2 pH Control Wide Applications: Why is it Important in bioprocessing? Pharmaceutical/biotechnology (medicine)Cosmetic (perfume)Food and beverage (wine, sugar)Water purification & wastewater treatmentPetroleum/deep sea/outer space explorationWhy is it Important in bioprocessing?Critical quality parameter for cell and bacterial growth and metabolic activity, productivity and consistency.2 L80 L400 L2,000 L10,000 LUpstream ProcessDownstream ProcessWhy is it a problem in bioprocessing?DriftingFoulingCalibration
4 Potentiometric Approach – Glass electrode External reference electrodeMeasuring electrodeHigh impedance pH meterGlass fritGlass membraneInner solutionMetal wireGlass fritInner solutionExternal reference electrodeHigh impedance pH meterGlass membraneGlass electrodeVoltage difference builds up on the sides of the glass membrane due to difference between H+ activities on both sidesThis voltage difference is measured with the help of an external reference electrodeOften reference and measuring electrodes are combined in one single structureFragile, wet storage, long term drift, requires frequent calibration
5 Ion-Selective Field Effect Transistor VgsExternal reference electrodeAnalyte solutionSolid state deviceInsulatorIon-selective interfaceInsulatorSourceDrainElectron pathVdsCurrent flowsFour 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)Cathode (-)No current flowsAnode (+)H+-----+
6 Optical pH Measurement System Photo-detectorPhotodetector, optical fiber, sensorSensor = fluorophore on solid supportAn incident beam of light is passed to the sensor, where it interacts with the fluorophore. The emitted light intensity is pH dependentKeep in dark (photo-bleaching)SensorOptical light guideIncident beamEmitted light
10 StabilityBoth the proprietary pH sensitive and insensitive molecules are chemically stable (won’t leach) and thermally stable (able to withstand high temperature up to 250 C).No degradation in performance with continuous operation and after heat sterilization.No degradation in signal with 2-day continuous operation after autoclavingResponses were observed after multiple autoclaving cycles (measurement performed after each autoclaving cycle)Continuous operationMultiple Autoclaving
11 Free from Biological Fouling pH detection relies purely on chemical interaction between hydrogen ion and sensing interface rather than membrane diffusion effect (glass electrode)- H+Clotting of glass membraneH+Continuous measurement in medium containing living cellspH sensitive moleculesDetect change in pH from pH 7.82* to 7.01*Without pH controlpH insensitive molecules*pH verified by off-line pH measurements
12 Ideal for bioprocess pH measurement Summary ChartIdeal for bioprocess pH measurementFeatureGlass ElectrodeISFETOpticalAmperometric SensorRobustnessGlass (fragile)Solid stateCalibrationRequired (frequently)Required (longer calibration interval)Required (factory)Self calibratedStabilityDriftNo driftMaintenanceIntensive (wet storage)Easy (dry storage)Intensive (Kept in dark (photo-bleaching)Temperature RangeWideNarrowpH range0-145-9 (in ranges)Biological FoulingOccurNOSensitivity LowMediumGood Good
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