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© SENSORIN 2009
1
Elicia Wong, PhDElicia Wong, PhD
Revolutionary Revolutionary Technology in pH Technology in pH
MeasurementMeasurement
Mar 17-19, 2009Mar 17-19, 2009
© SENSORIN 2009
2
2 L 80 L400 L
2,000 L10,000 L
Upstream Process Downstream Process
pH ControlpH Control
Why is it a problem in bioprocessing?Why is it a problem in bioprocessing?
Wide Applications:Wide Applications:
Why is it Important in bioprocessing?Why is it Important in bioprocessing?
Pharmaceutical/biotechnology (medicine)
Cosmetic (perfume)
Food and beverage (wine, sugar)
Water purification & wastewater treatment
Petroleum/deep sea/outer space explorationCritical quality parameter for cell and bacterial growth and metabolic activity, productivity and consistency.
Drifting
Fouling
Calibration
© SENSORIN 2009
3
Potentiometric pH measurement
OutlineOutline
Existing pH measurement technologies
Optical pH measurement
Glass electrodeIon-selective field effect transistor (ISFET)
New technology
Amperometric pH measurement
© SENSORIN 2009
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External reference electrode
Measuring electrode
High impedance pH meter
Glass fritGlass membrane
Inner solution
Metal wire
Voltage difference builds up on the sides of the glass membrane due to difference between H+ activities on both sides
This voltage difference is measured with the help of an external reference electrode
Often reference and measuring electrodes are combined in one single structure
Fragile, wet storage, long term drift, requires frequent calibration
Potentiometric Approach – Glass Potentiometric Approach – Glass electrodeelectrode
Glass frit
Inner solution
External reference electrode
High impedance pH meter
Glass membrane
Glass electrode
© SENSORIN 2009
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Ion-Selective Field Effect Ion-Selective Field Effect TransistorTransistor
Vgs
Electron path
Vds
DrainSource
Ion-selective interface
Insulator Insulator
External reference electrodeAnalyte
solution
Cathode (-)
Anode (+)
--
- --
-
++
+ ++ + +
No current flows
- - -
Current flows
H+H+H+
Four major components: Source (s), Drain (d), Ion-selective interface and Gate (g).
Hydrogen ions at or near the ion-selective interface will cause a variable voltage potential (Vgs – Vds)
Solid state device
© SENSORIN 2009
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Photo-detector
Optical pH Measurement Optical pH Measurement SystemSystem
Photodetector, optical fiber, sensor
Sensor = fluorophore on solid support
An incident beam of light is passed to the sensor, where it interacts with the fluorophore. The emitted light intensity is pH dependent
Keep in dark (photo-bleaching)
Sensor
Optical light guide
Incident beam
Emitted light
© SENSORIN 2009
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Comparison Comparison
FeatureFeatureGlass Glass
ElectrodeElectrode ISFETISFET OpticalOptical
RobustnesRobustnesss
Glass (fragile)
Solid state Solid state
CalibrationCalibrationRequired (frequently)
Required (longer calibration interval)
Required (factory+on site)
StabilityStability Drift Drift Drift
MaintenanMaintenancece
Intensive (wet storage)
Easy (dry storage)
Intensive (kept in dark (photo-bleaching)
TemperatuTemperature Rangere Range
Wide Wide Narrow
pH rangepH range 0-14 0-14 5-9 (in ranges)
Biological Biological FoulingFouling
Occur Occur Occur
SensitivitySensitivity Low Medium Good
© SENSORIN 2009
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pH-sensitive interfacesemiconductor
Amperometric pH SensorAmperometric pH Sensor
Voltage (V)
Cu
rre
nt
(i)
Counter electrode
Internal reference
Power supply
iV
H+
H+H+
H+
VV ii
pH-sensitive interfacesemiconductor
H+ H+ H+ H+
VV ii
Voltage (V)
Cu
rre
nt
(i)
pH-sensitive interface + Internal reference
External reference electrode
Counter electrode
Reference electrodeAnalyt
e solution
pH-sensitive interface
© SENSORIN 2009
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pH (unit)
Vo
lta
ge
(V
)slope
tconsVoltagediffpH
tan)(
Self-CalibratingSelf-Calibrating
Voltage (V)
Cu
rren
t (i
)
pH 4
pH 7
pH 10
Internal reference = pH insensitive molecule
pH sensitive pH sensitive moleculesmolecules
Internal Internal referencereference
© SENSORIN 2009
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StabilityStability
Voltage (V)
Cu
rre
nt
(i)
Both the proprietary pH sensitive and insensitive molecules are chemicallychemically stable (won’t leach) and thermally stablethermally stable (able to withstand high temperature up to 250 C).
No degradation in performance with continuous operation and after heat sterilization.
Voltage (V)
Cu
rre
nt
(i)
Responses were Responses were observed after observed after multiple multiple autoclaving cycles autoclaving cycles (measurement (measurement performed after performed after each autoclaving each autoclaving cycle)cycle)
Continuous Continuous operationoperation
No degradation in No degradation in signal with 2-day signal with 2-day continuous continuous operation after operation after autoclavingautoclaving
Multiple Multiple AutoclavingAutoclaving
© SENSORIN 2009
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Free from Biological FoulingFree from Biological FoulingpH detection relies purely on chemical interaction between hydrogen ion and sensing interface rather than membrane diffusion effect (glass electrode)
Voltage (V)
Cu
rren
t (i)
Voltage (V)
Cu
rren
t (i)
Continuous measurement in medium containing Continuous measurement in medium containing living cellsliving cells
pH insensitive pH insensitive moleculesmolecules
pH sensitive pH sensitive moleculesmolecules
Without pH Without pH controlcontrol
Detect change in pH from pH 7.82* to 7.01*
*pH verified by off-line pH measurements
pH-sensitive interfacesemiconductor
H+ H+ H+ H+
pH-sensitive interfacesemiconductor
H+ H+ H+ H+
pH-sensitive interfacesemiconductor
H+ H+ H+ H+
pH-sensitive interfacesemiconductor
pH-sensitive interfacesemiconductor
H+ H+ H+ H+
- H+
H+
Clotting of glass membrane
© SENSORIN 2009
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Summary ChartSummary Chart
FeatureFeatureGlass Glass
ElectrodeElectrode ISFETISFET OpticalOpticalAmperometric Amperometric
SensorSensor
RobustnessRobustnessGlass (fragile)
Solid state Solid state Solid state
CalibrationCalibration
Required (frequently)
Required (longer calibration interval)
Required (factory)
Self calibrated
StabilityStability Drift Drift Drift No drift
MaintenanceMaintenance
Intensive (wet storage)
Easy (dry storage)
Intensive (Kept in dark (photo-bleaching)
Easy (dry storage)
Temperature Temperature RangeRange
Wide Wide Narrow Wide
pH rangepH range 0-14 0-14 5-9 (in ranges) 0-14
Biological Biological FoulingFouling
Occur Occur Occur NO
SensitivitySensitivity Low Medium Good Good
Ideal for Ideal for bioprocess pH bioprocess pH measurementmeasurement