Blood pH is tightly regulated in the human body and generally lies between 7.3-7.5. pH monitoring is important in medical diagnosis and treatment, including for major diseases, surgeries, and drug effects. Various methods exist for measuring pH, including glass electrodes, metal-metal oxide electrodes, pH sensitive FETs, conductimetric sensors, and fiber optic sensors. Each method has advantages and limitations for different applications such as invasiveness, accuracy, and ability for continuous monitoring. Temperature also affects pH measurement so calibration is required.

1. Blood pH MeasurementSuhasDeshpandeEE506 Dr. Druzgalski

2. OutlinepHBlood and pHpH MonitoringGlass ElectrodesMetal-metal oxide electrodespH sensitive FETsConductimetric pH sensorsFiber optic pH sensorsTemperature dependenceCalibration Model G pH meter (Beckman Coulter, Inc. 1936)http://www.ph-meter.info/pH-meter-history

3. pH DefinedChemically: measure of acidity or basicity of a fluidPhysically: Measure of concentration of H+ ionsMathematically: pH = -log10[H+] Technically: Power or Potential of hydrogen ions in the fluid.

4. Blood pHImportance in medical fieldDiagnosis of major acid base disorders, cancers renal failures, ischemia

5. Diagnosis of patients in ICU

6. Major surgeries like open heart surgery

7. Diagnosis of effect of a particular drug on the patientBlood pH is very tightly regulated in human body generally lies between 7.3-7.5Acute changes in blood pH induce powerful regulatory effects at the level of the cell, organ, and organismThe pH of blood plasma and various other body solutions is tightly regulated variables in human physiology

8. pH monitoring

9. pH measurementGlass ElectrodesMetal-metal oxide electrodespH sensitive FETsConductimetric pH sensorsFiber optic pH sensors

10. Glass ElectrodesEMF is developed between the measuring electrode and reference electrode Time consumingNeeds blood sample to be takenwww.ph-meter.info/pH-electrode-construction

11. Metal-metal oxide electrodesWorking on similar principleRhodium-iridium can be used as electrodeChemical equilibrium between salt-salt solution cause potential between the electrodes Easy to miniaturize and CMOS compatible

12. Comparing MMO Electrodes

13. pH sensitive FETsBased on MOSFET device can be manufactured using CMOS technologyVarious gate materials used SiO2, Si3N4, Al2O3

14. Compare different ISFETs

15. Conductimetric sensorsBased on the change in the conductivity upon contact with changing pHPolymers such as Polyaniline (PANI) show wide range of conductivities with varying pH for different dopings.

16. Conductimetric sensors

17. Fiberoptic pH sensorsSafe small can be placed in patient’s arteriesBased on absorption or fluorescenceIn-vitro analysis makes continuous monitoring possibleIndicator dye Phenol red can be used for the range 7.0-7.5http://www.oceanoptics.com/Products/phsensor.asp

18. Optical pH Sensor SystemTwo LEDs with different wavelenthsFlorescence measured using photo detectorAmount of florescence determines the pHResult of optical sensor linear, with max error of 0.18 and avg error 0.061

19. Comparing different electrodes

20. Temperature dependenceTemperature dependence of pH increases with increase in bascicityFor basic solutions pH depends on autoprotolysisof water which is temperature dependent