Opto-electronic system with optical fibres sensor for ionic concentration measurement into sanguine serum.

Chita, Monica Anca ; Sima, Ion ; Stirbu, Cosmin 等

1. INTRODUCTION

The experimental part of this paper it refers at realisation of a chemical sensor, which uses the fluorescence phenomena of fluorescein.

The most used chemical indicators in the optical fibres technique (Stanciu & Stanciu, 2003) are they that use absorption and fluorescence phenomena, the last variant being preferred because it presents a higher sensitivity. One of the important class of fluorescence chemical indicators (Eggins, 2002) is the of ftaleines, the most important and used ftaleinels being the fluorescein: [C.sub.20][H.sub.12][O.sub.5] (the neutral form).

So the fluorescein (Wolfbeis, 1991) and his derivates are the very used indicators in the case of the chemical optrods wits optical fibres. The fluorescein may be founds in the neutral form; for low pH values, fluorescein appears under the colourless lactones form. Through molecular rearrangement it obtains the chinoid neutral form.

In the experiment it was used the sodium salt of fluorescein ([C.sub.20][H.sub.12][O.sub.5][Na.sub.2]). It presents like a brick dust colour and in order to be used as indicator it is necessary to admix it with distillate water. The tampon solution obtained is yellow-green coloured and it can be used for the ionic analysis of sanguine serum.

2. THE BLOCK SCHEME OF THE EXPERIMENTAL OPTO-ELECTRONIC SYSTEM

The opto-electronic system used for the experimental determinations has the experimental scheme presented in the fig. 1 and contains:

* the optrod interfaces with two optical fibres PMMA;

* a light source, namely a blue "ultrabright" LED;

* an ORIEL-7180 photodiode;

* an optical filter;

* a multifunctional electro-optical source for the LED command;

* a received electronic block.

[FIGURE 1 OMITTED]

Lowing from the spectral characteristics of fluorescein it was decided its use as fluorescent indicator (Stanciu et al., 1997) for concentration measurement of some ionics species presented generally into chemical solutions and particularly into sanguine serum.

3. EXPERIMENTAL DATA

In the sanguine serum case the following steps were followed:

* it was selected three serum samples (in three days);

* it was choosed twenty one valid probes;

* for the valid probes it was made the partial ionograme, respectively, it was determined the concentration of total calcium, of magnesium, sodium and potassium ions;

* for the valid probes it was measured pH with using a digital pH-meter CORNING-150 having electrode with lateral membrane and internal temperature compensation;

* after the presented determination, the serum probes was marked with fluorescein (fluorescein was initial dissolved in distillate water, fluorescein concentration being [10.sup.-3]; this "marked" substance was mixed in 1% proportion with sanguine serum, corresponding of different values of pH);

* the measures made with the electro-optical system with optical fibres were unfurled at the room temperature (23[degrees]C).

As about the normal values domain of the physiological pH, in literature is specified that it is light basic, the usual domain being, 7 / 7.4 and normal average value being 7.2 (Lown & Prichard, 2003). For the sanguine serum from the effected measures, it was ascertained that this domain is 8.3 / 8.8. The explanation of this phenomenon consists in the fact that the measures were effected in-vitro (after the blood harvesting): in contact with the air, the concentration of hydrogen ions decreases because a part of them tie of the oxygen ions from air, forming the hydroxilical groups (O[H.sup.-]). From the definition relation of pH results that pH value increases. The equilibrium corresponding of a new state is extremely rapid reached. This was put in evidence through three measurements of pH (with indicator paper and with digital pH-meter CORNING--150), five minutes after the harvesting of three blood samples. The following specification must be made: the measurements cannot be effected on the integral blood, because the existing "residues" (including the red cells) load the pH electrode membrane. The serum is obtained through the natural decantation at room temperature and the process build about one hour. The only solution was to work on plasma which can be obtained in few minutes through centrifugation. The measurements pointed out that pH value was the same for the serum and plasma.

Also it was ascertained that after three days (3x24 hours) the value of pH was modified slight enough (under 0.1 pH units), in the conditions in which in this period the probes was freeze. This thing do not happens however for the other ions, the prescriptions emphasized that the measurements must be made the same day in which it harvests the blood.

As about the voltage variation [U.sub.0vv-f] as a function of pH, it ascertains an enough large dispersion of the values (fig. 2). The causes of this phenomenon are:

* the used optrod do not have a selective-permeable membrane and sanguine serum is a mixture of organic compounds, including proteins, which interactions with the fluorescein affecting its selectivity for hydrogen ions;

* the displacement of the pH values for the sanguine serum in-vitro in the range 8.3 / 8.8, zone of reduced sensitivity of fluorescein (the maximum sensibility of the fluorescent marker is at pH = pKa, respectively at 6.4 / 6.5 in this case);

* the measurements could not be effected at the human body temperature (the sanguine analysers, function of the measured measure, achieves the measures after bringing probes to 37[degrees]C temperature).

[FIGURE 2 OMITTED]

For the values obtained by measure, the regression straight line, [U.sub.0vv-r] = f(pH), was calculated and represented in the fig. 2 too.

Also it was represented the dependence between the useful voltage [U.sub.0vv-f] and the concentration of the calcium, magnesium, sodium and potassium ions (fig. 3, fig. 4 and fig. 5).

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

4. CONCLUSIONS

The performed study described the behaviour of a fluorescence marker (fluorescein) into sanguine serum, in the presence of hydrogen, calcium, magnesium and sodium ions. Also, the presented system can be used for subsequent studies concerning the behaviour of other fluorescence markers, as into tampon chemical solutions, or into complex organic solutions, such as sanguine serum. These studies can emphasise the marker selectivity under different conditions.

Another important advantage of the measurement system is that it is very flexible, allowing very diverse studies in this field, including the adaptation for sensors with selective-permeable membranes.

Obviously, the study will be continued in order to observe the influence of red blood cells (the main suspect of the values dispersion), and others measurements too.

5. REFERENCES

Eggins, B. (2002). Chemical Sensors and Biosensors, Wiley & Sons, Inc., ISBN 9780471899143, New York, USA.

Lawn, L. & Prichard, E. (2003). Measurement of pH, Royal Society of Chemistry Edition, ISBN13: 9780854044733, Cambridge, UK.

Stanciu, M & Stanciu, A.D. (2003). Chemical and biochemical sensors with optical fibres, Electra Edition, ISBN 9738067-92-8, Bucharest, Romania.

Stanciu, M.; Iliescu, C.; Pantelimon, B. & Ilie, L (1997). The use of optical fibres sensors with fluorescence indicator for the pH measure. The First international Conference of Electromechanical Systems, pp.265-268, ISBN 9975-910-22-X, Chisinau, October 1997, University of Chisinau, Chisinau, Republica Moldova.

Wolfbeis, O. (1991). Fiber Optic Chemical Sensors and Biosensors, Boca Raton: CRC Press, ISBN 0849355087 9780849355080 0849355097, FL, USA.