1. FYS 4250 Kap.10 Chemical biosensors
Chemical biosensor = sensor that produces an electric signal proportional to the concentration of a biochemical analyte
Each cell = a chemical factory
Important critical care analytes => blood levels of pH, pCO2, HCT, Hgb, O2 saturation, electrolytes Na, K, Ca and Cl
PNA

2. Dissosiation curves hemoglobin
Measurement of partial pressure of O2, CO2, and pH are critical -> may lead to fatal conditions if left uncorrected
98% of blood -> Hb, 2% dissolved in plasma
Saturation (amount of O2 bound to Hb) = ( [HbO2]/[Total Hb] ) x 100
Sigmoid shape
Total content of O2 in blood is directly related to SO2 for any [Hb] -> dissolved O2 is small

3. pH-measurement pH = -log(10)[H+] normal range <7.38, 7.44>
Decreased pH = respiratory acidosis (metabolic/respiratoric)
Generates an electrical potential when solutions of differing pH are placed on the two sides of the membrane. (Reacts only to specific ion)
Approach of Hydrogen outside -> positive charges inside ionic solution
60 mV pr pH unit (Nernst equation) -> pH range of only 0.06 units -> measure changes of 0.1 mV
Known pH inside (HCl)
Salt bridge to prevent chemical constituents of the specimen from affecting the voltage of the reference electrode
pH meter -> exremely high input impedance (internal impedance of the pH electrode is in the 10 to 100 Mohm range

4. pCO2 (Severinghaus) electrode
Relationship between log pCO2 and pH is linear over the range of 1.3 to 12 kPa = range of clinical interest
One specimen chamber and one pH electrode chamber
Only a proportional relationship -> calibrate the instrument before each use

5. pO2 (Clark) electrode
Oxidation at the reference electrode: 4Ag + 4Cl- -> 4AgCl + 4e-
Reduction at cathode: O2 + 2H2O+4e- ->2H2O2 + 4e- -> 4OH-
4OH- + 4KCl -> 4KOH + 4Cl-
The relating current is linearly proportional to the number of O2 molecules in solution
PO2 level is zero = background current -> part of the calibration procedure
Consumes O2

6. Polarografic oxygenmeasurement

7. Spectrophotometry blood
Optical absorption spectra for oxyhemoglobin
805 nm independent of degree of oxygenation = isobestic wavelength (infrared)

8. Oximeter
webstFig 10_7 crop ny.jpg

9. Fiberoptic oximetry
Warning: Hb has a strong affinity for CO, -> optical spectra overlap causing an error

10. Fiberoptic pH sensor Colorimetric indicator, pH sensitive dye.
Acidic or basic solution with different optical spectra

11. Optical absorbance pH sensitive dyes
Indicating that the optical absorbance peak increases with increasing pH
Ratio of green to red light transmitted through the dye is:
R = k x 10 exp [-C/((10exp -delta) + 1)]

12. Fluorescent dye sensor
Irreversible reactions -> long-lasting reagent
Cellulose matrix
Fluorescent dyes emit light energy at a wavelength different from that of the excitation wavelength, which they absorb

13. pH-sensitive dyes
Because of the separation between excitation and emission wavelengths, use a single optical fiber both for the delivery of light energy and for its reception from that sensor

14. Oxygen-sensitive dyes
Principle of fluorescence or luminescence quenching of oxygen -> energy lost. With O2 present-> transfer of energy to oxygen molecule->competes with energy decay modes ->increased luminescence by increasing loss of energy to oxygen
Irradiated by light at given wavelength -> when oxygen present -> fluorescence is quenched = dye fluoresces for a shorter period of time. (Inversely proportional to the partial pressure of Oxygen in the environment)
Poor SNR for high O2 levels

15. Fiberoptic oxygensensor

16. Multigas fiberoptic sensor
System considerations
Operating temp: 15 to 42 deg C
pH from 6.8 to 7.8
pCO2 from 10 to 100 mmHg
pO2 from 20 to 500 mmHg
Sterilizable and biocompatible
Must not be affected by naturally occurring substances as proteins

17. Ion-sensitive field-effect transistor
Ion concentration modulates the current between source and drain
Low cost microminiature sensor (IC)
Small sizes
Low measurement time
Main challenge: Satisfactory encapsulation of the ISFETs to protect electric characteristics. (Will deteriorate as a result of water vapor entering from the environment)

18. Potassim ion sensitive ISFET

19. Pulsoxymetry light absorption
Analyzing the AC component with two wavelengths. DC component is used to normalize AC signals
Absorbance or reflection
2.5% accuracy within %

20. Multiparameter monitor

21. Transcutaneous oxygen- transducer

22. Transcutaneous CO2 transducer
More accurate than tcPO2, PCO2 is less dependent on skin blood flow.
Heating increase PCO2 -> solubility decreases with an increase in temperature, cell metabolism is directly correlated to temperature, rate of CO2 diffusion through stratum corneum increases with temp

23. Enzym-electrode for glucose in blood
Instability of the immobilized enzyme and fouling of membrane surface

24. Fluorescense glukose-sensor i blod
Lack of long-term stability of the reagent, slow response time and dependence of the measured light intensity on the amount of reagent (small and may change over time).

25. Fiberoptic glucose-sensor in blood

26. Glukose IR transmisjonsspektrum