SENSOR

Abstract

The invention provides a physiological sensing device for the measurement of pCO2, the device comprising: (i) a closed chamber bounded, at least partially, by a carbon dioxide permeable membrane; and (ii) at least two electrodes within said chamber, wherein said chamber contains a substantially electrolyte-free liquid in contact with the electrodes and the membrane and wherein the liquid comprises at least one metal or metalloid ion.

Claims

1. A physiological sensing device for the measurement of pCO.sub.2, the device comprising: (i) a closed chamber bounded, at least partially, by a carbon dioxide permeable membrane; and (ii) at least two electrodes within said chamber, wherein said chamber contains a substantially electrolyte-free liquid in contact with the electrodes and the membrane and wherein the liquid comprises at least one metal or metalloid ion.

2. A sensing device as claimed in claim 1, wherein the at least one metal or metalloid ion is selected from the group consisting of transition metals, Li, Na, Be, Mg, B, Al, Ga, In, Tl, Nh, Si, Ge, Sn, Pb and Fl.

3. A sensing device as claimed in claim 1, wherein the at least one metal or metalloid ion is selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, Ag, Cd, Al, Ga, In and Tl.

4. A sensing device as claimed in claim 1, wherein a mixture of metal and/or metalloid ions are present.

5. A sensing device as claimed in claim 1, wherein the concentration of the metal and/or metalloid ions is in the range 0.01 to 20 mmolL.sup.−1.

6. A sensing device as claimed in claim 1, wherein the at least one metal or metalloid ion is provided in the form of a hydroxide.

7. A sensing device as claimed in claim 1, wherein the liquid comprises water.

8. A method for measuring pCO.sub.2, said method comprising using a sensing device as defined in claim 1.

9. The use of a sensing device as claimed in claim 1 for measuring pCO.sub.2.

10. A method for measuring pCO.sub.2, said method comprising the step of measuring the change in conductivity of a liquid in the presence of CO.sub.2, wherein said liquid comprises at least one metal or metalloid ion.

11. A method for amplifying the change in conductivity of a liquid in the presence of CO.sub.2, said method comprising adding at least one metal or metalloid ion to said liquid.

12. The sensing device as claimed in claim 3, wherein the at least one metal or metalloid ion is selected from the group consisting of Al, Ni, Ag, Cu, Co and Pd.

13. The sensing device as claimed in claim 4, wherein a mixture of Cu and Al ions are present.

14. The sensing device as claimed in claim 7, wherein the liquid comprises substantially electrolyte-free water.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0070] FIG. 1: Schematic diagram of experimental set-up for Example 1

[0071] FIG. 2: CO.sub.2 detection prior to addition of metal ions

[0072] FIG. 3: CO.sub.2 detection after addition of CuOH

[0073] FIG. 4: CO2 detection after addition of AlOH and CuOH

[0074] FIG. 5: Relationship between sensitivity and metal ion

[0075] FIG. 6: Relationship between sensitivity and concentration

EXAMPLES

Example 1

[0076] The experimental set-up shown in FIG. 1 was constructed. A gas mixture of CO.sub.2 and N.sub.2 was bubbled through diffusers into de-ionised water. The composition of the mixture was controlled by two computer controlled mass flow controllers. Two 40 mL beakers were filled with de-ionised water at ambient temperature. Each beaker contained a gas diffuser and two sensors (one each of type S1 and S2). Beaker 2 also contained a reference sensor. Sensors S1 and S2 comprised of gold stripe electrodes located diametrically opposed on the outside of a cylindrical polymer carrier substrate. S2 electrode spacing approximately 0.7 mm, lengths 5 mm, S1 spacing approximately 1.7 mm, electrode lengths 10 mm. The reference sensor consisted of two 10 mm cylindrical steel electrodes 175 um diameter, suspended 1 mm apart. The sensors were connected to a PC through an analogous digital converter and conditioning electronics.

[0077] The gas mixture composition was varied with time following the sequence O % CO.sub.2, 6% CO.sub.2, 10% CO.sub.2, 14% CO.sub.2, 6% CO.sub.2 and 0% CO.sub.2 over a time period of 30 minutes and the response of the sensors followed. The Results are shown in FIG. 2.

[0078] Copper hydroxide (2.5 mmolL.sup.−1) was then added to Beaker 1 and the gas mixture composition was varied with time following the sequence O % CO.sub.2, 6% CO.sub.2, 14% CO.sub.2, 20% CO.sub.2 and 0% CO.sub.2 over a time period of 30 minutes and the response of the sensors followed. The Results are shown in FIG. 3. The signal can be seen to increase significantly for Sensors 1 and 2 in Beaker 1 with the metal ions present compared to Sensors 1 and 2 in Beaker 2 which contains only de-ionised water. Sensitivity to CO.sub.2 is shown to increase by a factor up to around 9 on addition of the metal hydroxide.

Example 2

[0079] The same experiment as described in Example 1 was repeated, except that a 1:1 ratio of AlOH (3.2 mmolL.sup.−1) and CuOH (2.5 mmolL.sup.−1) were added to Beaker 1 and the gas mixture composition was varied with time following the sequence 0% 6% CO.sub.2, 10% CO.sub.2, 14% CO.sub.2, 20% CO.sub.2, 6% CO.sub.2 and 0% CO.sub.2 over a time CO.sub.2, period of 30 minutes and the response of the sensors followed. The Results are shown in FIG. 4. Again, the signal can be seen to increase significantly for Sensors 1 and 2 in Beaker 1 with the metal ions present compared to Sensors 1 and 2 in Beaker 2 which contains only de-ionised water.

Example 3

[0080] The effects of changing the metal ion and concentration on the increase in sensitivity were investigated using the same set-up described for Example 1. The results are shown in FIGS. 5 and 6.

[0081] FIG. 5 shows that all of NiOH, AlOH and CuOH give an increase in sensitivity to CO.sub.2 measurement when added to de-ionised water, with CuOH showing the highest increase. The concentrations of NiOH, AlOH and CuOH were 2.7 mmolL.sup.−1, 3.21 mmolL.sup.−1 and 2.56 mmolL.sup.−1, respectively.

[0082] FIG. 6 shows that a significant increase in sensitivity is observed for a mixture of CuOH, AlOH and NiOH over a wide concentration range. Mix1 at 0.1% contains NiOH, AlOH and CuOH at concentrations of 10.24 mmolL.sup.−1, 12.84 mmolL.sup.−1 and 10.8 mmolL.sup.−1, respectively. The concentrations were decreased by a factor of two each time, thus Mix1 at 0.05% contains NiOH, AlOH and CuOH at half the concentration of Mix1 at 0.1% and so on.