release of charge carriers from blood molecules is quite high in glucose contaminated blood sample rather than healthy blood sample. Both types of current (i.e. +ve and -ve) have been recorded in present case. The blood compounds such as cholesterol derivatives, some proteins phospolipid etc might have liquid crystalline properties [8-9]. The charge generation and dipole orientation occurs due to contact electrification. When two different materials contact and separate, an electrical charge transfer from one surface to the other can take place because of the different electronic structures of the two materials. In the present case charges are mainly generated due to the difference in work function of liquid dielectric and Teflon lining, causes the contact electrification. The appearance of first TSC peak at low temperature is mainly due to following reasons:
The transfer rate of charge carriers from metal into blood is initially quite high, but at certain temperature it decreases exponentially and giving rise to the low temperature peak.
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
The polar group in blood compound is hydrophilic in nature; therefore hydrate cells are formed around it. The hydrogen bonds in these cells extend the polar fragments in organic compound causes the polarization in blood. The mean energy of hydrogen bond is 0.1-0.25eV , while the activation energy of first TSC peak is 0.41 eV. This indicates the large number of hydrogen bond broken under this TSC peak. The complex structures of blood containing the polar groups, which are suppose to be oriented in presence of heat. The bonding energy of hydrogen molecule is quite less than activation energy. It seems that thermal decomposition of protein occurred at low temperature range might be the reason of TSC peak. The stability of protein is subjected to survival of hydrogen bond, since hydrogen bond cannot survive at higher value of energy, which is corresponds to calculated value of activation energy.
The dielectric constant is one of the basic parameter, which plays an important role in the determination of material properties. It depends upon dipole moment, polarizibility, molecular radius, dielectric susceptibility etc. The dipolar behavior of blood is very much clear by dependence of refractive index on temperature. The dielectric constant is the function of refractive index as from Maxwell's equation
[epsilon] = [n.sup.2] .......(1)
Differentiating above equation with respect to temperature T
d[epsilon]/dT = 2ndn/dT .......(2)
Above relation clearly shows that dielectric constant of liquid blood is very much effected by temperature .
Hydration of protein  is one of their important properties. At room temperature, the fraction of bound water to hemoglobin is quite less. The water bound to hemoglobin is osmotically inactive as compared with the free osmotically active one. We postulate that when the temperature is raised above the critical temperature, the concentrated blood undergoes a high-to-low viscosity transformation mediated by a partial loss of water resulted the decrease in viscosity. In a simple approach, we considered a compact arrangement of molecules and their thermal behavior is corresponding to the TSC as observed in our experiment. The temperature for which the hydration of protein is started is the critical temperature. In all cases low temperature peak is well corresponds to it.
The high temperature blood protein losses its native conformation and these changes are irreversible. As the temperature is increased, a number of bonds in the protein molecule are weakened. As these bonds are first weakened and broken, the protein obtains a more flexible structure and the groups are exposed to solvent. As heating continues, some of the cooperative hydrogen bonds that stabilize helical structure will begin to break. As these bonds are broken, water can interact with and form new hydrogen bonds with the amide nitrogen and carbonyl oxygen of the peptide bonds. The presence of water further weakens nearby hydrogen bonds causes an increase in the effective dielectric constant near to it. As the helical structure is broken, hydrophobic groups are exposed to the blood water. The energy required for denaturation of protein is approximately equal to free energy (?E). This free energy is released from natural state to the denatured state. The following relation gives the free energy 
[DELTA]E = [E.sub.n] - [E.sub.d] ......(3)
The energy liberated due to the interaction between polar and nonpolar molecules of protein with blood water at a certain temperature might be the origin of dipolar polarization. The calculated value of activation energy is an evidence of dipolar polarization.
The high temperature peak ranges from 100-115[degrees]C in all cases, it may be due to the phase transition takes place by changing the liquid state of blood into dry state. The destruction of organic compounds is occurred due to the denaturation of protein, conglomeration of lipid shell etc. at high temperature.
The reason of positive TSC peak is the exposure of most proteins to high temperature results in irreversible denaturation [11,13]. Some proteins, like caseins, however, contain little if any secondary structure and have managed to remove their hydrophobic groups from contact with the blood water without the need for extensive structure. The lack of secondary structure causes these proteins to be extremely resistant to thermal denaturation, which causes the thermal decay of real charges. In this state Maxwell Wagner effect  seems to be true because it offers the decay of real charges as observed in present case. The positive TSC peak in blood is reported in literature  and could be interpreted in different way.
In presence of functional polar group in blood and other can ionize. For example, if the hydrogen ion is removed from the -COOH group, the oxygen will retain both of the electrons it shared with the hydrogen and will have a negative charge. The hydrogen that is removed leaves behind its electron and is now a hydrogen ion (proton). The total current flowing in output circuit is the sum of current carrying by electron and current carrying by proton. If the current is due to the proton then polarity of TSC will be negative, while it is flowing through the electron the polarity of current is positive and TSC is governed by this mechanism. The TSC for dried sample in absence of Teflon lining characterized by two narrow peaks. It is very clear from the fig 1-5 the high temperature peak is shifted from higher to lower temperature from blood group O+ to A+ which leads the blood group diagnosis on the basis of TSC peak position.
The appearance of positive peaks in diabetic blood distinguishes it from normal blood. The position of peak and polarity of TSC is highly effected by concentration of glucose. It has been observed that the negative peak is disappeared in the blood of high glucose concentration. The TSC of normal blood (A+ blood group) of 55-60-year-old healthy persons is shown in fig. 6. TSC shows similar behaviour as shown by TSC of young healthy person of age group 20-25 year old. TSC shows the weak current as compare to young healthy person because of destruction of blood organism in old age. We can distinguish the TSC of normal blood of age group 55-60 and diabetic blood in following way:
1. TSC of diabetic blood shows almost positive current as compare to normal blood.
2. The magnitude of TSC for diabetic blood is much greater than TSC of normal blood.
It seems that glucose concentration favours the positive TSC. Therefore, TSC of pure glucose have been recorded. The buffer solution of pH 7.5 has been used to dissolve the pure glucose for TSC study since this is close to the physiological pH of blood. The positive polarity of TSC in pure glucose (fig.7) sample is an evidence of more positive current region observed in diabetic blood. The magnitude of pure glucose TSC is comparatively higher than the diabetic blood TSC, because no other contents are present in pure glucose samples. The change in polarity of the high temperature peak in blood sample may be due to glucose concentration and certain vital cycles of the human organism such as reversible biochemical cycles in blood, which are followed by formation of positive and negative potentials in the double electric layer surrounding the blood cells . The polarity of TSC is also affected due to the physiological factors such as blood pressure, presence of stimulator etc. However, the explanations about the change in polarity of TSC peak are speculative at present but the subject requires detail study and explanation.
[FIGURE 6 OMITTED]
[FIGURE 7 OMITTED]
The TSC study is informative for various parameters concerning to blood. Present study reveals the very important result for identification of blood group and concentration of glucose in blood, which is based on TSC peak position. The appearance of high positive current in pure glucose is an agreement with TSC of diabetic blood. It is concluded that TSC may be very effective tool to develop the new generation of biosensor for diagnosis of blood contents.
We (M. S. Gaur and Prashant Shukla) gratefully acknowledge the financial support of the Uttar Pradesh Council of Science and Technology, Lucknow (U.P.) India. The support of Dr. S. K. Kasyap, Medical Officer, Hindustan College of Science and Technology, is highly acknowledged.
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M. S. Gaur * (1), R. K. Tiwari (1), Prashant Shukla (1), Pooja Saxena (1), Karuna Gaur (2) and Udita Tiwari (3)
(1.) Department of Physics, Hindustan College of Science and Technology, Farah, Mathura (U.P.)
(2.) Department of Bioscience, R.D.Govt. Girls College, Bharatpur (Raj.)
(3.) Department of Biochemistry, Institute of Life Sciences, Dr.B.R.A.University, Agra (U.P.)
* Corresponding Author Email: firstname.lastname@example.org, Fax: +91 565 2763364
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|Author:||Gaur, M.S.; Tiwari, R.K.; Shukla, Prashant; Saxena, Pooja; Gaur, Karuna; Tiwari, Udita|
|Publication:||Trends in Biomaterials and Artificial Organs|
|Date:||Jul 1, 2007|
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